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Near-patient test for c-reactive protein in general practice: assessment of clinical, organizational, and economic outcomes.

C-reactive protein (CRP) [3] is an acute phase protein widely used for the diagnosis and follow-up of infectious diseases in hospitals (1-4). In general practice, CRP is found valuable in the diagnosis of bacterial diseases and in the differentiation between bacterial and viral infections (5-7). Often the diagnostic value of CRP is found superior to that of the erythrocyte sedimentation rate (ESR) (7-9) and superior or equal to that of the white blood cell count (WBC) (5, 8, 9).

In Denmark, general practitioners (GPs) request CRP by mailing blood samples to hospital laboratories, and the test is ordered for 34% of all patients having a blood sample mailed (10). Several near-patient tests for CRP measurements are available commercially. We have evaluated one of these tests (NycoCard[R] CRP) and found it reliable and robust for the use in general practice (11). In questionnaire surveys, it has been proposed that knowing the CRP value while having the patient in the office may give GPs better guidance for the prescription of antibiotics than ESR (12,13).

Implementation of near-patient tests in general practice should be based on an outcomes assessment with documentation for the clinical outcomes (14). However, outcomes for the organization and economic outcomes are important features and should be included in an assessment (15). Therefore, results of a technology assessment should be available before the decision to introduce the test is made (16, 17).

The aim of this study was to assess the clinical, organizational, and economic consequences of introducing a near-patient test for CRP measurements in general practice, with special focus on the clinical use of the test, the additional use of ESR, prescription of antibiotics, and utilization of the hospital laboratory service.

Materials and Methods

The catchment area of the hospital laboratory at the Vejle County Central Hospital (Vejle Hospital) covers 136 000 inhabitants and 41 general practice clinics (90 GPs), of which all were invited to participate in this study; 29 clinics (70.1%) accepted [a total of 64 GPs (71.1%)].

INTERVENTION

The clinics were randomized into two groups. One group was given access to a near-patient test for CRP (NycoCard CRP Whole Blood; Nycomed Pharma) in the office (intervention), whereas the other group had to order CRP as usual, mailing a blood sample to the laboratory (control). After a period of 3 months, the two groups interchanged their status (crossover). The first period of intervention and control was 3 months (April-June 1996), and the second period was 4 months (July-October 1996). All clinics received an introductory visit with a demonstration by the manufacturer before their intervention period. No clinical guidelines for the use of CRP were distributed to the clinics.

INCLUSION OF PATIENTS

The GPs filled out a registration card for each patient when a CRP was measured in the office or requested at the laboratory. The date for the consultation, the tentative diagnosis, and the CRP value were registered together with the patient's personal registration number.

THE DANISH HEALTH SERVICE SYSTEM AND THE LABORATORY INFORMATION SYSTEM

All inhabitants in Denmark have a personal registration number, and it is therefore possible to collect information about any person from independent registries (18). Of the population, 97% are registered at their GPs (19). The GPs receive a basic fee from the Danish Health Service System for every registered person and an extra fee for several specified services such as consultations, laboratory tests, and mailing of patient samples to laboratories. These services, as well as prescription of drugs, are registered by the Health Service System and can, on application, be used for scientific purpose (18). Partnership general practices have the same registration number, which allows no differentiation between individual GPs in a clinic. In the county of Vejle, all test results from hospital laboratories are stored in a Laboratory Information System for 5 years for all 340 000 inhabitants.

OUTCOME MEASUREMENTS AT THE CLINIC LEVEL

From the regional office of the Health Service System, we received data on the following: (a) the number of patients registered at each clinic; (b) the date of consultation and personal registration number for all patients receiving one of the following services: ESR, WBC, antigen test for group A streptococci, bacterial culture, urine susceptibility test, and microscopy of urine and bacteria; and (c) all antibiotics dispensed in 1996.

From the Laboratory Information System at Vejle Hospital, we received data for all blood tests requested in 1996.

OUTCOME MEASUREMENTS AT THE PATIENT LEVEL

Some outcome measurements were available only at the patient level, including the number of follow-up consultations.

STATISTICAL ANALYSES

Results were calculated at the patient level by use of X' tests, unpaired Mests, and Mann-Whitney tests. At the clinic level crossover Mest statistics were used (20). The inclusion rates were assessed for each clinic in intervention and control periods. If a clinic had an inclusion rate <75% in either period, all patients from that clinic were excluded from the study. The clinic itself was not excluded because all outcome measurements at the clinic level were based on data from the Health Service System and the Laboratory Information System, and therefore were independent of the registration of included patients.

ETHICS

The study was approved by the Danish Data Protection Agency, and the local scientific ethics committee was informed about the study.

