Urinary potassium excretion in newborns with and without icterus neonatorum.

The precise mechanism underlying the common 'physiological' jaundice of the newborn remains uncertain (Goldbloom and Gottlieb, 1929; Billing and Lathe, 1956; Lathe and Walker, 1957; Nelson, 1964). This study was based upon a previous suggestion that increased haemolytic activity operates in some cases, and that an increased urinary potassium concentration is one expression of this, continuing as long as abnormal haemolytic activity persists (Gotlieb and Pesach, 1962). In an earlier investigation of newborn infants affected by icterus neonatorum (Gotlieb, Pesach, and Rimon, 1961), 16 out of 18 showed the presence of lysolecithin in serum after incubation with lecithin. Under the same conditions lysolecithin was shown in only 1 of 10 infants without icterus neonatorum. Further studies (unpublished) showed that the difference in serum lysolecithin concentrations between the two groups of newborns was smaller than previously reported, though still statistically significant. Lysolecithin, which is known to be a strong haemolytic agent, may thus be a causative factor in icterus neonatorum. More direct evidence is needed, however, to substantiate haemolytic theories of idiopathic icterus neonatorum. Since erythrocytes have a high content of potassium (420 mg./100 ml. RBC, Wintrobe, 1961), and since the renal excretion of potassium in the newborn is apparently efficient (McCance and Widdowson, 1954; Tudvad, McNamara, and Barnett, 1954), a rise in urinary potassium concentration may serve as an index of haemolysis (Gotlieb and Pesach, 1962). The present investigation was designed to reappraise the significance of differences between potassium excretion in newborns with and without physiological jaundice.