Professional and Linguistic Assessments Board (PLAB) Practice Exam

What is the common indication of heparin toxicity?

1. High blood pressure

2. Prolonged aPTT

3. Elevated blood glucose

4. Low platelet count

The correct answer is: Prolonged aPTT

Heparin toxicity is primarily indicated by a prolonged activated partial thromboplastin time (aPTT). Heparin is an anticoagulant medication that works by inhibiting various factors in the coagulation cascade, particularly factors IIa (thrombin) and Xa. When the dosage of heparin is too high, it leads to excessive anticoagulation, resulting in a significant prolongation of the aPTT value. This is a crucial lab test used to monitor heparin therapy, and an increased aPTT indicates that the coagulation is being overly suppressed. The other options, while they might be relevant to different clinical scenarios, do not specifically indicate heparin toxicity. For instance, high blood pressure does not correlate with the mechanisms of heparin's action or toxicity. Elevated blood glucose levels could be related to stress responses or other metabolic conditions but are not a direct consequence of heparin use. Similarly, a low platelet count may be associated with heparin-induced thrombocytopenia (HIT), a rare but serious side effect, but it doesn't serve as a common indication of toxicity itself. Thus, the correct focus for identifying heparin toxicity is on the prolonged aPTT.