Results

It was possible to evaluate data in this study, both at the level of included patients and at the overall level of participating general practice clinics. Results at the level of included patients were suitable to describe the categories of patients having their CRP measured and to evaluate prescription of antibiotics at patient level. Results at the level of included patients are presented in Tables 1-4. Results at the level of general practice clinics were suitable for organizational and economic evaluation, and these results are presented in Tables 5 and 6.

RESULTS AT THE LEVEL OF INCLUDED PATIENTS

During the study period, 2915 patients were registered at their GPs: 1560 (53.3%) during intervention periods and 1355 (46.5%) during control periods. During the intervention periods, all 29 clinics had an inclusion rate near 100%; however, during the control periods, 13 clinics had an inclusion rate <75% (range, 6-67%). All 1041 patients registered by these clinics were excluded. Of the remaining 1874 patients, 21 were excluded because of incomplete registration of personal registration numbers, leaving 919 patients included in the intervention periods and 934 patients included in the control periods.

Sex and age characteristics. The mean age of the included patients was 53.7 years [95% confidence interval (CI), 52.8-54.6%], and 60.2% (95% CI, 58.0-62.4%) of the patients were women.

Reasons for measuring CRP and disease characteristics. The disease characteristics for the included patients are given in Table 1. During intervention periods, the use of CRP was significantly higher for "diagnosis of new diseases" and "infectious diseases". For patients with sinusitis, the use of CRP during intervention periods was threefold higher than during the control periods, whereas changes for other specified infectious diseases are insignificant. There was a significant decrease in follow-up testing during intervention periods. The decrease in follow-up testing was seen mainly in the group of patients without infections, with a decrease from 18.1% during control periods to 12.8% during intervention periods (P = 0.002). Follow-up testing for patients with infectious diseases decreased from 8.1% to 5.9% (P = 0.07). The use of CRP for chronic inflammatory diseases and other diseases was equally distributed in the periods.

Additional tests, consultations, and laboratory services. The number of additional tests and consultations together with the use of laboratory services is given in Table 2. The use of ESR was significantly (11%) lower during intervention periods, and the decrease was significant both for patients with CRP values within the health-related reference interval and for patients with high values. For patients with CRP values [less than or equal to] 10 mg/L, the decrease was 9.1% (P = 0.002); for patients with CRP values between 10 and 25 mg/L, the decrease was 12% (P = 0.043); and for patients with CRP values [greater than or equal to] 25 mg/L, the decrease was 12.6% (P = 0.014). The use of other supplementary tests remained unchanged. The use of follow-up telephone consultations was also lower during intervention periods, whereas the number of daytime and out-of-hours consultations was unchanged. During control periods, 140 patients (15.0%) had a blood sample forwarded for a CRP measurement only, but the total number of blood samples forwarded to the laboratory declined significantly, from 100% to 60.2%, during intervention periods, which is a reduction of nearly 40%. This reflects a reduction in the number of patient samples forwarded containing a request for other analyses in addition to a CRP measurement. The mean number of requests for additional laboratory tests for each forwarded blood sample was 4.8 tests in intervention periods and 5.5 tests in control periods (i.e., CRP exclusive). In both periods, creatinine, alanine aminotransferase, alkaline phosphatase, WBC, and potassium were the most frequently requested additional tests.

Prescription of antibiotics. In Table 3, the prescription of antibiotics is compared for different CRP concentrations. Patients with infection as the tentative diagnosis and with unspecific diagnoses such as fever, cough, or dyspnea are included. Patients in a follow-up course and with appendicitis were excluded. Antibiotics were prescribed for approximately one-third of all patients with a sign of infection during both intervention and control periods. During both periods, the frequency of prescription increases with an increased magnitude of CRP values (test for trend; P <0.0001). During both periods, 20% of the patients with a health-related CRP value received an antibiotic prescription. These patients had the same distribution of infectious diagnoses as described in Table 1.

There were no differences between types of antibiotics prescribed during intervention and control periods. In both periods, narrow spectrum penicillin was the most frequently used antibiotic (45%), followed by macrolides (22%), broad spectrum penicillins (20%), quinolones (8%), and sulfa drugs (3%).

Patient delays for collecting antibiotics. By comparing the date that CRP was measured in each patient with the date that the prescribed antibiotic was dispensed by a pharmacy, a delay for collecting antibiotics can be estimated for each patient (Table 4). Patients with a CRP value >50 mg/L had a significantly lower delay in collecting their antibiotics during intervention periods than during control periods.

RESULTS AT THE LEVEL OF GENERAL PRACTICE CLINICS

Intervention effects. Quick access to CRP measurements led to a reduction of the overall use of ESR by GPs of 8%, whereas their use of other tests was unchanged. The number of CRP tests forwarded to the laboratory was reduced by 65%, and the overall number of blood samples forwarded by GPs was reduced by 6% (Table 5).

