Measurement of serum alpha-fetoprotein in early infancy: utilization of dried blood specimens.

Serum alpha-fetoprotein (AFP) concentrations were measured in dried blood spots and the biologic half-life of AFP was determined during the first month after parturition. AFP blood levels, in babies at all birthweight groups during the first wk, were partitioned according to birthweight and sex. A synthetic surge of serum AFP at postnatal day 3 was observed in babies of the low birthweight category (less than 6 lb 8 oz), whereas a concomitant surge could not be demonstrated in babies of medium, (6 lb 8 oz to 8 lb 8 oz), and high birthweight, (greater than 8 lb 8 oz), categories. All babies weighing less than 6 lb 8 oz, regardless of prematurity likewise displayed the synthetic surge. The sex of the infant appeared to have no influence on AFP serum concentrations. In a population of infants ranging in age from 1-30 days, the biologic apparent half-life of AFP was calculated as 5.7 days; however, the half-life of AFP was found to differ among the three groups of infants when subdivided by birthweight and was higher (7.7 days) in babies of low birthweight. Our determination of 2 S.D. cutoff values for AFP in the first wk of life should prompt further studies in which the relationship of AFP to newborn disorders should be more fully explored.