Exercise caution when testing the physically active.

Because exercise is considered normal activity for both healthy individuals and rehabilitating patients, it has been largely disregarded during the interpretation of test results. But according to many health care experts, this preanalytic variable can no longer be ignored.

Leisure-time activity is now well recognized as an adjunct to improved physical health and mental well-being. Elective exercise lowers risks of mortality and cardiovascular disease in both healthy individuals and those recuperating from a chronic disease.[1-5] Health professionals also advocate frequent exercise to reduce osteoporosis, prevent or delay the onset of noninsulin-dependent diabetes mellitus (NIDDM), and lower stress.

The recognition and endorsement of physical activity for health maintenance and rehabilitation for chronic disease introduce a preanalytic variable that must be considered during the interpretation of lab test results. Patient data such as recent food and alcohol intake, pregnancy status, psychological stress, caffeine consumption, cigarette smoking, and drag therapy are typically addressed in lab procedure manuals. According to the CLIA regulations published in the Federal Register ([section]493.1109, subpart f), "The laboratory must make available to clients, upon request, information that may affect the interpretation of test results, such as test interferences."[6] When establishing reference ranges and interpreting lab results, however, information regarding physical activity levels typically has been excluded.

Both clinician and laboratorian must be aware of how exercise effects test parameters. Depending on the time interval between exercise and specimen collection, certain biochemical parameters can be increased by as much as 200 times the reference interval.[7] No wonder accurate reporting of recent physical activities and exercise habits is essential to provide a proper perspective for test interpretation.

* What's happening in the body? A multitude of changes take place in the body as a result of physical activity. First, exercise is associated with activation of the sympathetic nervous system and elevation of plasma norepinephrine and epinephrine concentrations.[8] In response to these hormonal changes, several physiologic alterations occur that increase the delivery of oxygen and metabolic fuels to skeletal muscles for energy production and regulation of homeostatic mechanisms in the body. There is a subsequent release, or suppression, of other hormones that specifically regulate the mobilization of glucose, free fatty acids, and amino acids and regulate electrolyte balance. The magnitude of these shifts in hormones and metabolic fuels is dependent on many factors, including, but not limited to, a patient's sex, age, and recent diet; intensity and duration of physical exertion; and level of training.

Increases in metabolic rate and physiologic changes accompanying exercise are so automatic that they go unnoticed in healthy, physically active people and are thus considered normal occurrences. Under other circumstances, however, these same metabolic changes could suggest the need for medical intervention and trigger further lab evaluation.[9] During maximum physical exertion, for example, a person's metabolic rate may increase 20 times his resting rate. In contrast, an extremely high fever approaching lethal limits may only double the metabolic rate.[10]

Exercise causes relative changes in certain analytes owing to plasma fluid shifts. Acute exercise may cause plasma volume to become greatly reduced, which results in hemoconcentration.[11] In addition, exercise produces changes in the consumption of metabolic fuels, the production of metabolites, and the permeability of cells to proteins and enzymes. Furthermore, osmotically active metabolites like potassium, phosphate, and lactate will accumulate in tissue spaces and draw water from the capillaries. The combined effects of these relative and absolute changes in blood and urine analytes can be detected 24 to 72 hours later.[12]

* Acute exercise. All biochemical parameters have the potential to be altered during and immediately following exercise. The observed metabolic response to exercise is related to the rise in glucagon, growth hormone, catecholamines, prolactin, adrenocorticotropic hormone (ACTH), cortisol, luteinizing hormone, progesterone, antidiuretic hormone (ADH), angiotensinogen, aldosterone, renin, atrial natriatic factor, thyroid stimulating hormone (TSH), thyroid hormones ([T.sub.3] and [T.sub.4]), parathyroid hormone, estradiol, and beta endorphins. One notable exception is insulin, which declines in proportion to exercise intensity.[7] (This decrease will be eliminated, however, after a brief recovery period of about 30 minutes.[12]) Literature on short-term hormonal responses to exercise seems to conclude the residual effects of rises and falls in plasma hormones stop within 2 hours after exercising.[7,12]

While studies on the effects of acute exercise on plasma lipids, lipoproteins, and apolipoproteins abound, discrepancies exist regarding the short-term impact of exercise on these parameters. Because work intensity and duration of an exercise session correlate with related changes in the lipid profile, these influences are important variables to consider when assessing lab findings The most profound and consistent effect of acute exercise on the lipid profile is the significant decrease in plasma triglycerides, which occurs 12 to 24 hours following an exercise session. Alteration in basal triglycerides, however, may last up to 72 hours following exercise.[13]