Economic evaluation. The cost-effectiveness for CRP as a near-patient test was calculated (Table 6) on the basis of intervention effects (Table 5). Implementation of CRP in general practice gave a rise in costs for the Health Service System, but also considerable savings for the laboratories, yielding a total savings of $111160 per year for a Danish county with 340 000 inhabitants.

Selection bias. The 29 clinics participating in the study were compared with the 12 clinics in the catchment area that declined participation. There were no significant differences for the number of requests for CRP from the laboratory, the use of ESR, the prescription of antibiotics, and the number and ages of the GPs affiliated with the clinics. The same parameters were compared for the 16 clinics with an inclusion rate >75% and the 13 clinics with a low inclusion rate, and no significant differences were found.

Discussion

We have, under controlled and randomized conditions, given GPs access to quick CRP measurements and have used independent administrative registries to monitor changes in their behavior. This method is in contrast with previous published studies where GPs were asked if a CRP value had influenced their prescription of antibiotics or would have given them better clinical information compared with ESR (12, 13).

STUDY VALIDITY

Some clinics had a low inclusion rate in the control period. This probably reflects difficulties in remembering to include patients in a routine situation. To ensure a high internal validity, we excluded all patients from clinics with a low inclusion rate. In the test for selection bias, participating clinics were found representative for all clinics in the catchment area.

ESR

Some results in this study were found significant at the level of general practices as well as at the level of included patients. At the level of included patients, the use of ESR decreases from 46.3% for control patients to 35.3% for intervention patients (Table 2). If we look at the total use of ESR by GPs and not only at ESR used for the patients included in this study, the decrease remains significant, at a total of 8% (Table 5). This decrease was achieved after only 3 to 4 months of intervention, and the decrease will probably continue over a period of 4 to 5 years, as has been seen for clinical hospital departments introduced to CRP (21).

BLOOD SAMPLES MAILED TO THE LABORATORY

The number of blood samples forwarded from general practices to the laboratory decreased significantly both at the level of included patients and at the level of GPs. In a previous study, we found that CRP is requested in 34% of all blood samples mailed from general practices (10). In that study, it was not possible to detect whether CRP was requested as an additional test to other primarily ordered tests or whether CRP was actually the blood test necessitating the blood sample. The marked decrease in the number of forwarded blood samples found in this study indicates that CRP actually is a blood test that provokes a blood sample in general practice.

PRESCRIPTION OF ANTIBIOTICS

Surprisingly, we found no major changes in the prescription of antibiotics by GPs (Table 3). From previous published studies, it could be hypothesized that the overall use of antibiotics would remain unaffected on the basis of more appropriate use of antibiotics, which means a decrease in prescriptions of antibiotics to patients with low CRP values and an increase in the number of prescriptions to patients with high CRP values. In this study, we found that exactly the same number of patients were prescribed an antibiotic at a certain magnitude of CRP values, regardless of whether the test results were given within minutes or days (Table 3). This observation together with a same-day dispense rate of 70% for both periods (Table 4) illustrates that the effect of the clinical use of the test seems to be uniform for both intervention and control periods. In control periods, antibiotics were prescribed and dispensed before the GP knew the CRP value. The test result, therefore, was not included in the diagnostic process, but perhaps was used as a kind of quality assurance for the clinical decision. It appeared that this pattern of application was copied during the intervention periods, although the test result should have been used as a part of the clinical decision-making process.

The group of patients with CRP values within the health-related reference interval but having an antibiotic prescribed had exactly the same distribution of infectious diseases as seen for the whole study population (Table 1). This means that tentative diagnoses such as pneumonia, sore throat, and sinusitis were dominant and accounted for >60% of suspected infectious diseases (Table 1). In general practice, the diagnostic value of CRP of these three diseases is well documented (5, 6, 8). For suspected bacterial pneumonia, the negative predictive value of a CRP value <50 mg/L is 95%, which means that only 1 of 20 patients will have bacterial pneumonia and a CRP value <50 mg/L simultaneously (5). The predictive value of a CRP value <10 mg/L would be even higher; however, 20% of patients with health-related CRP values had an antibiotic prescribed. The focus of this study was to investigate changes in the behavior of GPs who have CRP as a near-patient test, not to assess the ability of CRP to distinguish between bacterial and viral infection; therefore, we did not analyze culture data on every patient suspected for an infectious disease. The available literature supports the ability of CRP, although it is an nonspecific marker of infectious disease, to distinguish between bacterial and viral diseases (5-13). If we accept this ability to distinguish between diseases, we should have seen a decrease in the prescription of antibiotics to patients with low CRP values during the intervention periods and an increase in the prescription of antibiotics to patients with high CRP values, but this was not seen. Therefore, it seems reasonable to assume that implementation of clinical guidelines for the use of CRP in general practice could give a more appropriate use of antibiotics.

