Sensitivity of commercial prothrombin time reagents to detect coagulation factor deficiencies in equine plasma.
Authors: Mischke R, Junker J, Deegen E
Journal: Veterinary journal (London, England : 1997)
Summary
Commercial prothrombin time (PT) testing is widely used to assess equine coagulation status, yet the sensitivity of different reagents and protocols remains poorly characterised in equine medicine. Mischke and colleagues evaluated two commonly available PT reagents—human placental thromboplastin and recombinant human tissue factor—using both standard manufacturer protocols and modified procedures involving sample dilution and fibrinogen supplementation, testing them against dilution series of equine pooled plasma and 40 clinical samples with documented factor II, V, VII or X deficiencies. The recombinant tissue factor reagent used in standard testing demonstrated unacceptably poor sensitivity (0.20 overall, falling to 0.33 in clinically relevant samples with ≥20% factor reduction), whilst the placental thromboplastin reagent achieved adequate sensitivity (0.65 standard procedure; 0.60–0.75 modified procedure). Modified testing protocols with 1:20 sample dilution and fibrinogen addition improved sensitivity across both reagents but offered no clear advantage over placental thromboplastin in standard use. For equine practitioners, these findings underscore the critical importance of reagent selection when interpreting PT results; switching from recombinant to placental thromboplastin-based reagents would substantially improve the detection of clinically significant coagulation factor deficiencies without requiring protocol modification.
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Practical Takeaways
- •When performing PT testing on equine patients, reagent selection matters critically—human placental thromboplastin reagents provide better sensitivity than recombinant tissue factor for detecting coagulation defects
- •If your laboratory uses recombinant tissue factor reagent, consider implementing modified testing protocols (sample dilution with fibrinogen addition) to improve detection of clinically significant clotting factor deficiencies
- •Standard PT testing alone may miss mild-to-moderate coagulation disorders in horses; modified procedures increase diagnostic reliability when investigating bleeding disorders or pre-operative coagulation status
Key Findings
- •PT sensitivity with recombinant tissue factor reagent (0.20) was significantly lower than with human placental thromboplastin (0.65) in standard testing
- •Modified PT testing with sample dilution and fibrinogen addition achieved higher sensitivity (0.58-0.75) compared to standard procedures
- •For samples with ≥20% reduction in coagulation factor activity, recombinant reagent showed inadequate sensitivity (0.33) versus acceptable sensitivity (0.83-0.94) with other procedures
- •PT(MT) with 1:20 sample dilution demonstrated the highest sensitivity for detecting equine coagulation factor deficiencies