Laboratory findings consistent with the diagnosis of paroxysmal nocturnal hemoglobinuria include low hemoglobin level, low RBCs count, and negative coombs test. Flow cytometry is the diagnostic test of choice where it shows GPI deficient RBCs.

Laboratory findings consistent with the diagnosis of PNH include:

• Due to hemolysis:
  1. Low hemoglobin
  2. Low RBC count
  3. Increased reticulocyte count
  4. Increased LDH
  5. Increased bilirubin
  6. Decreased haptoglobin
  7. Haemoglobinuria
  8. Negative coombs test

• Due to haemoglobinuria:
  1. Urinalysis: positive dipstick for heme with negative microscopic analysis for RBC
  2. Increased creatinine
  3. Increased BUN
  4. Iron deficiency: low iron, low ferritin, increased transferrin or TIBC

• Due to thrombosis:
  1. Thrombocytopenia
  2. Elevated liver function test

• Flow cytometry is the diagnostic study of choice to diagnose PNH. In PNH, flow cytometry shows decreased expression of GPI anchor on the RBCs surfaces.^[1]

• Other diagnostic studies not required for diagnosis include:
  • Bone marrow biopsy in cases of pancytopenia it may show hypocellular or normocellular marrow.