For a single subgroup of patients, a quick CRP result had an effect. Patients tentatively diagnosed clinically as having an infectious disease and with CRP values >50 mg/L collected their antibiotics sooner from pharmacies when the CRP measurement was made in the clinics (Table 4). This suggests that the GPs encouraged their patients to collect their antibiotics the same day, because a high CRP value indicates not only a bacterial infection, but also the severity of the infection (4).

TELEPHONE CONSULTATIONS

At the level of included patients, a significant decrease in the number of telephone consultations during the follow-up periods during intervention was seen, probably reflecting that patients had received the test result at the primary consultation and that their case was then closed. It was not possible for us to evaluate this result at the level of GPs because we only had permission to receive data for follow-up consultations for included patients.

REASONS FOR MEASURING CRP

Regarding the reasons for CRP measurements, only small differences between the study periods were noticeable. For both periods, a major part of the tests was used for diagnosing a new disease; however, during intervention periods this use was significantly more frequent. This result reflects that the GPs found having the test result of the CRP test while the patient was still in the clinic more useful for diagnostic purposes. A decrease in the frequency of using CRP for follow-up purposes was revealed. CRP is known to be very useful for monitoring the treatment course of infectious patients, by using the patients as their own references (4). One could consider that a decrease in follow-up testing could give rise to several recurrences and, therefore, higher costs. We found that the decrease in follow-up testing was seen mainly for the group of patients with noninfectious disease, which typically means patients with chronic inflammatory diseases.

COST EFFECTIVENESS

Implementation of a near-patient test for CRP in general practice in the county of Vejle would give the Health Service System a direct cost of $69 400 per year. The laboratories in the county would save $180 560 per year; because the counties are the owners of the hospitals in Denmark, the overall cost reduction would be $111160 for the county of Vejle.

In conclusion, we have evaluated the clinical, organizational, and economic consequences of implementing a near-patient test for CRP in general practice. Although the clinical alterations were small but relevant, we still calculate a direct cost reduction of approximately $110 000 per year for a Danish county with 340 000 inhabitants. If implementation is followed by education and clinical guidelines, additional beneficial outcome effects seems possible, based on an additional reduction in the use of ESR and a more appropriate use of antibiotics.

This study received financial support from the Danish Medical Research Council (grant no. 9602265), The Danish Health Insurance Fund (grant no. 11/024-96), The Danish Research Foundation for General Practice (grant no. FF-2-02-16), The Fund for Medical Research in Vejle County (grant no. 13/1995), The Quality Assurance Fund for general practice in Vejle County, and The Memorial Foundation for Johs. M. Klein and wife U 664.14). Nycomed Pharma AS sponsored all near-patient tests, and their Danish division introduced GPs and their assistants to the test. We thank all participating GPs and their assistants. Jannie Kilsmark, Bodil Munk Hansen, and Frank Ingemann Jensen at the regional Health Service System office made it possible for us to use data from the health registries. At the Department of Clinical Chemistry, Vejle Hospital, EDP technologist Birgit J. Madsen extracted data from the Laboratory Information System and chief technologist Carsten Thomsen performed the economic assessment of laboratory services. Michael Vxth, Department of Biostatistics, Aarhus University, Aarhus, Denmark, gave statistical advice while we were designing the study and while we were writing the final manuscript.

References

(1.) Pourcyrous M, Bada HS, Korones SB, Baselski V, Wong SP. Significance of serial C-reactive protein responses in neonatal infection and other disorders. Pediatrics 1993;92:431-5.

(2.) Hansson LO, Axelsson G, Linne T, Aurelius E, Lindquist L. Serum C-reactive protein in the differential diagnosis of acute meningitis. Scand J Infect Dis 1993;25:625-30.

(3.) Oosterhuis WP, Zwinderman AH, Teeuwen M, van Andel G, Oldenziel H, Kerkhoff JF, et al. C reactive protein in the diagnosis of acute appendicitis. Eur J Surg 1993;159:115-9.

(4.) Hansson LO, Lindquist L. C-reactive protein: its role in the diagnosis and follow-up of infectious diseases. Curr Opin Infect Dis 1997;10:196-201.

(5.) Melbye H, Straume B, Aasebo U, Brox J. The diagnosis of adult pneumonia in general practice. The diagnostic value of history, physical examination and some blood tests. Scand J Prim Health Care 1988;6:111-7.

(6.) Hansen JG, Schmidt H, Rosborg J, Lund E. Predicting acute maxillary sinusitis in a general practice population. Br Med J 1995;311:233-6.

(7.) Hansson LO, Carlsson I, Hansson E, Hovelius B, Svensson P, Tryding N. Measurement of C-reactive protein and the erythrocyte sedimentation rate in general practice. Scand J Prim Health Care 1995;13:39-45.

(8.) Hjortdahl P, Melbye H. Does near-to-patient testing contribute to the diagnosis of streptococcal pharyngitis in adults? Scand J Prim Health Care 1994;12:70-6.

