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Reference Ranges and What They Mean

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Other Factors Affecting Test Results

Laboratories will generally report your test results accompanied by a reference range keyed to your age and sex, if appropriate. Your physician then will still need to interpret the results based on personal knowledge of your health status, including any medications or herbal remedies you may be taking. A plethora of additional factors can affect your test results: your intake of caffeine, tobacco, alcohol, and vitamin C; your diet (vegetarian vs. carnivorous); stress or anxiety; or a pregnancy. Even your posture when the sample is taken can affect some results, as can recent heavy exertion. For example, albumin and calcium levels may increase when shifting from lying down to an upright position.

Factors such as occupation, altitude, and distance from the ocean have been known to affect results. Regular exercise can also affect values of certain tests; in particular, levels of creatine phosphokinase (CK), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) will increase. Additionally, testosterone, luteinizing hormone (LH), and platelet levels can increase in people who participate for months and years in strenuous exercise such as distance running and weightlifting.

All these considerations underscore the significance of taking blood or urine samples in a standardized fashion for performing and interpreting laboratory tests (and home tests as well). It is important to comply with your doctor's instructions in preparing for the test, such as coming in first thing in the morning, before you eat anything, to get your blood drawn. That compliance makes your sample as close as possible to others; it keeps you within the parameters of your reference group.

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