Diagnosis
Blood tests in PNH show changes consistent with intravascular hemolytic anemia: low hemoglobin, raised lactate dehydrogenase, raised reticulocytes (immature red cells released by the bone marrow to replace the destroyed cells), raised bilirubin (a breakdown product of hemoglobin), and decreased levels of haptoglobin. The direct antiglobulin test (DAT, or direct Coombs' test) is negative, as the hemolysis of PNH is not caused by antibodies.
Historically, the sucrose lysis test, in which a patient's red blood cells are placed in low-ionic-strength solution and observed for hemolysis, was used for screening. If this was positive, the Ham's acid hemolysis (after Dr Thomas Ham, who described the test in 1937) test was performed for confirmation.
Today, many labs use flow cytometry for CD55 and CD59 on white and red blood cells. Based on the levels of these cell proteins, erythrocytes may be classified as type I, II, or III PNH cells. Type I cells have normal levels of CD55 and CD59; type II have reduced levels; and type III have absent levels. The fluorescein-labeled proaerolysin (FLAER) test is being used more frequently to diagnose PNH. FLAER binds selectively to the glycophosphatidylinositol anchor and is more accurate in demonstrating a deficit than flow cytometry for CD59 or CD55.
Read more about this topic: Paroxysmal Nocturnal Hemoglobinuria