Prothrombin Time(PT)

Prothrombin Time(PT)

Normal range

      11 –16 seconds

      Indication

Control of long – term oral anticoagulant therapy with coumarins and indanedione derivatives; evaluation of liver functions( PT is the most useful test of impaired liver synthesis of prothrombin complex factors[ factor II, VII, IX, Protein C & S]; evaluation of coagulation disorders- screen for abnormality of factors involved in extrinsic pathway (factor V, VII, IX, Prothrombin, fibrinogen). Should be used with a PTT.

Prolonged by defect in

Factor I, II, V, VII and X

Prolonged in

In adequate vitamin K in diet, premature infants, newborns of vitamin K deficient mothers, poor fat absorption (obstructive jaundice, colitis, steatorrhea), severe liver damage (hepatitis, poisoning), anticoagulant drugs, familial hypoprothrombinemia. 

Coagulation Time/ Clotting Time (CT)

Coagulation Time/ Clotting Time (CT)

Normal range

 6 –17 minutes (glass tube),

Indications and Interpretations         

Former routine method for control of heparin therapy but now replaced by a partial thromboplastin time(PTT) as it is not a reliable screening test for bleeding conditions because it is not sensitive enough to detect mild conditions but only detects severe ones; normal coagulation time does not rule out a coagulation defect; routine preoperative bleeding and coagulation time are of  little value for preoperative screening.

Prolonged in

Severe deficiency (< 6%) or any known plasma clotting factors except factor XII and factor VII, afibrinogenemia and presence of circulating anticoagulant (including heparin).

Normal in

Thrombocytopenia, deficiency of factor VII, von Willebrand's disease, and mild coagulation defects due to any causes.

Bleeding Time (BT)

Bleeding Time (BT)

 

Normal Range

3 – 9.5 minutes

Indications and Interpretations         

·        BT is functional test of primary hemostasis

·        BT is single screening test for platelet functional or structural disorders, acquired (e.g. uremia) or congenital

·        Normal BT without suggestive history usually excludes platelet dysfunction. However, a normal BT does not rule out significant defect; with clinical suspicion platelet aggregation should be performed

·        To work up for coagulation disorders in patients, having history of excess bleeding even with normal platelet count.

·        Normal in all other disorders of coagulation except von Willebrand's disease deficiency and some cases of very low plasma fibrinogen.

·        May be useful to monitor treatment of active hemorrhage in patients with prolonged BT due to uremia, Von Willebrand's disease, congenital platelet function abnormalities or severe anemia.

·        No value in performing BT if platelet count < 100,000/cumm as BT is usually prolonged. Prolonged BT with platelet count > 100, 000/cumm usually indicates impaired platelet function (e.g. due to aspirin) or von Willebrand's disease.   

·        Even with a prolonged BT, blood loss does not exceed that of patients with normal BT. Prolonged BT does not necessarily cause increased bleeding.

·        BT increased out of proportion to platelet count suggests von Willebrand's disease or qualitative platelet defect.

Usually prolonged in 

Thrombocytopenia: Platelet count < 100,00/cumm and usually < 80,000/cumm before BT becomes abnormal and < 40,000/cumm before abnormality becomes pronounced.

Platelet function disorders

Hereditary: Von Willebrand's disease, deficient release of platelet glycoproteins, gray platelet syndrome, hereditary hemorrhagic telangiectasia

Acquired: Drugs (aspirin, non- steroidal anti-inflammatory drugs [ NSAIDs], antimicrobials, anticoagulants, anesthetic, calcium channel blockers, β – blockers, phenothiazine, antidepressants), uremia, fibrin degradation products (e.g. disseminated intravascular coagulation [DIC], liver disease, fibrinolytic therapy, immune thrombocytopenias, myeloproliferative disease, vascular disorders, amyloidosis, viral infections, scurvy.

Usually normal in

Hemophilia, severe hereditary hypoprothrombinemia or hypofibrinogenemia.