Variables that may affect a result:

Analytical There are two factors can affect the result of a blood test, analytical or physiological. Analytical error is caused by the service, typically the machine or process which produces the result. Physiological error is caused by people, typically how the blood is collected, whether the patient was fasted or taking medication.

 Analytical sensitivity and specificity

 Each blood test will have an experimental technique to produce the result. Confusingly, two sets of sensitivity and specificity exist in blood sciences; they have totally different meanings and refer to either analytical and physiological (or diagnostic) measures. Analytical sensitivity refers to the detection limit of the experiment. This is the smallest amount of material of interest that the experiment can detect. As technology has developed it is increasingly easier to measure smaller quantities of material, although at small levels the accuracy and precision may be lower and this can be measured using quality control.

Analytical specificity refers to whether any other similar chemicals interfere with the test.