[Does febrile proteinuria exist?]

The significance of proteinuria during febrile infectious diseases is widely underestimated, although the more marked proteinuria probably signalizes a parainfectious nephropathy rather than a functional disorder. This study shows that mild proteinuria of less than 0.65 g/24 h (normal range less than 0.3 g/24 h using the sensitive tannine-FeCl3-technique) might be caused by the elevated body temperature alone. 9 out of 18 volunteers without renal disease undergoing experimental hyperthermia of 40-41 degrees C for 1-2 h did not develop a proteinuria according to quantitative and qualitative (SDS-PAGE) measurements. In 6/18 the amount and composition of urinary proteins changed giving a glomerular type of proteinuria, possibly caused by temperature related transient glomerular alterations. In 3/18 a mild glomerulopathy existed before hyperthermia, as deduced from a glomerular pattern despite a quantitatively physiological proteinuria, leading in all 3 to pathological proteinuria during hyperthermia. In all 18 volunteers alterations reversed to normal within 12 h. Therefore, the degree of proteinuria during febrile diseases should be considered. Proteinuria of less than 0.5-1 g/24 h in adults might be explained by an altered glomerular function alone. Proteinurias exceeding this value, with a slow regressing tendency will indicate glomerular or tubulo-interstitial diseases, caused possibly by immunologic or toxic products resulting from underlying infectious disease.