In reply to Nicole Bernshaw's inquiry about the onset of jaundice in a five-week old breastfed infant, this is a difficult query to answer without considerably more information. First, a great deal more data is needed about both the history of jaundice in this family (numbers of people and relationship, duration of jaundice, what laboratory studies they have had, etc.). Second, one must determine whether the infant has an unconjugated (indirect-reacting) or conjugated (direct-reacting) hyperbilirubinemia. Late onset of unconjugated hyperbilirubinemia may indicate a hemolytic problem (inherited possibly), or a non-hemolytic cause of increased bilirubin production, or a functional problem in bilirubin transport or metabolism in the liver (Gilbert's, Crigler-Najjar I or II). Any of these can be either benign or signs of a more serious problem. If the bilirubin in the baby is of the conjugated type, then the risk of the baby having a primary liver disease is significantly greater and could include such dignoses as biliary atresia, neonatal hepatitis and a wide range of inherited metabolic disorders. Most these diseases with conjugated hyperbilirubinemia are much more serious than the former group. Some of them may be inherited. Of course, the baby's jaundice may not be related at all to the disorder that the other members of the family have and a full diagnostic workup will be necessary to understand the cause of the jaundice. It must also be considered that the baby may,in fact, have been jaundiced from a much earlier time and that it was only noticed for the first time at five weeks. In that case, it is possible that it is a continuation of breastmilk jaundice, which has its onset in the first or second weeks of life, but may persist as long as three or four months, although with progressively declining serum bilirubin concentrations. Breastmilk jaundice is a benign condition, except for the very rare possibility of having a serum bilirubin level so high that it could cause kernicterus, but this theoretical more than demonstrated. In any event, stopping breastfeeding in a five week old is certainly not indicated and will do nothing to clarify the cause of the infant's jaundice. The infant needs a preliminary workup to determine what further studies are needed. Several recent review articles in the pediatric textbooks and journals (including my own in Pediatrics-In-Review November 1994) should help determine how to proceed diagnostically. Larry Gartner Lawrence M. Gartner, M.D. Professor of Pediatrics and Obstetrics/Gynecology The University of Chicago [log in to unmask] [log in to unmask]