From Vilas Hiremath, United Labs:
I have a patient with puberty menorrhagia. Her prothrombin time (PT) is prolonged, but corrected with normal pooled plasma (NPP). Her partial thromboplastin (PTT), thrombin time (TT), fibrinogen, FVII, and FV are all normal and her thromboelastography (TEG) R-value is prolonged to 60 minutes. Her factor X assay result is < 1%. We assessed the factor X activity using a PT-based assay. Since her factor X is deficient, why is her PTT normal?
Dear Vilas Hiremath, I took this to Dave McGlasson, Wilford Hall USAF Medical Center, who has done extensive research using all commercial PT and PTT reagents. Most PTT reagents are formulated to become prolonged in deficiencies of factors VIII, IX, and XI, but he found many are insensitive to low factor X activity levels. He expands by saying, however, that any PTT reagent should give a prolonged result when factor X is , 1%, so this may not really be the answer. He and I came up with the following suggestions:
- Try another PTT reagent: perhaps yours is just insensitive to factor X deficiency
- Try another factor X-deficient plasma reagent for your factor X assay, maybe you are encountering an effect related to factor VII
Sorry, we’ve not been very conclusive—let’s see what some of our participants suggest. Geo.