A 56-year-old man is being evaluated for increased fatigability. His past medical history is significant for severe aortic stenosis that required aortic valve replacement, diabetes mellitus, and osteoarthritis. Peripheral blood smear findings are shown on the slide below. Which of the following laboratory findings is most likely to be seen in this patient?

Question

A 56-year-old man is being evaluated for increased fatigability.  His past medical history is significant for severe aortic stenosis that required aortic valve replacement, diabetes mellitus, and osteoarthritis.  Peripheral blood smear findings are shown on the slide below.  Which of the following laboratory findings is most likely to be seen in this patient?

Quizplus · Accepted Answer

The fragmented erythrocytes shown on the slide are called schistocytes or helmet cells. They are formed during mechanical destruction of erythrocytes in the vasculature. In this patient, destruction of erythrocytes is most likely to be caused by his aortic valve prosthesis. Artificial (mechanical) valves are more traumatic for red blood cells (RBCs) than porcine prostheses and frequently cause hemolysis. Schistocytes also appear if erythrocyte destruction occurs due to narrowing of vascular spaces or disseminated thrombosis. Hemolytic anemia due to intravascular erythrocyte trauma results in laboratory findings similar to other types of hemolytic anemias such as an increase in serum indirect bilirubin and urinary urobilinogen. Intravascular erythrocyte destruction results in free hemoglobin in the serum (hemoglobinemia) and in the urine (hemoglobinuria) as well as increased serum lactate dehydrogenase. Haptoglobin is a serum protein that binds free hemoglobin and promotes its excretion by the reticuloendothelial system. In intravascular hemolysis, the amount of free hemoglobin in the serum exceeds the binding capacity of haptoglobin, thereby decreasing the level of haptoglobin (Choice B). (Choice A) Increased serum iron occurs in hemochromatosis most classically, but increased serum iron can also be iatrogenic. Hemochromatosis does not cause anemia, but it is associated with cirrhosis, and increased incidence of hepatocellular cancer, skin darkening and insulin resistance. (Choice C) Most cases of hemolytic anemia are accompanied by an increased mean corpuscular volume (MCV) as intensive erythropoiesis causes the appearance in peripheral blood of premature erythroid forms larger than normal erythrocytes. Less commonly, the MCV can be normal or decreased (eg, due to the presence of smaller spherocytes or due to chronic anemia causing iron deficiency). Decreased haptoglobin is more specific for hemolysis and more likely to be seen in this patient. (Choice D) A decreased reticulocyte count in the presence of anemia is characteristic of aplastic anemia. In hemolytic anemias, the reticulocyte count is increased in order to compensate for the increased destruction of RBCs. (Choice E) A decreased serum albumin level is associated with cirrhosis (decreased production), nephrotic syndrome and protein-wasting enteropathy (increased losses). Educational objective: Schistocytes (helmet cells) are fragmented erythrocytes. They occur in microangiopathic hemolytic anemias (eg, disseminated intravascular coagulation, hemolytic-uremic syndrome, thrombotic thrombocytopenic purpura) and due to erythrocyte destruction by prosthetic cardiac valves. Hemolytic anemias are characterized by a decreased serum haptoglobin level as well as an increased lactate dehydrogenase and bilirubin.

A 56-Year-Old Man Is Being Evaluated for Increased Fatigability