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Clinical evaluation of the Cell-Dyn[R] 1700CS blood counter.

New generations of hematology analyzers produce fast and reliable data on blood count, while at the same time offering screening information on differential blood count. The aim of this study was to evaluate a Cell-Dyn [R] (CD) 1700CS (Abbott Diagnostics, Abbott Park, IL) hematology analyzer that determines 18 parameters, including three-part differential blood count.

A single unit instrument consists of a sample analyzer, data module section, and printer as a separate component. The analyzer contains the hardware to aspirate, dilute, and analyze each whole-blood sample from open and closed collection tubes or prediluted samples. Aspiration volume in open mode is 30 [micro]L, in closed mode 450 [micro]L, and in predilute mode 40 [micro]L. The data module section includes a computer controlling all operations and storing a total of 5000 numeric and graphic data results, color video display monitor, and keyboard. The keyboard allows entry of sample identification number, patient name, sex, date of birth, physician, collection date and time, and comments. In addition, limits and reference ranges can be printed with each patient's results.

Counting of blood cells is based on the volumetric impedance method, directly measuring white blood cells (WBC), red blood cells (RBC), hemoglobin (HGB), platelets, mean corpuscular volume (MCV), and mean platelet volume, and automatically calculating hematocrit (HCT), mean corpuscular hemoglobin (MCH), MCH concentration (MCHC), RBC distribution width, plateletcrit, and platelet distribution width. The instrument differentiates the subpopulations of lymphocytes, granulocytes, and the mid-cell fraction (eosinophils, basophils, monocytes, and precursors of WBCs) by electronic sizing. Specially formulated reagents cause the WBC membrane to shrink around the nucleus while keeping the cell intact, allowing separation of white cells according to their volume. Lymphocytes fall within the small-cell region, neutrophils within the large-cell region, and the remaining cells into the mid-size cell region. The three-part differential screen is provided with a region-flagging criteria (R-flags) system based on computer check of the three different cell populations' peaks and valleys histogram. Suspect flags are generated after the instrument has evaluated the three-part differential indicating the possible distribution or morphological abnormalities. CD 17000S utilizes five different alerts: R0, R1, R2, R3, and R4, plus a multiple alert designated RM (Fig. 1). "R" is an abbreviation for the region of the histogram, and the associated number indicates the portion of the histogram that is abnormal. "M" is displayed when multiple regions are abnormal. White cells falling beyond the anticipated normal range will trigger one of the alerts.

The instrument is calibrated for directly measured parameters with the Cell-Dyn calibrator according to the manufacturer's guidelines and does not require frequent recalibration when it is operated and maintained according to the manual recommendations. The system offers several quality-control (QO) options to monitor and validate instrument performance. Also, QC programs are designed to provide continual monitoring and confirmation of the instrument calibration.

Results of analytical evaluation showed that within-run precision (n = 30) for all parameters either measured or calculated was satisfactory and ranged from 0.63% (MCV) to 4.7% (mid-cell fraction) in open mode, and from 0.59% (MCV) to 4.93% (mid-cell fraction) in closed mode. Between-run CVs tested on three levels, low (n = 3 X 20), normal (n = 3 X 20), and high (n = 3 X 20) generally were <3%; higher values were observed only for platelet count determination in the abnormal low range for closed tube sampling (CV of 5.10% with an average platelet count of 63 X [10.sup.9]/L) and for mid-cell percentage for closed tube sampling (CV of 4.40-6.98%). The CVs for closed tube sampling were observed to be slightly higher than those for open tube sampling. Satisfactory CVs of between-day precision tested (n = 3 X 20) on three-level control material were obtained for most parameters, except for leukocyte count in the abnormal low range (CVs of 3.92% and 4.01% with an average leukocyte count of 2.1 X [10.sup.9]/L), platelet count in the abnormal low range (CV of 5.73%), and mid-cell percentages in both open and closed tube sampling (CV of 6.00-6.20%).

[FIGURE 1 OMITTED]

Results of blood count comparison obtained by simultaneous analysis of 156 patient samples on CD 17000S and MEK-8118K (Nihon Kohden, Tokyo, Japan) hematologic analyzers showed a satisfactory correlation for all the parameters tested, ranging from 0.967 for platelets to 0.994 for WBC, except for MCHC (r = 0.389 in closed and r = 0.344 in open mode). A low correlation coefficient for MCHC was also found by other authors [1-3], indicating a serious problem in MCHC measurement assuming that the differences probably reflected variations in cell sizing techniques used in various instruments, which would be of minor clinical significance. The comparison of open and closed mode of tube sampling was excellent for all the parameters tested, except for MCHC, showing a slightly higher CV (r = 0.570) than those between the two instruments, but still not acceptable. Carryover of WBC, RBC, HGB, HCT, and platelets for open and closed tube sampling, as assessed by the method of Broughton [4], was <1%.

