Reference Interval of Thyroxine and Thyroid Stimulating Hormone in Cord Blood in Tertiary Care Hospital, Kerala

Abstract

Introduction: Even though Congenital hypothyroidism (CH) is one of the most common causes of preventable mental retardation, diagnosis at birth is difficult due to absent or delayed clinical manifestations, owing to the transplacental transfer of maternal thyroid hormones. Delayed diagnosis and treatment can cause irreversible damage to the developing brain. The occurrence of cognitive dysfunction due to CH has reduced significantly in countries where Newborn Screening (NBS) is routinely practiced. Cord blood screening is considered to be an effective method to diagnose congenital hypothyroidism. Aim: To establish reference interval for thyroxine (T3 and T4) and Thyroid Stimulating Hormone (TSH) in cord blood Medical College, Thrissur. Materials and Methods: In the present cross-sectional observational hospital based study, the cord blood samples from 252 deliveries collected over a period of three months from May 2011 at in Government Medical College, Thrissur, Kerala, India. A 5 mL of cord blood samples were collected in a plain non vacuum tube with clot activator from umbilical cord incised 15-20 cm at the time of birth. T3, T4 and TSH was estimated by Enzyme Linked Immuno-sorbent Assay (ELISA) using kits of ELISA reader and Washer. Normality check done by visual inspection of histogram, Q-Q plot, box plot and Kolmogorov-Smirnov test. Results: In total of 153 cord blood samples considered, and final analysis was done on 151 samples (69 males and 82 females) after excluding the samples of babies delivered by Lower Segment Cesarean Section (LSCS). The gestational age was mean 38.48 weeks and mean age of mothers was 24.22 years. More than 90% of the values for TSH is less than 12 mIU/mL and 90% of T4 values is less than 20 µg/dL. Reference interval determined by non parametric ascending rank order. Reference interval established is 0.63-17.033 mIU/L and 9.45-27.173 for TSH and T4 respectively, lower than those reported from studies in other parts of India. The mean value of TSH was 5.084 mIU/L and 87.5% of babies are having TSH values <10 mIU/L. Conclusion: The study was conducted to establish reference intervals for cord blood TSH, T4 and T3 and confirms to the use of cut off values for the screening of CH for TSH as >20 mIU/L.