Ham’s Acid Lysis Test: Principle and Interpretation

Ham’s Acid Lysis Test is a test for the rare acquired red cell membrane disorder called paroxysmal nocturnal haemoglobinuria (PNH). Its pathophysiology is complex and involves an abnormality of the red cell membrane in PNH making it prone to complement-mediated lysis and episodes of marked intravascular haemolysis leading to free Hb in the urine (haemoglobinuria).

Principle

• Abnormal sensitivity of RBCs from patients with PNH to the haemolytic action of complement.
• Complement is activated by acidification of the patient’s serum to pH of 6.2, which induces lysis of PNH red cells, but not normal controls.

Sample: EDTA, heparin, citrate, oxalate.

Result: Positive result indicates PNH.

Specificity: High—similar reaction is produced only in the rare syndrome HEMPAS (a form of congenital dyserythropoietic anaemia type II), which should be easily distinguished morphologically. 

Sensitivity: Low—as the reaction is crucially dependent on the concentration of magnesium in the serum.