Ham Test
Synonyms Acid Serum Test; Acid Serum Test for PNH; Acidified Serum Test; Paroxysmal Nocturnal Hemoglobinuria Test; PNH Test; Serum Lysis
Laboratory Special Hematology
Request Form Routine Blood Requisition
Phone (212) 305-5001
Availability Mon-Fri, 8:30 AM - 1 PM
Turnaround Time Same day
Special Instructions Collection date and time must be on requisition. Specimen must be received by the laboratory within 2 hours after collection.
Specimen Blood
Volume 10 mL
Minimum Volume 7 mL
Container Two red top tubes or two gold top tubes
Collection Routine venipuncture
Causes for Rejection QNS, specimen hemolyzed, excessive delay in transport, does not meet labeling requirements
Reference Range A positive result shows lysis of patient's cells in acidified serum (not with normal cells) and with or without lysis in unacidified serum.
Use Evaluate patients with suspected PNH (paroxysmal nocturnal hemoglobinuria) or suspected congenital dyserythropoietic anemia, type II (HEMPAS); evaluate hemolytic anemia, especially with hemosiderinuria, pancytopenia, decreased RBC acetylcholinesterase, decreased leukocyte alkaline phosphatase, negative direct Coombs' test, and/or apparent marrow failure
Limitations False-positive results may occur in other hematologic diseases; hereditary and acquired spherocytosis, hereditary dyserythropoietic anemia (CDA type II, HEMPAS, vide infra), aged red cells (as with old transfused blood), aplastic anemia, leukemia, and myeloproliferative syndromes. In these conditions hemolysis will also occur in the acidified inactivated serum. The latter is negative in PNH since hemolysis is complement dependent.
Methodology Acidified serum test
Contraindications Recent transfusion
Additional Information PNH red cells are unusually susceptible to lysis by complement. The Ham (acidified serum) and sucrose hemolysis test can demonstrate this lysis in vitro. A positive acidified-serum test (performed with attention to proper controls) defines the PNH condition. A positive test is necessary for the diagnosis. In PNH 10% to 50% lysis (measured as liberated hemoglobin) is usually obtained but lysis may be as great as 80% or as little as 5%. Two populations of cells exist in patients with PNH. One is markedly sensitive to complement lysis, the other is only minimally susceptible to lysis. The young PNH cells (reticulocyte rich) are more susceptible to lysis than the older red cells. PNH RBCs will undergo lysis in acidified normal serum and in the patient's acidified serum.
The only other disorder which may give a positive Ham test is one of the congenital dyserythropoietic anemias. In CDA type II (HEMPAS - hereditary erythroblastic multinuclearity with positive acidified serum test) the red cells undergo lysis in only a proportion (approximately 30%) of normal sera and these RBCs do not undergo lysis in the patient's own acidified serum. The sucrose lysis test is negative in cases of HEMPAS.
Another type of cell that may lyse in inactivated serum is the spherocyte. Spherocytes may lyse in acidified serum possibly due to the lowered pH.
