HEMOGLOBINURIA

Abstract

The author critically surveys the exptl. findings relating to hemoglobinuria in an effort to reconcile the escape of large molecules through the normal kidney with the modern filtration theory of renal function. He does not inquire into the causes of hemoglobinemia. The sifted evidence makes the following conclusions seem probable though final proof is lacking. Hb escapes by filtration through the glomerulus rather than by excretion through the tubular epithelium. The glomerular membrane is not damaged by the Hb to make it permeable but presents pores of graded sizes,[long dash]the few large ones accommodating the Hb molecule. The effective size of a pore depends both on its spatial dimensions and also on electro-chemical charges on membrane and Hb particle. The renal threshold is detd. for Hb, as for many other substances, by tubule reabsorption. The rate at which the tubules absorb depends on the amt. they have previously absorbed and the speed with which they dispose of it. When the urine is alkaline the renal threshold in man is about 135 mg. of Hb per 100 cc. plasma, in the dog from about 80 to 150 mg. The fraction of injected Hb which is recovered in urine is proportional to the dose above the level of 100-150 mg. per kg; it reaches as high as 35-40%. When the urine is acid considerable amts. of Hb precipltate in the lumina of the tubules. These casts do not seem responsible per se for the renal failure that is sometimes coincident with them, though they probably contribute.