Thyroid Stimulating Hormone Immunoassay Using Heel Prick Plasma for Follow-Up Screening of Neonates to Confirm Hypothyroidism

Abstract

A rapid, sensitive radioimmunoassay for TSH is described that requires a whole blood specimen collected by heel prick using an EDTA microhematocrit capillary tube. The technique was adapted from a commercially available kit and allows for hematocrit determination to correct day five T₄ spot screening and low plasma volume assaying (10 μl). The collection procedure is atraumatic to the newborn when compared with the difficulties of venous sampling. This method is also advantageous for small volume venous samples and should be useful for follow-up on recalled newborns for positive diagnosis of neonatal hypothyroidism.