Application of Nonisotopic Immunoassay to Neonatal Screening

During the past 20 years, neonatal screening programs using the Guthrie test for inborn errors of metabolism such as phenylketonuria have become more widely used. The characteristics of diseases in which mass screening is 

Because the irreversible mental retardation caused by neonatal hypothyroidism can be prevented by early treatment with thyroid hormone, the importance of early diagnosis of this disease has been emphasized. The difficulty of its early diagnosis by clinical features alone and its relatively high incidence have prompted the organization of various mass screening programs that include measuring thyroxine (T4) (D5) or TSH (13, Mil) by radioimmunoassay. 

Serum samples obtained from cord blood can be used, but small amounts of blood can be taken easily on filter paper by heel puncture and the dried blood sample on filter paper (blood disks) can be sent to special laboratories by mail. Therefore, the latter method is now widely used in neonatal screening programs. 

In 1976, we developed a double-antibody enzyme immunoassay of TSH using alkaline phosphatase, but this method was not very sensitive (M8). As shown in Table 10, several other methods were later reported (A3, 12, K2, K3, M7) and two methods have been used to measure TSH in dried blood samples in screening for neonatal hypothyroidism in Japan. 

One is a competitive double-antibody solid-phase method using perox-idase/TSH conjugates, which was reported by Kato et al. (K3). Their pilot study on mass screening for neonatal hypothyroidism has been successful. 

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