An important component of an immunoassay is the sample. The versatility of immunoassays permits the measurement of hormones in almost every biological fluid. Serum, plasma, urine, saliva, spinal or amniotic fluid, or even whole blood that has been dried on filter paper, are all sample materials that can be used in immunoassays.
The conditions under which a sample is drawn, however, can influence the results of the immunoassay to a great extent.
Many hormones are secreted in pulsatile manner and/or with a circadian rhythm; others are influenced by factors such as stress or food intake. Thus, correct interpretation of laboratory results is highly dependent on sampling time and conditions: for example, blood sampling for the measurement of cortisol should always be carried out at a certain time of day and under rested conditions.
