The use of critical levels of birth weight and "free bilirubin" as an approach for prevention of kernicterus.

Free bilirubin (FB) and total bilirubin (TB) were determined in 154 samples of blood taken from 112 jaundiced newborns: 51 prematures without hemolysis (19 of these with RDS); 26 full terms presenting ABO incompatibility; 35 newborns (both prematures and full terms) presenting rhesus incompatibility. Kernicterus was observed in seven cases and only three occurred in the TB group above 20 mg/100 ml; 57 cases had FB equal to or above 0.1 mg/100 ml and all kernicterus fell into this category. In the other 55 cases in which FB was less than 0.1 mg/100 ml no kernicterus was observed. In the group of healthy full-term newborns presenting ABO incompatibility, 15 had FB above or equal to 0.1 mg/100 ml ranging between 0.1 and 0.4 mg/100 ml; however no kernicterus was observed during the neonatal period. On the contrary, in the group of prematures a little more than half of the cases had a FB ranging from 0.1 to 0.4 mg/100 ml whereas four macroscopic kernicterus cases were observed. The difference between the two groups compels us to consider other factors than those acting on the albumin-bilirubin binding especially those acting on the blood-brain barrier and on the fixation of the pigment by the neurons. A second series of 605 consecutive autopsies, on a period of 10 years, on prematures excluding light-for-dates and cases of hemolysis, evaluates the distribution of 40 kernicterus as a function of birth weight. On this second series kernicterus appears with maximal frequency for birth weight between 1,000 and 1,250 g, with a nonnegligible frequency at 1,500 to 2,000 g and was absent between 2,000 and 2,500 g. 13 kernicterus were observed for a peak TB below 12 mg/100 ml. These results seem to justify a systematic determination of FB in the premature weighing less than 2,000 g from the 24th hour of life whether he has jaundice or not.