The Effect of Diurnal Variation on Laboratory Tests

Abstract

Objective: Commonly used biochemical tests in blood samples may be measured at any time of day. This study investigated the existence and clinical significance of diurnal variations in some of routine parameters to facilitate accurate and reliable decision-making in diagnosis and follow-up. Materials and Methods: Blood samples were collected from 17 healthy volunteers who were 18-50 years of age (11 men, 6 women) on the same day at 9:00 am, 12:00 am, 3:00 pm, 6:00 pm, and 12:00 pm. Samples collected at 9:00 am were regarded as baseline. The results of 19 biochemical parameters in blood samples obtained at 12.00 am, 3.00 pm, 6.00 pm and 12.00 pm were statistically and clinically compared with the results at 9.00 am baseline sample. Results: Total protein, creatinine, aspartate transaminase, alanine transaminase, alkaline phosphatase and gamma glutamyl transferase showed no clinically significant variation within the day, but clinically significant changes were observed in levels of glucose, total cholesterol, HDL-cholesterol, triglyceride, total bilirubin (TBIL), direct bilirubin (DBIL), albumin, blood urea nitrogen, uric acid, sodium, potassium, chloride and amylase. Especially, BUN changed by maximum 20-30%, TBIL, DBIL and triglyceride maximum 40-50% within the day. Conclusion: The results of our study suggest that clinicians should consider the timing of blood sampling and the diurnal variations in BUN, TBIL, DBIL and triglyceride parameters during diagnosis and treatment follow-up. Sampling throughout the day seems to pose no problem for other tests with limited diurnal variation.