Overview
Ham’s test, also known as the acidified serum lysis test, is a laboratory test used in the diagnosis of paroxysmal nocturnal hemoglobinuria. It is based on the principle that red blood cells with membrane defects undergo complement-mediated lysis when incubated in acidified serum. Acidification activates the alternative complement pathway, leading to selective hemolysis of abnormal cells. Ham’s test was historically considered a standard diagnostic method for PNH and is more specific than the sucrose lysis test, though it has largely been replaced by flow cytometry in current practice.
Symptoms
Patients evaluated with Ham’s test usually present with symptoms related to chronic intravascular hemolysis. Common features include dark-colored urine, especially in the morning, fatigue, pallor, shortness of breath, dizziness, headache, abdominal pain, and back pain. Recurrent infections, gallstones, and an increased tendency for venous thrombosis may also be seen. Symptoms may be intermittent and vary in severity depending on the extent of red cell destruction.
Causes
A positive Ham’s test occurs due to increased sensitivity of red blood cells to complement-mediated lysis in acidified serum. This is most commonly seen in paroxysmal nocturnal hemoglobinuria, where red cells lack protective complement regulatory proteins. Similar hemolysis may rarely be observed in congenital dyserythropoietic anemia type II and in HEMPAS. Acidification of serum to a specific pH is essential, as it activates the complement pathway responsible for red cell lysis.
Risk Factors
Risk factors associated with conditions detected by Ham’s test include underlying bone marrow disorders, aplastic anemia, unexplained Coombs-negative hemolytic anemia, and recurrent thrombotic episodes. Recent blood transfusions, improper sample handling, and complement inactivation can affect test accuracy. Patients with longstanding anemia, hemoglobinuria, or thrombosis without an obvious cause are more likely to require evaluation.
Prevention
There is no specific prevention for disorders identified by Ham’s test, but early diagnosis helps reduce complications such as severe hemolysis and thrombosis. Proper sample collection, timely testing with fresh complement, and strict adherence to procedural steps improve reliability. Although flow cytometry has replaced Ham’s test for definitive diagnosis, early recognition and appropriate clinical management of PNH significantly improve patient outcomes.