The magnitude to which plasma triglycerides will decrease is also highly dependent on pre-exercise values. Simply stated, hypertriglyceridemic individuals show the most exaggerated decline in triglycerides given the same exercise workload. Serum total cholesterol and LDL cholesterol may drop following acute exercise. Similarly, a rise in HDL cholesterol, a fall in apolipoprotein (apo) AI, or a decline in apo B may (or may not) be detected. With the exception of triglycerides, lipid and lipoprotein alterations attributed to acute exercise typically return to baseline 24 to 48 hours after exercise.[7,12]

Many studies also are available on the influence of acute exercise on serum enzymes. In fact, earliest reports of these findings date back to the 1950s. Still, there is considerable individual variability in the degree to which serum enzymes increase after exercise. Much depends on the duration of someone's physical exertion, how long after an exercise session a blood specimen is drawn, the physical fitness of that individual (his training state, that is), and the athlete's age and gender. An increase in serum enzymes following intense or prolonged exercise may be so significant it could lead the physician to an erroneous diagnosis of organ-specific damage such as an acute myocardial infarction.[14]

Although creatine kinase (CK) is the most sensitive marker of microtrauma to skeletal muscle, serum enzymes such as lactic dehydrogenase (LD), aspartate aminotransferase (AST), alanine aminotransferase (ALT), aldolase, acid phosphatase (ACP), alkaline phosphatase (ALP), and gamma glutamyl transferase (GGT) also may rise above their respective reference ranges following physical exertion.[7]

Extraordinary physical stress, such as marathon running, can also elevate CK-MB. While an increase in the serum CK-MB fraction is probably due to a skeletal muscle source in these cases, a physician must rely on additional diagnostic criteria before ruling out acute myocardial infarction. Baseline or "resting" serum enzyme values (especially CK) will be higher in physically active people than in their sedentary counterparts. To get an accurate clinical lab picture of a physically active patient, the person usually needs to abstain from exercise 4 to 5 days before testing.

Intense lengthy exercise also influences the amount of protein found in the urine. One of the most dramatic preanalytic effects of exercise on test results is exercise-induced proteinuria. As workout intensity increases, the amount of protein, especially albumin, increases accordingly. Exercise-induced proteinuria is a benign condition that disappears within 24 hours following exercise stress; however, this phenomenon can contribute to a positive bias when testing for urine protein. Patients being screened for microalbuminuria should refrain from exercising at least 24 hours before urine collection.

Further, vigorous exercise can lead to myoglobinuria and hematuria. Some people who incur major skeletal trauma from severe exercise release myoglobin from the traumatized muscle. Myoglobinuria may be detected up to 48 hours later (sometimes longer) following the trauma.[7] While hemoglobinuria is rare following exercise, people can test positive on a urine dipstick, indicating the possible presence of red blood cells, hemoglobin, or myoglobin.

Hematocrit and leukocytes increase with exercise, reaching their highest levels near maximal metabolic activity. Subsequently, as a result of exercise-induced inflammation and fluid shifts, further rebound increases in leukocytes and a decrease in hemoglobin may occur 4 to 18 hours after exercise.[9] Other alterations, notably in acute phase proteins, may also accompany these delayed changes.

Waller published an extensive review on the effects of short-term exercise on immunologic tests.[15] Short-term exercise appears to both enhance and suppress the immune system simultaneously. Nonspecific host defense responses include an elevation in the total lymphocyte count, absolute number of T cells, natural killer cells, complement activation, and increased granulocytic and monocytic number and function. Conversely, immunosuppressive responses are host-specific and include decreases in percentages of CD3 and CD4 cells, CD4/CD8 ratio, lymphoblast transformation, and salivary IgA and IgM. While the extent of these immunologic responses vary, depending on the intensity and duration of the exercise, most responses last less than 2 hours.[15]

Exercise also has been shown to produce changes in hemostatic function tests that reflect both in vitro hypercoagulability and increased fibrinolytic activity.[16] Vigorous exercise consistently results in decreasing activated partial thromboplastin time (APTT) and whole blood clotting time, and increasing Factor X and VIII complex proteins.[7,16] These changes persist for 1 hour after exercise. Fibrinolytic activity (plasmin activity), on the other hand, consistently has been reported to be enhanced following physical activity. The rise in fibrinolytic activity seems to be related to both intensity and duration of an exercise session.[16] An increase in fibrinolytic activity has been shown by increased levels of tissue plasminogen activator (tPA), decreased euglobulin lysis time, increased fibrin plate lysis, increased fibrin degradation products (FDPs), increased alpha-2 plasmin inhibitor-plasmin complexes, decreased plasminogen, and increased degradation of alpha chains of fibrinogen. These markers persist up to 1 hour post-exercise.

