Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (970 page)

   Multiple identified and unidentified metabolites formed, resulting in a low confirmation rate for LSD of positive-screened specimens

HAPTOGLOBIN

   Definition

   Haptoglobin is a glycoprotein synthesized mainly in the liver. It sequesters free Hb released from hemolyzed RBCs, which is transported by macro-phages to the liver where the heme is broken down to bilirubin. The same function is served by hemopexin and especially albumin. Haptoglobin is also an acute-phase reactant.

   
Normal range:
36–195 mg/dL.

   Use

   Most sensitive test for RBC destruction; absent when the rate of destruction is double that of normal

   Indicator of chronic hemolysis (e.g., hereditary spherocytosis, PK deficiency, sickle cell disease, thalassemia major, untreated PA).

   In the diagnosis of transfusion reaction by comparison of concentrations in pretransfusion and posttransfusion samples. In a posttransfusion reaction, the serum haptoglobin level decreases in 6–8 hours; at 24 hours, it is <40 mg/ dL or <40% of pretransfusion level.

   In paternity studies, may aid by determination of haptoglobin phenotypes.

   Evaluate known or suspected disorders involving a diffuse inflammatory process or tissue destruction, as indicated by elevated levels.

   Interpretation

Increased In

   Conditions associated with increased ESR and α-2 globulin (infections, inflammation, trauma, necrosis of tissue, hepatitis, scurvy, amyloidosis, nephrotic syndrome, disseminated neoplasms such as lymphomas and leukemias, collagen diseases such as rheumatic fever, RA, and dermatomyositis). Therefore, these conditions may mask the presence of concomitant hemolysis.

   One third of patients with obstructive biliary disease.