EFFECT OF PREANALYTICAL VARIABLES ON SERUM THYROID STIMULATING HORMONE ANALYSIS BY CHEMILUMINESCENCE METHOD

Objective: To identify effect of pre-analytical variables on serum thyroid stimulating hormone. Study Design: Cross sectional study. Place and Duration of Study: Armed Forces Institute of Pathology (AFIP) Rawalpindi, Department of Chemical Pathology & Endocrinology, from Mar 2018 to Aug 2018. Methodology: Hundred subjects with ages ranging from 18 to 34 years, irrespective of gender, were randomly selected for this study. Five milliliters venous blood sample was collected from each subject in a serum separator and divided into two aliquots. First aliquot was centrifuged and analyzed immediately for TSH, while second aliquot was stored for 24 hours and was then analyzed. TSH was measured by third generation assay usingchemiluminescence technique on ADVIA Centaur® XP. Serum TSH levels were also analyzed twice daily; in the morning (0800 to 0900 hours) and afternoon (1400 to 1600 hours). Data was analyzed using SPSS version 24. Frequency and percentages were calculated for qualitative variables like gender and pre-analytical variables. Test of significance Mann-Whitney U-test was applied and p-value <0.05 was taken as significant. Results: Mean age of subjects was 23 ± 3.4 years. Change in circadian rhythm was observed in 17 (28%) males and 14 (36%) females. Statistically significant association was found between morning and evening TSH levels, while no change was observed in TSH level by early and late centrifugation of samples. Conclusion: TSH levels vary significantly between blood samples collected at different timings of the day from the same person. TSH is resistant to degradation, immunologically stable, and reasonably insensitive to potential problems associated with routine specimen handling, when measured by immunoassay technique. Therefore, it is helpful in large epidemiological studies and small size laboratory, which require long transportation time and storage.