(9.) Lindback S, Hellgren U, Julander I, Hansson LO. The value of C-reactive protein as a marker of bacterial infection in patients with septicaemia/endocarditis and influenza. Scand J Infect Dis 1989;21:543-9.

(10.) Dahler-Eriksen BS, Lassen JF, Lund ED, Lauritzen T, Brandslund I. C-reactive protein in general practice-how commonly is it used and why. Scand J Prim Health Care 1997;15:35-8.

(11.) Dahler-Eriksen BS, Lassen JF, Petersen PH, Lund ED, Lauritzen T, Brandslund I. Evaluation of a near-patient test for C-reactive protein used in daily routine in primary healthcare by use of difference plots. Clin Chem 1997;43:2064-75.

(12.) Hjortdahl P, Landaas S, Urdal P, Steinbakk M, Fuglerud P, Nygaard B. C-reactive protein: a new rapid assay for managing infectious disease in primary health care. Scand J Prim Health Care 1991; 9:3-10.

(13.) Lindbxk M, Hjortdahl P. C-reaktivt protein i allmenpraksis. Et viktig diagnostisk hjelpemiddel ved infeksjoner. [C-reactive protein in primary care-a useful diagnostic tool in infections. In Norwegian; English summary]. Tidsskr Nor Lxgeforen 1998;118:1176-9.

(14.) Sandberg S. Near patient testing must improve patient care [Editorial]. Scand J Prim Health Care 1994;12:65-7.

(15.) Rainey PM. Outcomes assessment for point-for-care testing [Editorial]. Clin Chem 1998;44:1595-6.

(16.) Hobbs R. Near patient testing in primary care [Editorial]. Br Med J 1996;312:263-4.

(17.) Olesen F, Mainz J, Lassen JF. Research, technology assessment, and quality assurance. Eur J Gen Pract 1997;2:162-5.

(18.) Sorensen HT, Schulze S. Danish health registries [Editorial]. Dan Med Bull 1996;43:463.

(19.) Sorensen HT, Steffensen FH, Schonheyder HC, Gron P, Sabroe S. Use of microbiological diagnostics and antibiotics in Danish general practice. Int J Technol Assess Health Care 1996;12:745-51.

(20.) Armitage P, Berry G. Statistical method in medical research, 3rd ed. Oxford: Blackwell Science Ltd, 1995:620 pp.

(21.) Dahler-Eriksen BS, Lassen JF, Lauritzen T, Lund ED, Brandslund I. Forskelle i brugen of C-reaktivt protein og sxnkningsreaktion i almen praksis og p6 sygehus. Udvikling fra 1986 til 1995. [Differences in the quantitative use of C-reactive protein and erythrocyte sedimentation rate between general practice and hospital. A register-based study from 1986 to 1995. In Danish; English summary]. Ugeskr Lxger 1998;160: 4868-72.

(22.) Bland M. An introduction to medical statistics. Oxford: Oxford University Press, 1995:396 pp.

BJARNE STEEN DAHLER-ERIKSEN, [1,2] * TORSTEN LAURITZEN, [2] JENS FLENSTED LASSEN, [2] ERIK D. LUND, [1] and IVAN BRANDSLUND [1]

[1] Department of Clinical Chemistry, Vejle County Central Hospital, DK7100 Vejle, Denmark.

[2] Department of General Practice, University of Aarhus, DK-8000 Aarhus, Denmark.

[3] Nonstandard abbreviations: CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; WBC, white blood cell count; GP, general practitioner; and CI, confidence interval.

* Address correspondence to this author at: Department of Clinical Chemistry, Vejle County Central Hospital, DK-7100 Vejle, Denmark. Fax 45 75 82 18 14.

Received October 6, 1998; accepted February 3, 1999.
Table 1. Reasons registered by GPs for ordering a
CRP measurement and patients' tentative diagnoses.

 Intervention
 periods

 n %

Number of included patients 919 100.0
Purpose for CRP measurements
 Diagnosis of a new disease 528 57.5
 Screening 192 20.9
 Follow-up 172 18.7
 Not specified 27 2.9
Tentative diagnosis
 Infectious diseases
 with a frequency >2%
 Lower respiratory infections 194 21.1
 Upper respiratory infections 70 7.6
 Sinusitis 33 3.6
 Viral infections 29 3.2
 Pelvic inflammatory disease 27 2.9
 Infectious diseases 75 8.2
 with a frequency <2%
 Cystitis, gastroenteritis,
 cholecystitis,
 erysipelas, appendicitis,
 acute otitis media, wound
 infections, abscesses,
 diverticulitis,
 epididymitis, and mastitis
 Infections without 55 6.0
 additional specification
 Sum of infectious diseases 483 52.6
 Chronic inflammatory diseases 185 20.1
 Other diagnosis with 34 3.7
 frequency <2%
 Allergy, erythema,
 thyroiditis, asthma,
 gastritis, pancreatitis,
 irritable colon,
 malignant diseases,
 and anemia
 Unspecific diagnosis 94 10.2
 Gastrointestinal disease,
 fatigue, loss of weight,
 fever without apparent
 focus, cough, dyspnea,
 and dizziness
 Tentative diagnosis 123 13.4
 not specified

