No abstract

Pre-existing researches have shown that some biochemical machinery reveal diurnal variation and are perceptive to postural change. The latter is due to the consequence of gravitational force and hydrostatic pressure on the plasma level. Therefore laboratories are suggested to apply the rules of standardization based on preanalytical factors, which state that blood samples should be taken in the morning after at least 15 minutes of rest. The concentrations of many substances in blood vary considerably at different times of day e.g. Cortisol (8:am at peak and 4:00 pm dropped) Specimens for these analyses must be collected at the times specified by the laboratory, as there may be no reference ranges relating to their concentrations in blood at other times According to current recommendations, blood samples should be taken in the morning after 15 minutes' resting time. Multiple blood and saliva cortisol levels collected at different times, such as at 8 am and 4 pm, have been used successfully to evaluate both cortisol levels and diurnal variation. A 24-hour urine cortisol sample will not show diurnal variation; it will measure the total amount of unbound cortisol excreted in 24 hours. The heart service of any clinical laboratory is blood sampling and analysis. In connection with this, reference intervals or decision limits need to be established. Some components exhibit diurnal variation and impact of resting time prior to blood sampling on biochemical components, including albumin, thyrotropin (TSH), total calcium and sodium in plasma.