Factors potentially affecting or influencing PT may include the following:
- Shortening of PT
- Physiological
- Pregnancy
- Aging
- Exercise
- Pathological
- VTE & ATE
- Malignancy
- Sepsis
- Thyroid disorders
- Therapeutic
- rFVIIa
- Estrogen medications
- Spurious
- Prolonged venous stasis of >3 mins
- Coagulation before centrifugation
- Hyperbilirubinemia
- Hypertriglyceridemia
- Hemolyzed sample
- Excess vigorous mixing of blood
- Chilling in refrigerator or placing on ice
- Incomplete Platelet separation
- Sample re-run after freezing
- Tube leaded into long track/belt in completely automated system
- Analytical error
- Prolongation of PT
- Physiological
- None
- Pathological
- Vitamin K deficiency
- Liver Disease
- FI, FII, FVII, FV, FX deficiency
- Afibrinogenemia
- Dysfibrinogenemia
- DIC
- Lupus anticoagulant
- Therapeutic
- Warfarin & other VKAs
- Direct FIIa inhibitors
- Oral → Dabigatran
- Parenteral
- Hirudin
- Bivalirudin
- Argatroban
- Anti-FXa drugs
- Heparin, Heparinoids, LMWH, Pentasaccharides
- Spurious
- Heparin contamination
- Clotted sample
- EDTA contamination (calcium chelation)
- Under filled tube (<90% of the nominal volume)
- Failure to mix specimen after collection
- Sample held too long before analysis
- Sample placed on wrong temperature
- Use of centrifuge brake
- Analytical error
- Unfractionated Heparin
- Most reagents are less sensitive to UFH due to
- Nature of PT assay
- Inclusion of Heparin Neutralizing agent in most PT reagents
- PT reagent is sensitive when concentrated Heparin contaminates the sample
- LMWH
- PT reagents are even less sensitive to LMWH than WFH
- Heparinoids (anti-FXa activity)
- PT reagents are even less sensitive to Heparinoids than WFH
- Pentasaccharides (Fondaparinux)
- PT reagents are even less sensitive to Fondaparinux than WFH
- Clotted Sample
- Serum or fully Clotted sample → No fibrinogen → No clot in PT, APTT or TT
- Partially clotted sample → Falsely Prolonged PT, APTT & TT or Shortened APTT
- Hemolyzed sample
- Hemolyzed RBCs → Phospholipid membranes → Coagulation accelerated → Shortened PT
- Hemolyzed RBCs → Platelet activation → Impaired PT results
- Change in the color of plasma & particulate material → interferes with optical end-point detection methods
- Over & underfilled sample tube
- Lupus anticoagulant
- Most PT reagents are insensitive to LA
- Some PT reagents are sensitive to LA
- Daptomycin therapy
- Spuriously prolongs the PT
- Depends upon 2 factors
- Thromboplastin source
- Especially prolonged PT when recombinant human or rabbit thromboplastins are used
- Phospholipid type of the PT reagent
- Prolongation occurs mostly when Phosphatidylglycerol is used as phospholipid in PT reagent
- Vigorous shaking mixing of blood sample
- Hemolysis & platelet activation → activation of coagulation cascade → PT falsely shortened
- Chilling in refrigerator (≤40C) or placing the plasma on ice
- Activation of FVII activation of coagulation cascade → PT falsely shortened
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