A short survey is given of the literature on haptoglobin, the hemoglobin-binding serum protein, its properties and biologic variations. The principles of an electrophoretic method for quantitative determination of the serum haptoglobin are described.

Electrophoretic studies showed that haptoglobin has a high affinity for hemoglobin at physiologic pH and that every haptoglobin molecule can bind at least 2 hemoglobin molecules.

Observations made following the intravenous injection of hemoglobin showed:

that hemoglobin administered intravenously is bound by the haptoglobin;

that free hemoglobin is not demonstrable until more hemoglobin has been injected than can be bound by the haptoglobin;

that the complex hemoglobin-haptoglobin is eliminated from the plasma after intravascular hemolysis or intravenous administration of hemoglobin without being excreted in the urine;

that the hemoglobin-haptoglobin complex is removed from the plasma at a constant rate during the major part of the elimination period;

that the haptoglobin level will fall to nil within 24 hours, if the amount of hemoglobin injected is sufficient to bind all the haptoglobin available. During the following days the rate of formation of haptoglobin can be studied.

From the data available it can be concluded that hemoglobinuria cannot appear until the amount of hemoglobin administered intravenously or the amount liberated intravascularly exceeds the binding power of the haptoglobin and the reabsorption capacity of the tubules. The variation observed by earlier authors in the so-called renal threshold for hemoglobin on intravenous injection of hemoglobin can be explained among other things by the variation in the haptoglobin content in one and the same subject, i.e., if the haptoglobin level is low, the threshold value will also be low, and vice versa.

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