If the PT or PTT/aPTT is abnormal, but the nature of the factor deficiency is unknown, specific coagulation factors may be measured. Factor assays require specialized techniques not available in many laboratories. Factor assays are used to discriminate among mild, moderate, and severe deficiencies and to follow the course of acquired factor inhibitors. States associated with particular factor deficiencies are presented in Table 2-7.

Factors of the extrinsic (II, V, VII, X) and intrinsic (VIII, IX, XI, XII) coagulation pathways are usually measured separately. The factor XIII assay is a separate test in which a blood clot is observed for 24 hours. Clot dissolution within this time indicates severe factor XIII deficiency. The test for fibrinogen (factor I) is discussed later.

Note: Normal values vary among laboratories.

• Therapy with anticoagulants and other drugs known to alter hemostasis
• Traumatic venipunctures and excessive agitation of the sample may alter test results

• Prolonged PT or PTT of unknown etiology:
  • If the PT is prolonged but the PTT is normal, factors of the extrinsic pathway are evaluated (i.e., factors, II, V, VII, and X).
  • If the PTT is prolonged but the PT is normal, factors of the intrinsic pathway are evaluated (i.e., factors VIII, IX, XI, XII).
• Monitoring of effects of disorders and drugs known to lead to deficiencies in clotting factors (see Table 2-7, p. 55)

Nursing Care Before the Procedure

Client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

• If the individual is receiving anticoagulant therapy, the time and the amount of the last dose should be noted.

For assays of the factors involved in the intrinsic and extrinsic coagulation pathways, a venipuncture is performed and the sample collected in a light-blue-topped tube. For factor XIII assays, the sample is collected in a red-topped tube. As with other coagulation studies, traumatic venipunctures and excessive agitation of the sample should be avoided. The samples should be sent to the laboratory immediately.

Nursing Care After the Procedure

Care and assessment after the procedure are essentially the same as for any study involving the collection of a peripheral blood sample.

• Because the client may have a coagulation deficiency, maintain digital pressure directly on the puncture site for 3 to 5 minutes after the needle is withdrawn.
• Inspect the site for excessive bruising after the procedure.