The Impact of Endurance Exercise on Routine Laboratory Parameters in Young Trained Individuals

<b>Background</b>: Endurance effort aims to improve aerobic capacity. During physical exertion, fluid shifts from intravascular to interstitial spaces, affecting potential conclusions from laboratory test results. The study aimed to assess the effects of endurance exercise on clinical interpretations of routine laboratory hematological and biochemical diagnostic tests. <b>Methods</b>: Participants were young, healthy, and physically active men aged 16-36 and women aged 16-29, who performed progressive treadmill tests to exhaustion. Blood samples were collected before the test, immediately after the test, and after 17 h of recovery. <b>Results</b>: The results showed that endurance exercise led to transient increases in the number of peripheral blood leukocytes and their subpopulations. A direct biological effect of endurance effort was an increase in the activity of amylase, AST, ALT, CK, GGT, LDH, and ALP, as well as in the concentration of creatinine, urea, uric acid, glucose, albumin, total protein, total cholesterol, HDL, triglycerides, sodium, chloride, phosphorus, and iron. Decreases in potassium and calcium (total and ionized) concentrations were also observed. <b>Conclusions</b>: The analyses clearly showed that laboratory tests performed in highly trained individuals may provide interpretation difficulties, and the reference ranges generally accepted in the healthy population might not apply to athletes.