A woman with glucose-6-phosphate dehydrogenase (G6PD) deficiency develops a urinary tract infection. Free radicals generated by responding neutrophils create an oxidant stress, and RBCs are rapidly overwhelmed. As soon as intravascular hemolysis begins, serum levels of which of the following will decrease?
Correct Answer: Haptoglobin
Description: Haptoglobin (or alpha-2 globulin) is a serum protein that promptly binds to free hemoglobin in the serum, forming a tight complex. The haptoglobin-hemoglobin complex is quickly cleared from the blood by the reticuloendothelial system, which allows the hemoglobin to be salvaged instead of lost into the urine. Intravascular hemolysis from any cause is rapidly followed by a dramatic drop in serum haptoglobin. Bilirubin is synthesized in the liver and spleen as an end-product of heme degradation. Serum bilirubin levels would not change until the haptoglobin in the blood was completely saturated, and free hemoglobin began to circulate. In this circumstance, serum bilirubin would increase, not decrease. C-reactive protein an acute phase reactant produced by the liver in increased quantity in response to inflammation. This patient's urinary tract infection would increase C-reactive protein levels, but the hemolysis would not fuher affect them. Serum free iron does not change appreciably in intravascular hemolysis. Ferrous iron in the red blood cell is complexed to hemoglobin, and this complex is not broken in hemolysis. Ref: Beutler E. (2010). Chapter 42. Disorders of Iron Metabolism. In J.T. Prchal, K. Kaushansky, M.A. Lichtman, T.J. Kipps, U. Seligsohn (Eds), Williams Hematology, 8e.
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