Platelet function is also altered in vitro following exercise, but controversy surrounds the overall effect of these hemostatic events. Researchers have shown increases, decreases, or no change in platelet aggregation following acute exercise. These inconsistencies may be attributed to the variety of methods used to determine platelet aggregation, differences in exercise protocols, and individuals' fitness status.[7,16] Overall, acute exercise leads to a temporary increase in blood coagulability, fibrinolytic activity, and platelet activity in trained and untrained individuals.[17]

* Chronic exercise. Physical training (repetitive bouts of exercise over a specific period of time to develop physical fitness) has been demonstrated to reduce the risk of developing NIDDM.[18] Because regular exercise can reverse insulin resistance, it also can prevent the sequence of events that result in clinical disease.

The most profound and consistent effect of physical training on glucose metabolism is the lowering of plasma insulin at rest.[7] Overweight individuals with a family history of NIDDM show improved glycemic control after exercise training. Positive changes reported include decreased fasting or random blood glucose, an improved oral glucose tolerance test, and decreased plasma insulin. Likewise, NIDDM patients who exercise aerobically at 50 to 70% of maximal V[O.sub.2] uptake for 20 to 45 minutes at least 3 times a week for 6 to 10 weeks typically show a 10 to 20% decrease in glycohemoglobin (hemoglobin [A.sub.1c]).[18]

Exercising to improve blood glucose control in insulin-dependent diabetes mellitus (IDDM) patients remains controversial. Such patients who are athletes or who enjoy leisure-time exercise must follow supervised exercise programs to avoid episodes of clinically significant hyper- or hypoglycemia, which could occur during an exercise session. These patients may safely participate in recreational or competitive sports but must adjust diet and insulin doses accordingly.

Both NIDDM and IDDM patients, as well as nondiabetic individuals, can diminish cardiovascular risk factors through regular exercise. Large epidemiologic studies of the general population suggest individuals who increase their physical activity decrease their risk for premature coronary artery disease. A sustained program of regular aerobic exercise will consistently lower serum triglycerides and improve the lipid/lipoprotein profile by raising HDL cholesterol, lowering LDL cholesterol, raising apo AI, and lowering apo B.[7]

The effect of gravity on bone mass maintenance has been extensively examined in conjunction with prevention of osteoporosis and the unique challenges of the Space Age. Calcium studies conducted on Skylab 4 astronauts demonstrated an astronaut could lose calcium in excess of 25% of the calcium pool in 1 year.[19] Numerous prospective and cross-sectional studies have shown bone density is increased at selected sites following a regular program of weight-bearing exercises such as high-impact aerobics and jogging.[20] Increased bone density reduces the risk of osteoporotic fractures.

Data are sparse but meaningful regarding evidence linking exercise and improved host-defense outcomes (reduced risk of cancer and infection). It appears exercise may exert a clinically significant although perhaps indirect protective influence on cancers of the colon, breast, and reproductive tract.[21]

Data are less clear on the relationship between exercise and immunity/infection. Retrospective studies of competitive athletes have revealed more frequent episodes of upper respiratory infections during training. Exercise contributes to an increase in the same stress hormones (cortisol, epinephrine, norepinephrine, and endorphins), which are also released into the bloodstream during infection and psychological stress. In practical terms, strenuous exercise may do more harm than good in people with an infection.

Though exercise training produces many health-related benefits, people who participate in an exercise program too intense or rapidly progressive for their age or physiologic state may experience clinically significant reproductive hormonal changes. Females who over-train, for instance, can disrupt their menstrual cycle, causing delayed menarche, a shortened luteal phase, and secondary amenorrhea.[22] Negative calcium balance is subsequently associated with low gonadal steroid activity in female athletes with secondary amenorrhea.[22] A decrease in exercise intensity, oral calcium supplements, and possible estrogen and progesterone therapy will reduce osteoporosis risk in these females.

The male equivalent of exercise-induced amenorrhea is suppressed spermatogenesis with reduced sperm counts and decreased serum testosterone.[22] Cross-sectional data suggest decreased semen volume, semen quality, and fertility may occur in some athletes.[23] Disruptions in the female and male reproductive hormones that may occur in the overtrained athlete are reversible, although long-term health implications of these changes are unclear.

* Where the lab fits in. Understanding the effects of exercise on lab parameters can only enhance the interpretation of patient results. As such, a complete patient history, including exercise habits, must be available to laboratorians during their interpretation of results.

Our involvement in this endeavor must not end there. Lab procedure manuals must include not only statements regarding the effects of both acute and chronic exercise training on all test parameters but also standardized specimen collection protocols for all lab parameters. Laboratory procedures should be updated annually to reflect current exercise research findings. In addition, patients must be given strict instructions on how long to abstain from exercise before specimen collection. A number of useful references are available to help laboratorians write their procedure manuals, among them, Donald S. Young's Effects of Preanalytical Variables on Clinical Laboratory Tests (AACC Press, Washington, D.C., 1993).

