RENAL FUNCTIONAL RESERVE IN CHILDREN WITH A PREVIOUS EPISODE OF HEMOLYTIC-UREMIC SYNDROME

Renal function [creatinine clearance (C(Cr)] and renal functional reserve (RFR) was measured in 16 children who had had haemolytic-uraemic syndrome (HUS) an average of 6.6 +/- 0.72 years previously. All patients had normal plasma creatinine and blood pressure and only 3 had proteinuria, which was mild in every instance. Patients were studied whilst ingesting three diets which provided an average of 1.5, 2.1 and 3.1 g protein/kg body weight per day, respectively. Diets were administered over three consecutive periods of 7 days each and C(Cr) was measured on the 7th day of each diet. Values tended to correlate with protein intake. They were in the normal range when patients were taking 1.5 and 2.1 g protein diets and increased markedly in 13 of the 16 patients (P < 0.001) when they ingested the high-protein diet (3.1 g). The effect on glomerular filtration rate (GFR) - measured by C(Cr) and inulin clearance (C(in) - of an acute oral protein load was studied in 12 of the HUS patients and four control subjects. In the control periods, prior to the protein load, values for C(Cr) were similar in the HUS and control subjects (104.0 +/- 11.0 vs 121.6 +/- 10.1 ml/min per 1.73 m2, NS). However C(in) values were significantly reduced in HUS patients (59.5 +/- 9.2 vs 102.7 +/- 12.4 ml/min per 1.73 m2, (P < 0.025). The C(Cr)/C(in) ratio in the patients averaged 2.10 compared with 1.13 in controls. Acute protein loading was accompanied by an increase in C(in) in all controls but in only 8 of the 12 patients. Baseline values for C(in) did not correlate with the presence or absence of protein-stimulated enhancement of C(in). The C(Cr)/C(in) ratios after protein loading remained twice as high in HUS patients as in controls. The data indicate that C(Cr) is not an accurate indicator of GFR in children who have had acute renal injury. Tubular secretion of creatinine represents a greater proportion of excreted creatinine in these children, may maintain serum creatinine in the normal range and mask the decrease in GFR. The study also emphasizes the problems of measuring RFR in these children.