A sample stability study showed that all RBC parameters were stable for 12 h [5]. After this period, a slight increase in MCV (4.5%/48 h), and a fall of RBC (5.5%/48 h) and HCT (constantly for 48 h) were observed. A gradual loss of platelets starting after 6 h was 4.7% at 12 h and 8.5% at 48 h. WBC count was constant for 24 h; after 48 h, an increase by 3.7% was observed. Neutrophil and lymphocyte percentages remained stable for 8 h. After this period, a pronounced decrease in neutrophils and an increase in lymphocyte percentages were observed [6, 7]. The mid-cell fraction was less stable; after 6 h, an increase by 19.6%, and, after 48 h, an increase by 96.6% was observed. Samples with leukocytosis or leukopenia showed a similar time stability as those with leukocyte count within the normal range.

[FIGURE 2 OMITTED]

Linearity determined by serial dilutions of three separate samples selected to cover the clinically important ranges indicated the counter to be linear for HGB concentration for up to 210 g/L, leukocyte count for up to 35 X [10.sup.9]/L, and platelet count for up to 900 X [10.sup.9]/L.

On testing the instrument reliability of leukocyte differentiation by the CD 1700CS, leukocyte three-part differential was compared with manual differentials as a reference method differentiating 400 cells from 269 patient samples [7,81. The linear regression analysis of lymphocytes, mid-cells, and granulocytes, presented in Fig. 2, showed satisfactory correlation coefficients for granulocytes (r = 0.924) and lymphocytes (r = 0.939), whereas the correlation coefficient for mid-cell fraction was notably lower (r = 0.435). A good relation between two technologists was observed, with correlation coeficient for granulocytes and lymphocytes of r = 0.983 and r = 0.985, respectively, but lower for the mid-cell fraction (r = 0.677), indicating the presence of technologist-to-technologist variability for eosinophil, basophil, and monocyte subpopulations calculated from the manual differential as mid-cell fraction. According to our experience, one of the problems of intertechnologist variance for monocytes could be attributed to an unequal distribution of monocytes in the blood smear and to a low number (percentage) of monocytes in the blood smear [9,10].

Sensitivity and specificity of the three-part differentials produced by the analyzer were assessed by analyzing the results of manual differentiation and instrument differentiation [11-13]. Each of 269 samples was classified as truly negative (TN), denoting a differential blood count within the reference range by both methods; truly positive (TP), denoting a differential blood count signalized by the analyzer as pathologic, which was confirmed by manual differentiation; falsely positive (FP), denoting a result signalized by the analyzer as pathologic, whereas on manual differentiation it showed no deviations from a sample of a healthy subject; and falsely negative (FN), denoting a differential blood count result that the analyzer failed to signalize as pathologic, whereas on manual differentiation the sample was found to be pathologic. Of 269 samples tested, 175 (65.1%) samples yielded TP results, 70 (26.0%) samples yielded TN results, 9 (3.3%) samples yielded FP results, and 13 (5.6%) samples yielded FN results. The causes of FN results (n = 13) obtained by the instrument were a failure in signalizing increased granulocytes in three cases, increased granulocytes with left shift in two cases, increased monocytes in four cases, increased eosinophils in two cases, decreased lymphocytes in two cases, and increased lymphocytes in two cases. Analysis of FP results showed that the analyzer falsely signalized increased mid-cell fraction in four cases, increased granulocytes in three cases, decreased granulocytes in one case, and decreased lymphocytes in one case.