 Control
 periods

 n %

Number of included patients 934 100.0
Purpose for CRP measurements
 Diagnosis of a new disease 446 47.8
 Screening 217 23.2
 Follow-up 245 26.2
 Not specified 26 2.8
Tentative diagnosis
 Infectious diseases
 with a frequency >2%
 Lower respiratory infections 179 19.2
 Upper respiratory infections 53 5.7
 Sinusitis 12 1.3
 Viral infections 27 2.9
 Pelvic inflammatory disease 16 1.7
 Infectious diseases 81 8.7
 with a frequency <2%
 Cystitis, gastroenteritis,
 cholecystitis,
 erysipelas, appendicitis,
 acute otitis media, wound
 infections, abscesses,
 diverticulitis,
 epididymitis, and mastitis
 Infections without 43 4.6
 additional specification
 Sum of infectious diseases 421 45.1
 Chronic inflammatory diseases 189 20.2
 Other diagnosis with 39 4.2
 frequency <2%
 Allergy, erythema,
 thyroiditis, asthma,
 gastritis, pancreatitis,
 irritable colon,
 malignant diseases,
 and anemia
 Unspecific diagnosis 112 12.0
 Gastrointestinal disease,
 fatigue, loss of weight,
 fever without apparent
 focus, cough, dyspnea,
 and dizziness
 Tentative diagnosis 183 19.6
 not specified

 P (a) for
 difference between
 periods

Number of included patients
Purpose for CRP measurements
 Diagnosis of a new disease 0.0002
 Screening 0.51
 Follow-up 0.0007
 Not specified
Tentative diagnosis
 Infectious diseases
 with a frequency >2%
 Lower respiratory infections 0.34
 Upper respiratory infections 0.11
 Sinusitis 0.002
 Viral infections 0.84
 Pelvic inflammatory disease 0.11
 Infectious diseases 0.75
 with a frequency <2%
 Cystitis, gastroenteritis,
 cholecystitis,
 erysipelas, appendicitis,
 acute otitis media, wound
 infections, abscesses,
 diverticulitis,
 epididymitis, and mastitis
 Infections without 0.22
 additional specification
 Sum of infectious diseases 0.002
 Chronic inflammatory diseases 1.0000
 Other diagnosis with 0.68
 frequency <2%
 Allergy, erythema,
 thyroiditis, asthma,
 gastritis, pancreatitis,
 irritable colon,
 malignant diseases,
 and anemia
 Unspecific diagnosis 0.26
 Gastrointestinal disease,
 fatigue, loss of weight,
 fever without apparent
 focus, cough, dyspnea,
 and dizziness
 Tentative diagnosis 0.0004
 not specified

(a) [chi-square] test.

Table 2. Additional tests carried out in general
practice and numbers of consultants and services
from the hospital laboratory at the level of
included patients.

 Intervention
 periods

 n %

Number of included patients 919 100.0
Additional tests for infection
 No additional tests 514 55.9
 ESR 324 35.3
 Antigen test (group A streptococci) 58 6.3
 WBC 45 4.9
 Bacteriological culture 31 3.4
 Bacteriological microscopy (b) 4 0.4
 Urine microscopy 21 2.3
 Urine susceptibility test 31 3.4
Consultations within 7 days
 Daytime consultations 236 25.7
 Telephone consultations 491 53.4
 Out-of-hours consultations 39 4.2
Hospital laboratory
 CRP forwarded 93 10.1
 Blood samples forwarded 553 60.2

 Control
 periods

 n %

Number of included patients 934.0 100.0
Additional tests for infection
 No additional tests 429.0 45.9
 ESR 432.0 46.3
 Antigen test (group A streptococci) 40.0 4.3
 WBC 48.0 5.1
 Bacteriological culture 34.0 3.6
 Bacteriological microscopy (b) 2.0 0.2
 Urine microscopy 27.0 2.9
 Urine susceptibility test 34.0 3.6
Consultations within 7 days
 Daytime consultations 217.0 23.6
 Telephone consultations 582.0 63.3
 Out-of-hours consultations 36.0 3.9
Hospital laboratory
 CRP forwarded 934.0 100.0
 Blood samples forwarded 934.0 100.0

 P (a) difference
 between periods

Number of included patients
Additional tests for infection
 No additional tests 0.0001
 ESR <0.0001
 Antigen test (group A streptococci) 0.18
 WBC 0.99
 Bacteriological culture 0.98
 Bacteriological microscopy (b) 0.45
 Urine microscopy 0.80
 Urine susceptibility test 0.98
Consultations within 7 days
 Daytime consultations 0.24
 Telephone consultations 0.0001
 Out-of-hours consultations 0.76
Hospital laboratory
 CRP forwarded <0.0001
 Blood samples forwarded <0.0001

(a) [chi-square] test.

