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Renal function was studied in 16 patients with cystic fibrosis, aged 5 to 19 years. The mean glomerular filtration rate and filtration fraction were increased compared to those in controls. Basal urinary sodium excretion as well as renal responses to oral and intravenous sodium loads were low, indicating an increased renal sodium reabsorption. Diluting capacity, measured as free water clearance, was decreased because of a low distal sodium delivery which might indicate an increased proximal sodium reabsorption.

To evaluate the variation in serum IgE levels during the neonatal period and its relation to the development of atopy, 83 infants with a heredity of atopy were studied with regard to the concentration of IgE in cord blood (CB) and capillary blood on the fourth or fifth day of life. During the neonatal period, the average IgE level remained unchanged in the whole group but there were large individual changes. Among 22 infants with CB-IgE levels greater than or equal to 0.9 kU/l the IgE concentrations in 50% decreased below this value on days 4-5. The correlation between maternal IgE and CB-IgE concentrations (rs = 0.41; P less than 0.001) was interpreted as indicating a probable contamination with maternal blood. This view was supported by the presence of an elevated IgA level and of IgE antibodies against inhalant allergens in 16% of the cord blood samples of which 69% had an IgE level exceeding 0.9 kU/l. It therefore seems preferable to collect the blood samples on the fourth or fifth day. However, in the 74 infants available for atopic classification at 18 months of age, the positive predictive value of IgE determinations was low: on days 4-5 25-38% and in CB 42%. A high CB-IgE level may merely be an indication of the mother's atopic state.

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