Normative Data for Thyroid Stimulating Hormone for Screening of Congenital Hypothyroidism.

Abstract

To generate normative data for thyroid stimulating hormone (TSH) levels in heel prick samples collected from newborns from 24h to 7 d of age. Five regional laboratories were designated as the testing laboratories. Dried blood spots (DBS) from babies (> or = 34 wk of gestation) were collected by heel prick at least after 24h and within seven days after birth. TSH estimation was done using time resolved fluoroimmunoassay. Values above 20mIU/L were labelled as presumptive positive. Hour interval specific normative data was categorized at 6h intervals. Another category placed was division into 24-72h category, 73-96h and 99-168h. Percentile charts were calculated across these specified intervals. Samples analysed were 104,006 collected cumulatively from the 5 centers. Of the total samples analysed for TSH, 92.8% had values less than 5 mIU/l. When TSH values were interpreted with respect to time, a steady decrease with time was observed. Of the babies' samples, 48,839 were collected between 24 and 48h, 23,983 between 49 to 72h and 30,883 were collected after 72h. The mean TSH concentration demonstrated a steady decline from 24h to 168h. It is apparent that 10 mIU/l is the 97.5th percentile value even when corrected for gender, birth weight and age at sampling. Thus 10 mIU/l seems to be the right cutoff beyond which a second sample should be sought. This is the largest series reported with a broader population mix with representations of both urban (including slums) as well as a rural population. As this study excluded preterm babies, the utility of cut offs generated is not applicable to this subset and also to critically sick neonates. However, this study gives a true representation of the normative values for majority of the newborns born at term with weight appropriate for the gestation.