Paroxysmal nocturnal hemoglobinuria laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Laboratory Findings
A sugar or sucrose lysis test, in which a patient's red blood cells are placed in low ionic strength solution and observed for hemolysis, is used for screening. A more specific test for PNH, called Ham's acid hemolysis test, is performed if the sugar test is positive for hemolysis.[1] In a positive sucrose lysis test ionic strength facilitates the complement binding whereas in a positive Ham acid hemolysis test acidic strength facilitates the complement binding. The differential diagnosis of a positive sugar lysis test includes some autoimmune hemolytic anemias; even leukemias can give a false positive result. The differential diagnosis for a positive Ham test includes congenital dyserythropoietic anemia; note that a negative Ham test doesn't rule out PNH. These assays do not reliably quantitate the percentage of PNH cells and can be falsely negative in patients who have received red blood cell transfusions. Occasionally the characteristic complement-sensitive erythrocytes cannot be demonstrated in patients with well-established PNH. This probably occurs when the production of PNH cells is relatively low and most of the PNH cells that have been made have already been destroyed either in the marrow or in the circulation. Therefore a single normal sucrose hemolysis test cannot be considered absolute evidence that a patient does not have PNH.
References
- ↑ Ham TH. Chronic haemolytic anaemia with paroxysmal nocturnal haemoglobinuria: study of the mechanism of haemolysis in relation to acid-base equilibrium. N Engl J Med 1937;217:915-918.