(b) Fisher exact test.

Table 3. Prescription of antibiotics
at different CRP values during
intervention and control periods. (a)

 Antibiotics
 prescribed

Intervention or
control period n %

Total number of patients
 I (b) 168 31.8
 C 154 32.6

No. with CRP [less than
or equal to]10 mg/L
 I 64 19.5
 C 57 20.1

No. with CRP 11-24 mg/L
 I 22 40.0
 C 23 32.4

No. with CRP 25-49 mg/L
 I 38 63.3
 C 20 55.6

No. with CRP [greater
than or equal to] 50 mg/L
 I 44 52.4
 C 54 66.7

 Antibiotics not
 prescribed

Intervention or
control period n %

Total number of patients
 I (b) 361 68.2
 C 318 67.4

No. with CRP [less than
or equal to]10 mg/L
 I 265 80.5
 C 227 79.9

No. with CRP 11-24 mg/L
 I 33 60.0
 C 48 67.6

No. with CRP 25-49 mg/L
 I 22 36.7
 C 16 44.4

No. with CRP [greater
than or equal to] 50 mg/L
 I 40 47.6
 C 27 33.3

 Total

Intervention or
control period n %

Total number of patients
 I (b) 529 100.0
 C 472 100.0

No. with CRP [less than
or equal to]10 mg/L
 I 329 100.0
 C 284 100.0

No. with CRP 11-24 mg/L
 I 55 100.0
 C 71 100.0

No. with CRP 25-49 mg/L
 I 60 100.0
 C 36 100.0

No. with CRP [greater
than or equal to] 50 mg/L
 I 84 100.0
 C 81 100.0

 P (c) for difference between
 periods I and C

Intervention or
control period

Total number of patients
 I (b)
 C 0.82

No. with CRP [less than
or equal to]10 mg/L
 I
 C 0.93

No. with CRP 11-24 mg/L
 I
 C 0.49

No. with CRP 25-49 mg/L
 I
 C 0.59

No. with CRP [greater
than or equal to] 50 mg/L
 I
 C 0.087

(a) See details for included patients in the text.
In both periods, the frequency of prescription
increases with increased magnitude of CRP values
(test for trend;

P <0.0001)(22).

(b) I, intervention; C, control.

(c) [chi-square] test.

Table 4. Patients' delay for collecting
their antibiotics at a pharmacy after
having CRP measured.

 Intervention Control
 periods period

 P (a) for
 difference
 between
 n % n % periods

All patients 168 100.0 154 100.0
 Delay in dispensing
 of antibiotics
 No delay 120 71.4 107 69.5
 1-2 days 24 14.3 27 17.5 0.80
 3-7 days 24 14.3 20 13.0

Patients with CRP 44 100.0 54 100.0
[greater than or
equal to]50 mg/L
 Delay in dispensing
 of antibiotics
 No delay 36 81.8 33 61.1
 1-2 days 7 15.9 12 22.2 0.0161
 3-7 days 1 2.3 9 16.7

(a) Mann-Whitney test.

Table 5. Changes in use of additional tests,
use of hospital laboratory services, and
prescription of antibiotics by GPs. (a)

 No. of tests per month
 per 1000 inhabitants

 Effects of
 Control intervention,
 period, mean mean change
 (95% CI) (95% CI)

Additional tests
 CRP, near-patient test 0.0 4.8 (3.3 to 6.2)
 ESR 10.3 (5.9-14.6) -0.8 (-1.4 to -0.1)
 Antigen test 8.4 (6.8-10.1) 0.0 (-1.2 to 1.2)
 (group A streptococci)
 WBC 0.9 (0.3-1.6) 0.0 (-0.1 to 0.1)
 Bacteriological culture 5.3 (3.8-6.8) -0.1 (-0.5 to 0.3)
 Bacteriological 0.9 (0.3-1.6) 0.0 (-0.4 to -0.4)
 microscopy
 Urine microscopy 2.8 (1.3-4.4) -0.1 (-0.3 to 0.1)
 Urine susceptibility 2.9 (1.8-4.0) 0.0 (-0.3 to 0.3)
Hospital laboratory
 CRP, forwarded 6.2 (4.3-8.1) -4.0 (-5.8 to -2.2)
 Blood samples forwarded 33.7 (27.9-39.5) -1.9 (-3.4 to -0.4)
Antibiotics
 Antibiotics 217.9 (191.8-244.0) -1.6 (-16.5 to 13.3)
 prescribed (DDD)
Total use of CRP
 measurements
 Near-patient 6.2 (4.3-8.1) 0.8 (-0.8 to 2.4)
 test + forwarded

