The best screening tests for disorders of coagulation are a history and physical examination. Coagulation screening, a useful combination of laboratory tests, consists of a prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen and platelet count. The screening coagulation tests are designed to provide rapid, useful, non-specific information, which allows an initial broad categorization of the hemostatic problem. The results of these screening tests, in conjunction with the clinical history, will then direct the selection of further, more detailed and specific coagulation tests, such as specific factor assays, fibrin degradation products, D-dimer, thrombin time, platelet aggregation, or specific factor inhibitor assays.
Based on the results of the PT and APTT, a disorder of hemostasis can be broadly categorized as shown in Table I.
Protime |
APTT |
Possible Abnormality |
Normal |
Normal |
Qualitative or Quantitative Platelet Defect
Vascular Defect
Factor XIII Deficiency
Alpha-2 Antiplasmin Deficiency |
Increased |
Normal |
Hereditary Factor VII Deficiency
Warfarin therapy
Early Vitamin K deficiency
Early liver dysfunction |
Normal |
Increased |
Hemophilia A
Hemophilia B
von Willebrand's Disease
Factor XI deficiency
Factor XII deficiency (no bleeding history)
HMWK deficiency (no bleeding history)
Prekallikrein deficiency (no bleeding history)
Coagulation inhibitor
Heparin |
Increased |
Increased |
Factor X deficiency
Factor V deficiency
Factor II deficiency
Hypofibrinogenemia/Dysfibrinogenemia
Liver disease
Vitamin K deficiency
DIC
Warfarin therapy
Heparin |
Reference ranges are:
Test |
Reference Range |
Critical Value |
Prothrombin Time |
11.4 - 14.2 sec |
>17 sec
>25 sec if anticoagulated |
APTT |
22 - 32 sec |
>45 sec
>130 sec if heparinized |
Platelet count |
140,000 - 400,000/uL |
<30,000/uL
>1 million/uL |
Fibrinogen |
146 - 390 mg/dL |
<100 mg/dL |
Specimen requirement is one light blue top (sodium citrate) tube and one lavender top (EDTA) tube of blood.
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