Unexpectedly High PTT Values After Low-Dose Heparin Prophylaxis

T hromboembolic (TE) prophylaxis using lowdose unfractionated heparin (LD-UFH), ie, 5000 IU given subcutaneously twice or 3 times daily is effective, has low bleeding risk, and is generally not expected to prolong partial thromboplastin times (PTTs). Laboratory monitoring or dose adjustments based on weight or renal function are not considered necessary. An index case at our institution prompted us to review this conventional view and investigate the frequency and circumstances when significant PTT prolongations occur in hospitalized patients receiving LD-UFH for TE prophylaxis.