References

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2. Leon AS, Connett J, Jacobs DR, Rauramaa R. Leisure-time physical activity levels and risk of coronary heart disease and death: The multiple risk factor intervention trial. JAMA. 1987; 258: 2388-2395.

3. Chazan BI, Balodimos MC, Ryan JR, Marble A. Twenty-five to forty-five year diabetics with and without vascular complications. Diabetologia. 1970; 6: 565-569.

4. Dorman JS, Tajima N, LaPorte RE, et al. The Pittsburgh insulin-dependent diabetes mellitus (IDDM) morbidity and mortality study: Case control analyses of risk factors for mortality. Diabetes Care. 1985; 8(Suppl 1): 54-60.

5. Kriska AM, LaPorte RE, Patrick SH, Kuller LH, Orchard TJ. The association of physical activity and diabetes complications in individuals with insulin-dependent diabetes mellitus: The epidemiology of diabetes complications study - VII. J Clin Epidemiol. 1991; 44: 1207-1214.

6. Clinical Laboratory Improvement Amendments of 1988; Final Rule. Federal Register. 57(40): Feb. 28, 1992; 7162-7163.

7. Ward KM. Chemistry of exercise. In: Anderson SC, Cockayne S, eds. Clinical Chemistry: Concepts and Applications. Philadelphia, Pa: W.B. Saunders Company; 1993: 634-651.

8. Bouchard C, Shepard RJ, Stephens T, Sutton JR, McPherson BD. Exercise, fitness and health: The consensus statement. In: Bouchard C, Shepard RJ, Stephens T, Sutton JR, McPherson BD, eds. Exercise, Fitness and Health. Champaign, Ill: Human Kinetics Books; 1988: 7-9.

9. Neisler HM. The effects of exercise on laboratory tests: An overview. Clin Lab Sci. 1991; 4(3): 164-167.

10. Ganong WF. Review of Medical Physiology. 17th ed. Norwalk, Conn: Appleton and Lange; 1995: 64-65, 256-258.

11. Van Beaumont W, Greenleaf JE, Juhos L. Disproportional changes in hematocrit, plasma volume, and proteins during exercise and bedrest. J Appl Physiol. 1972; 33: 55-61.

12. Ward KM. Exercise: A preanalytic source of variation in clinical chemistry test results. Clin Lab Sci. 1991; 4(3): 168-174.

13. Schneider SH, Vitug A, Ruderman N, Phil D. Atherosclerosis and physical activity. Diabetes Metabol Rev. 1986; 1: 513-553.

14. Apple FS, McGue MK. Serum enzyme changes during marathon training. Am J Clin Pathol. 1983; 79: 716-719.

15. Waller KV. Effects of short-term exercise on immunologic tests. Clin Lab Sci. 1991; 4[3]: 175-180.

16. Rudmann SV, Marble TL. Effects of physical exercise on laboratory measurements of hemostatic function. Clin Lab Sci. 1991; 4(3): 181-185.

17. Sinzinger H, Virgoloni I. Effects of exercise on parameters of blood coagulation, platelet function, and the prostaglandin system. Sports Med. 1988; 6: 238-245.

18. Baraz L, Schneider SH. Exercise and diabetes. Clin Diabetes. 1994; July/August: 94-98.

19. Wheton GD. Disuse osteoporosis: Physiological aspects. Calcif Tissue Int. 1984; 36(Suppl): 146-150.

20. Tipton CM, Vailas AC. Bone and connective tissue adaptations to physical activity. In: Bouchard C, Shepard RJ, Stephens T, Sutton JR, McPherson BD, eds. Exercise Fitness and Health. Philadelphia, Pa: W.B. Saunders Company: 1993; 331-344.

21. Simon HB. Discussion: Exercise, immunity, cancer, and infection. Exercise, Health and Fitness. Champaign, Ill: Human Kinetics Books; 1988; 581-588.

22. Sutton JR, Farrell PA, Harber VJ. Hormonal adaptation to physical activity. In: Bouchard C, Shepard RJ, Stephens T, Sutton JR, McPherson BD, eds. Exercise, Fitness and Health. Champaign, Ill: Human Kinetics Books; 1988; 217-257.

23. Ayers JWT, Komesu Y, Romani T, Ansbacher R. Antropomorphic, hormonal, and psychologic correlates of semen quality in endurance-trained athletes. Fertil Steril. 1985; 43: 917-921.

Kory M. Ward, Ph.D is associate professor, School of Allied Medical Professions, Ohio State University, Columbus, Ohio.