Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (919 page)

   Interpretation

   PTT, but not PT, is prolonged in severe deficiency.

   Asian populations have lower factor XII levels than Caucasians (average, 44%).

   Factor XII levels are decreased in the neonate; they reach adult values at 2 weeks of age.

   Factor XII levels are increased in pregnancy.

   Limitations

   Factor XII may be artifactually decreased by the presence of LA.

FACTOR XIII
*

   Definition

   Factor XIII is synthesized in the liver and also present in high concentrations in platelets. Factor XIII is a plasma transglutaminase proenzyme activated by thrombin in the presence of calcium. It promotes clot stability by forming intermolecular covalent bonds between fibrin monomers.

   
Normal range:
reported qualitatively as normal or decreased; quantitation performed in reference laboratories.

   Use

   Factor XIII values are decreased in factor XIII deficiency, which can be either inherited or acquired.

   Interpretation