A plethora of additional factors can affect your test results: the time of day you have your blood sample taken, your intake of caffeine, tobacco, alcohol, and vitamin C; your diet (vegetarian vs. meat eaters); 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 concentrations can increase a little when moving from lying down to an upright position. Vigorous exercise can affect concentrations of creatine kinase (CK), cholesterol, aspartate aminotransferase (AST), and lactate dehydrogenase (LD).

All these considerations show the significance of taking blood or urine samples in a standardised fashion for performing and interpreting laboratory tests. It’s important to follow your doctor’s instructions when preparing for your tests, such as coming in first thing in the morning and getting your blood taken before you eat anything.