Many 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 versus meat eaters); stress or anxiety; or pregnancy. Even your posture when the sample is taken can affect some results, as can recent heavy exercise. For example, albumin and calcium levels can increase a little when you change from lying down to an upright position. Vigorous exercise can affect levels of creatine kinase (CK), aspartate aminotransferase (AST), and lactate dehydrogenase (LD).

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

The type of units used to report results can vary between laboratories. In Australasia and Europe most tests are reported in the units defined by the System Internationale such as moles and litres but in the US, the majority of tests are reported in mass units eg milligram (mg) in volumes of decilitres (dL). The misuse of results and units can result in potentially hazardous mistakes.