Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (241 page)

   Fava bean sensitivity, G6PD deficiency, and other hemoglobinopathies

   Severe hereditary spherocytosis

   Other hematologic crises (e.g., disseminated intravascular coagulation [DIC], incompatible transfusion reactions).

   Infections (e.g.,
Clostridium perfringens
[previously known as
Clostridium welchii
];
E. coli
bacteremia from transfused blood;
Bartonella bacilliformis
, the agent of Oroya fever or Carrion disease).

   Parasitemias (e.g., malaria).

   Organ damage (e.g., kidney infarction, diabetic acidosis).

   Physical or chemical trauma (e.g., strenuous exercise, march hemoglobinuria, thermal burns, infusion or bladder irrigation with hypotonic solutions, naphthalene, sulfa drugs).

   Laboratory Findings

   The diagnosis of intravascular hemolysis is usually based on the medical history and analysis of blood and urine specimens. A positive dipstick test and the microscopic absence of urine RBCs and RBC casts suggest hemoglobinuria or myoglobinuria.

   Serum LDH and haptoglobin: The combination of an increased level of serum LDH and a reduced level of haptoglobin has been shown to be 90% specific for the diagnosis of hemolysis, whereas the combination of a normal serum LDH and a serum haptoglobin >25 mg/dL has been shown to be 92% sensitive for ruling out hemolysis.

   Free Hb: In correlation with hemosiderin in the urine sediment, the finding of free Hb in the plasma and/or urine is highly specific for the presence of intravascular hemolysis.

   Spectrophotometry: Presence of Hb in both urine and plasma (deoxy Hb highest absorption peak is at 420 nm, with a secondary peak at 580 nm) is indicative of intravascular hemolysis.

   Serum conjugated bilirubin and urine urobilinogen: Both are elevated with hemolysis.