Features used to recognize in vitro hemolysis:
(1) visual discoloration of serum or plasma
(2) isolated abnormal chemical values in a specimen different from previous and/or repeat measurements
(3) history of improper collection, handling or transport
A visual color change to the serum or plasma becomes evident when the free hemoglobin level is > 3.1 µmol/L (> 200 mg/L, > 20 mg/dL; molecular weight of hemoglobin 64,500 daltons). In a patient with a hemoglobin of 15 g/dL the threshhold would represent hemolysis of 0.13% of the red cells (making several assumptions).
Blood chemistry values likely to be elevated with in vitro hemolysis:
(1) serum potassium
(2) LDH
(3) acid phosphatase
(4) AST and ALT, with AST > ALT
(5) total cholesterol (with severe hemolysis)
(6) free plasma hemoglobin
Confirmation of the diagnosis of in vitro hemolysis typically consists of repeating the tests with a specimen collected and handled to minimize in vitro hemolysis.
The differential diagnosis for in vitro hemolysis is in vivo hemolytic disease. In vivo hemolysis is likely when:
(1) A repeat specimen that is carefully collected shows the same findings.
(2) The patient has anemia and an increased total serum bilirubin (due to indirect bilirubin).
(3) The patient has a clinical diagnosis associated with in vivo hemolysis.
