Preterm infants with high plantar blood collection index may be normal phenomenon, or there may be some congenital diseases. 1. Normal phenomenon: affected by a variety of factors, preterm infants plantar blood test may be inaccurate, many preterm infants can be reexamined again to return to normal values, if two consecutive reexaminations are within the range of normal values, it is considered to be normal. 2. Existence of congenital diseases: Plantar blood collection is mainly for screening some congenital diseases, such as phenylketonuria, hypothyroidism, G6PD enzyme deficiency, adrenocortical hyperplasia and so on. Any high index should be taken seriously, and if the index continues to increase or does not decrease when the test is repeated, early intervention is needed. Preterm infants with a high PSI should be taken seriously, and should be reviewed regularly as prescribed by the doctor. If the PSI is still high after two or more reviews, genetic testing can be performed, and early intervention should be made if there is a problem.