 Change in P (b) for
 percentage effect of
 (95% CI) intervention

Additional tests
 CRP, near-patient test -8 (-14 to -1) 0.0221
 ESR 0 (-14 to 14) 0.97
 Antigen test
 (group A streptococci) 0 (-11 to 11) 0.58
 WBC -1 (-9 to 6) 0.72
 Bacteriological culture 0 (-44 to 44) 0.97
 Bacteriological
 microscopy -2 (-11 to 4) 0.51
 Urine microscopy 0 (-10 to 10) 0.94
 Urine susceptibility
Hospital laboratory -65 (-94 to -35) 0.0001
 CRP, forwarded -6 (-10 to -1) 0.0154
 Blood samples forwarded
Antibiotics -1 (-8 to 6) 0.83
 Antibiotics
 prescribed (DDD)
Total use of CRP
 measurements 13 (-13 to 39) 0.31
 Near-patient
 test + forwarded

(a) The 29 participating clinics service a catchment
area of 97 341 inhabitants, corresponding to 28.6%
for all inhabitants in the county of Vejle.
Results are normalized as number of tests per month
per 1000 inhabitants.

(b) t-test for cross-over designs (20).

Table 6. Cost-effectiveness of implementing
CRP as a near-patient test in general practice
in the county of Vejle, Denmark, (a) based on
effects of intervention reported in Table 5.

 Effects of
 intervention,
 Cost per units/month/1000
 quantity inhabitants
 (b) $ (95% CI)

Cost for the Health Service System
 ESR (d) 3.10 -0.8 (-1.4 to -0.1)
 Blood samples forwarded (e) 5.40 -1.9 (-3.4 to -0.4)
 CRP, near-patient tess (f) 6.20 4.8 (3.3 to 6.2)
Sum of costs for the
Health Service System
Cost for the hospital laboratories
 Handling of forwarded 7.70 -1.9 (-3.4 to -0.4)
 blood samples (g)
 Analysis of five additional 7.50 -1.9 (-3.4 to -0.4)
 blood tests (h)
 CRP, laboratory (i) 3.85 -4.0 (-5.8 to -2.2)
Sum of costs for the
hospital laboratories
Total sum of costs for
the county of Vejle
Total savings for the county
of Vejle would be $111 160
per year (95% CI, $25 700.00
to $196 550.00)

 Sum, (c) $/month/1000
 inhabitants (95% CI)

Cost for the Health Service System
 ESR (d) -2.48 (-4.3 to -0.3)
 Blood samples forwarded (e) -10.26 (-18.4 to -2.2)
 CRP, near-patient tess (f) 29.76 (20.5-38.4)
Sum of costs for the 17.02 (5.0-29.0)
Health Service System
Cost for the hospital laboratories
 Handling of forwarded -14.63 (-26.2 to -3.1)
 blood samples (g)
 Analysis of five additional -14.25 (-25.5 to -3.0)
 blood tests (h)
 CRP, laboratory (i) -15.40 (-22.3 to -8.5)
Sum of costs for the -27.26 (-48.2 to -6.3)
hospital laboratories
Total sum of costs for
the county of Vejle
Total savings for the county
of Vejle would be $111 160
per year (95% CI, $25 700.00
to $196 550.00)

(a) On January 1, 1996, the county of
Vejle had 339 818 inhabitants.

(b) Currency rate: $1.00 US is 6.50 Dkr.

(c) Results normalized as cost
per month per 1000 inhabitants.

(d) Fee to GP for measuring an ESR.

(e) Fee to GP for mailing a blood
sample to the hospital laboratory.

(f) Utensils and reagents cost $3.10
for each test, and the GP's fee is
supposed to be $3.10 as for an ESR.

(g) Receiving a mailed blood sample costs
$7.70, which includes unpacking,
registration of patients' data in the
Laboratory Information System, securing
of patients' personal registration number,
storage, and reporting of test result to
the requesting clinicians.

(h) Costs for specified blood tests are
variable depending on requirements for manpower,
utensils, and reagents. The five blood tests
ordered most frequently as additional tests with
a requested CRP are all inexpensive and cost from
$1.50 to $3.00. A cost of $1.50 is used.

(i) Cost for measuring a CRP at laboratory is $3.85.
COPYRIGHT 1999 American Association for Clinical Chemistry, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
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Article Details
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Title Annotation:Test Utilization and Outcomes
Author:Dahler-Eriksen, Bjarne Steen; Lauritzen, Torsten; Lassen, Jens Flensted; Lund, Erik D.; Brandslund,
Publication:Clinical Chemistry
Article Type:Clinical report
Date:Apr 1, 1999
Words:6320
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