The partial thromboplastin time (PTT) test is used to evaluate the intrinsic and common pathways of the coagulation sequence. It represents the time required for a firm fibrin clot to form after phospholipid reagents similar to thromboplastin reagent are added to the specimen. Because coagulation factor VII is not required for the PTT, the test bypasses the extrinsic pathway (see Fig. 2-1).

To give a normal PTT result, factors XII, XI, IX, VIII, X, V, II (prothrombin), and I (fibrinogen) must be present in the plasma. The PTT is more sensitive than the PT in detecting minor deficiencies of clotting factors because factor levels below 30 percent of normal prolong the PTT.

The activated partial thromboplastin time (aPTT) is essentially the same as the PTT but is faster and more reliably reproducible. In this test, the thromboplastin reagent may be kaolin, celite, or ellagic acid, all of which more rapidly activate factor XII.

It is possible to infer which factors are deficient by comparing the results of the PTT with those of the PT. A prolonged PTT with a normal PT points to a deficiency of factors XII, XI, IX, and VIII and to von Willebrand's disease. In contrast, a normal PTT with a prolonged PT occurs only in factor VII deficiency.³²

In addition to heparin therapy and coagulation factor deficiencies, the following also prolong the PTT: circulating products of fibrin and fibrinogen degradation, polycythemia, severe liver disease, vitamin K deficiency, DIC, and established therapy with coumarin anticoagulants.

* Values can vary among laboratories.

• Heparin and established therapy with coumarin derivatives alter the PTT.
• Traumatic venipunctures may lead to erroneous results because of activation of the coagulation sequence.
• Excessive agitation of the sample may prolong the PTT.

• Signs of abnormal bleeding such as epistaxis, easy bruising, bleeding gums, hematuria, and menorrhagia
• Identification of individuals who may be prone to bleeding during surgical, obstetric, dental, or invasive diagnostic procedures
• Evaluation of responses to anticoagulant therapy with heparin or established therapy, or both, with coumarin derivatives and determination of dosage required to achieve therapeutic results
• Detection of congenital deficiencies in clotting factors such as hemophilia A (factor VIII) and hemophilia B (factor IX), which alter the PTT
• Monitoring of effects on hemostasis of conditions such as liver disease, protein deficiency, and fat malabsorption

Nursing Care Before the Procedure

In general, 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.

A venipuncture is performed and the sample collected in a light-blue-topped tube. Traumatic venipunctures and excessive agitation of the sample should be avoided.

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.
  • Bleeding episode: Report increase in PTT or aPTT during heparin therapy; note that a therapeutic range is maintained (usually 1.5 to 2.5 times the control). Note also (1) drugs taken that can interfere with the action of heparin therapy, (2) the administration of prophylactic low-dose heparin that does not require PTT testing, and (3) symptoms such as bleeding from any area (blood in sputum, urine, feces; bleeding from nose, skin, mucous membranes). Adjust dosage according to physician order. Protect from trauma to skin, mucous membranes, organs, and joints (falls; rough handling of extremities; shaving; brushing teeth; IM, SC, and IV injections; suctioning). Test for occult blood in body secretions and excretions. Inform client to avoid drugs that affect the PTT. Provide special considerations to allay anxiety related to possible bleeding tendencies.
  • Critical values: Notify the physician at once of an increase of greater than 20 seconds above the control if the individual is not receiving heparin therapy. If heparin therapy is administered, a PTT level of less than 53 seconds indicates an inadequate anticoagulation effect; the physician should be told immediately if a level is greater than 2.5 times the control time level.