Circulating Inhibitor in an Elderly Female That Impairs the Action of Human But Not Rabbit Brain Thromboplastin

Abstract number: P1911

Messmore^1,2 HL, Adess^1,2 M, Fabbrini² N, Choudhury^1,2 A, Bhoopalam^1,2 N, Diaz¹ M, Iqbal¹ A, Balbale² S, Love² B, Zarr² C, Schlimm² S, Bird² ML

^{1,2 1,2 11}Loyola University Stritch School of Medicine, Maywood, Illinois, USA ²²Hines VA Hospital, Hines, Illinois, USA

A 71 year old female with dementia (ischemic strokes in the past), no history of overt bleeding, a history of abnormal coagulation tests for over 10 years, iron deficiency anemia (on oral aspirin chronically), diabetes mellitus (adult onset), and no other significant problems was found to have a markedly prolonged prothrombin time (PT) with a normal activated partial thromboplastin time (APTT). Coagulation testing revealed the following results:

PT: 110 seconds, 80.3 seconds, 77.1 seconds (Ref Range 9.0–11.8 seconds)

APTT: 29.5 seconds, 29 seconds, 29 seconds (Ref Range 22–34 seconds)

Thrombin Time: 17.9 seconds (Ref Range 12–21 seconds)

Fibrinogen: 598 mg/dL (Ref Range 200–400 mg/dL)

Inhibitor Screen: Positive (Immediate Acting)

Lupus Anticoagulant Screening Profile: Negative

Factor Assays V, VII, VIII, IX, X, II were all normal

ANA, anti-DS DNA, Immunoglobulin Assays and Blood Viscosity were normal

Additional studies revealed a prothrombin time with rabbit brain thromboplastin (Dade^® Thromboplastin C Plus^®) of 13.2 seconds as compared with a prothrombin time of 79.4 seconds with recombinant human tissue factor thromboplastin (Dade^® Innovin^®).

The patient's serum was inhibitory to Innovin^® but not to Thromboplastin C Plus^® as determined by mixing her serum 1 : 1 with normal human plasma. The inhibition was immediate. Recombinant Factor VIIa (NovoSeven^®) added to her plasma partially corrected the abnormal prothrombin time when supplemented at therapeutic concentrations in vitro.

Conclusion:  Inhibitor of human tissue factor by both patient serum and plasma.