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

objectiveTo generate normative data for thyroid stimulating hormone (TSH) levels in heel prick samples collected from newborns from 24 h to 7 d of age.

methodsFive 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 24 h 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 6 h intervals. Another category placed was division into 24-72 h category, 73-96 h and 99-168 h. Percentile charts were calculated across these specified intervals.

resultsSamples 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 48 h, 23,983 between 49 to 72 h and 30,883 were collected after 72 h. The mean TSH concentration demonstrated a steady decline from 24 h to 168 h. 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.

conclusionsThis 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.