Acquired defects of hemostasis may first present with either prolongation of routine coagulation laboratory values or with a serious bleeding diathesis. Frequently DIC and liver disease present with both PT and aPTT elevated. If there is no evidence of either disorder then further testing is needed. A 50:50 mix that corrects establishes the presence of factor deficiency. One that does not correct (even with added phospholipids) suggests a specific factor inhibitor.
The first step in evaluation is to obtain a prothrombin time (PT) and an activated partial thromboplastin time (aPTT). One should ensure the sample is obtained from a peripheral vein. Samples drawn through heparin-locked catheters, even with elaborate manipulation to prevent contamination, can result in falsely elevated results as discussed in Chapter 2. Three patterns of defects can be seen
(Table 2.4). Isolated elevations of the PT are indicative of an isolated factor VII deficiency. Isolated elevations of the aPTT are typically due to heparin contamination, lupus inhibitors, isolated defects ofVIII, IX, XI, or the contact pathway. Mixing studies can provide information to narrow the list of possible diagnoses. Prolongation of both the PT and aPTT suggests multiple defects or deficiency of factors II, V, or X. Marked prolongation of the PT and aPTT can also be seen with low levels of fibrinogen (< 50 mg/dl).
Patients with hematocrits of greater than 60% may have spurious elevations of the PT and aPTT due to improper plasma:anticoagulant ratio in the sample tube. Further coagulation tests are ordered based on the PT and aPTT to define the defect better if the reason for the coagulation deficiency is not apparent by the history (i.e., severe liver disease).
Was this article helpful?