Suspect population flags for three-part differential were also evaluated by comparing the instrument flagging with manual differential results [14]. Each sample was analyzed in relation to suspect flags (RO, R1, R2, R3, R4, RM) as indicators of possible distribution and (or) morphological leukocyte abnormalities. Suspect flags were found in 113 (42%) of the total number of samples (n = 269) tested for differential comparability. Of 113 samples flagged, 90 (79.6%) samples showed TP flags. Comparison with the microscopic method confirmed the presence of a distribution and (or) morphologic abnormality in these cases. Of 113 samples flagged, only 8 (7.1%) samples showed FP flags. In these cases, a differential blood count obtained by the analyzer produced suspect population flags, whereas on manual differentiation it showed no deviation from a sample of a healthy subject. Furthermore, 15 (13.3%) samples confirmed by microscopic examination as morphologically abnormal were not flagged by the instrument, so these samples showed FN results related to the instrument flagging system. Among leukocyte flags, the "lymphocyte area anomaly" was most common. Lymphocyte R2 or RM alerts were found in 31 cases, indicating the presence of blasts, variant lymphocytes, lymphopenia, and lymphocytosis. Lymphocyte RO or RM alerts indicate interference to the left of the lymphocyte peak. These alerts were found in 4 cases and referred to the presence of nucleated red cells. Lymphocyte R1 or RM alerts were found in 18 cases and indicated lymphocytosis or lymphopenia. Mid-cell R2 or RM alerts are prompted by interference between the lymphocytes and mononuclear areas secondary to eosinophilia, monocytosis, or blast cells. These alerts were found in 7 cases. Mid-cell R3 or RM alert was found in only one case and indicated the presence of blast cells. Granulocyte R3 or RM alert was found in 22 cases. These alerts were caused by immature granulocytes, band cells, granulocytosis, and neutropenia. Granulocyte R4 or RM alert was found in 13 cases and indicated granulocytosis or neutropenia. Two different flags were found in 17 cases, indicating the presence of distribution and (or) morphological abnormalities for two different leukocyte subpopulations. Reliability of the suspect flags generated by the instrument as detectors of leukocyte morphological abnormalities suggested an 85.4% reliability of the flags for immature granulocytes or left shift, 57% for nucleated RBC and atypical lymphocytes, and 80% for blast cells.

Differential leukocyte count maintains diagnostic significance in two fields: (a) measurement of the relative proportions of normal leukocyte populations, with important implications, for instance, in the diagnosis and monitoring of infectious diseases and in monitoring of cytotoxic therapies; and (b) search for and definition of abnormal cells in the peripheral blood. It is related to the diagnosis of hematologic disorders and requires good test sensitivity for identification of abnormal cells [15]. When the analyzer is used in hospital laboratories that give simultaneous access to healthy subjects and those with widely varying pathologies, it is important to know the percentage of samples submitted to microscopic control. The advantages of automated differential count over manual differentiation using 100 or 200 cells are greater analytical precision, because the differential leukocyte count obtained by the analyzer is performed by counting thousands of cells instead of hundreds and is accompanied by excellent accuracy, at least for neutrophils and lymphocytes, and reduction in costs and turnaround time due to high throughput [15]. The simultaneous production of leukocyte histograms and suspect flags is also an aid to the interpretation of differential blood counts produced by the instrument. Nevertheless, the usefulness of the differential blood count obtained by the analyzer is limited in cases of acute infective processes, hematologic diseases, and allergic states accompanied by changes in hematologic parameters. In these cases, only microscopic differentiation can produce the finding of differential blood count with certainty. This evaluation showed that the CD 17000S analyzer is reliable in separation of normal and pathologic differential blood counts.

In conclusion, the Cell-Dyn 17000S automated hematology analyzer is a suitable and reliable blood counter for complete blood count determination in daily routine. The three-part differential blood count with simultaneous production of leukocyte histograms and interpretative suspect flags can be used for screening and separation of normal and pathologic differential blood counts, thereby considerably reducing daily manual differentiation, in case of normal samples free of distribution and morphological alterations in leukocyte populations. This is a substantially time- and material-saving method as compared with the manual method, at the same time allowing the laboratory personnel to thoroughly examine and follow the samples indicated or found to be pathologic. The analyzer should not be expected to completely replace manual determination and interpretation of differential blood count. Therefore, microscopic analysis of the differential blood count and morphological knowledge will continue to be very important in hematology.

We are indebted to Abbott Diagnostics for technical assistance, to the Ministry of Science and Technology for partial financial support, and to Antonija Redovnikovic for her help in editing the manuscript.

References

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Sandra Petani, Elizabeta Topic, * Graciela Turcic, and Mathias Daschner (Clin. Inst. of Chem. Hematol. Lab., School of Med., Sestre milosrdnice University Hosp., Zagreb, Croatia; * address for correspondence: Clin. Inst. of Chem., Sestre milosrdnice University Hosp., Vinogradska 29, 10.000 Zagreb, Croatia; Fax + 385 1 57 27 30)
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Title Annotation:Technical Briefs
Author:Petani, Sandra; Topic, Elizabeta; Turcic, Graciela; Daschner, Mathias
Publication:Clinical Chemistry
Date:Jun 1, 1997
Words:2726
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