Hematology Laboratory Discussion

Summary:

This Hematology Laboratory Discussion note describes a clot-based test that is performed on blood plasma to distinguish factor deficiencies from factor inhibitors. The test involves combining one part normal plasma and one part patient plasma and then testing by partial thromboplastin time (PTT) immediately or after an incubation period. Correction with mixing indicates factor deficiency, while failure to correct indicates an inhibitor. The note also describes the different coagulation factor groups, their properties, and how to identify the pathway by looking at the results of PT and APTT. Intrinsic, extrinsic, and common pathways are discussed, and the note provides examples of factor deficiencies for each pathway. The note concludes with a reference list and a table that summarizes the results of the mixing study.

Excerpt:

Hematology Laboratory Discussion

• A clot-based test in which 1 part normal plasma and 1 part patient plasma are combined and then tested by the partial thromboplastin time (PTT) immediately or after an incubation period. A factor deficiency of the patient will show a correction to a normal PPT for the mix. An inhibitor in the patient’s plasma will not correct to a normal PTT with the mix
• Tests performed on blood plasma are used to distinguish factor deficiencies from factor inhibitors
  • Example: Lupus anticoagulant or specific factor inhibitors such as antibodies directed against Factor VIII
• Used to identify specific factor deficiency by mixing correction reagents with the patient’s plasma and then performing PT and APTT
• Distinguish clotting time prolongation due to a coagulation factor deficiency or an inhibitor
• Mix patient plasma and normal pooled plasma and measure the clotting time that was initially
  prolonged
• The patient plasma is mixed 1:1 with normal pooled plasma that contains 100% of the normal factor level, resulting in a level of 50% in the mixture
• Correction with mixing indicates factor deficiency, failure to correct an inhibitor