Comparison of Primary TSH (pTSH) to Primary T4 with Confirmatory TSH (T4/TSH) Screening for Congenital Hypothyroidism (CH)

Abstract

Our recent survey of 38 states in U.S. & 10 countries indicated that 4.45 million(m) infants were screened for CH by 12/31/79, & 1048 cases of primary hypothyroidism detected (incidence of 1 in 4245) on the 1st specimen. Screening methods varied: (1) T4/TSH: 3.73m, 835 cases, 1 in 4466 incidence; (2) pTSH: 0.5m, 157 cases (1 in 3239); (3) both T4 & TSH: 0.2m, 56 cases (1 in 3695). In summary, programs using pTSH screening detected a higher incidence of CH than programs using T4/TSH screening. When confirmatory TSH is tested on the lowest 10-15% of T4 values, the incidence of CH approaches a maximum comparable to pTSH screening. In programs collecting 2 routine specimens, 169 cases were detected in 0.78m newborn (nb) specimens (1 in 4600) & 22 cases in 0.6m followup(fu) specimens (1 in 26,000). Of the 38 cases of CH that were missed, 12 had normal T4 levels & 4 with primary CH had normal TSH levels. For 3 years we have tested both nb & fu specimens by 2 methods: (1)T4/TSH (TSH test on lowest 3% of T4) & (2) pTSH. Normal TSH is <30 μU/ml of serum in two 3 mm blood discs. 60% of nb specimens were obtained by age 2 days, & the false positive (elevated TSH) rate was 0.9% whereas the rate in nb specimens collected after 2 days & in all fu speicmens was <0.2%, comparable to pTSH cord serum screening. Summary: For specimens collected before 48h of age, higher TSH cutoff levels(30-60μU/ml)must be determined to avoid false positive recall rates,yet identify all infants with CH.

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