Lab Tests Diagnostic Medical Tests Medical Lab Tests
 Red blood cell count
 Red cell indices
 sedimentation rate
 Reticulocyte count
 Osmotic fragility
 Total hemoglobin
 Fetal hemoglobin
 Sickle cell test
 Unstable hemoglobin
 Heinz bodies
   Iron and total
 iron-binding capacity
 White blood cell count
   White blood cell
 Bleeding time
 Platelet count
 Capillary fragility
 Platelet aggregation
   Activated partial
 thromboplastin time
 Prothrombin time
 Activated clotting time
   One-stage factor
 coagulation system
   One-stage factor
 coagulation system
 Plasma thrombin time
 Plasma fibrinogen
 Fibrin split products
 Plasma plasminogen
 Protein C
 Euglobulin lysis time
 normalized ratio

Home :: Extrinsic coagulation system

One-Stage Factor Assay: Extrinsic Coagulation System

When prothrombin time (PT) and activated partial thromboplastin time (APTT) are prolonged, a one-stage assay is used to detect a deficiency of factor II, factor V, or factor X. If PT is abnormal but APTT is normal, factor VII may be deficient.


  • To identify a specific factor deficiency in persons with prolonged PT or APTT . To study patients with congenital or acquired coagulation defects.
  • To monitor the effects of blood component therapy in factor-deficient patients.

Patient preparation

  • Explain to the patient that this test is used to assess the function of the blood coagulation mechanism.
  • Tell him that a blood sample will be taken. Explain who will perform the venipuncture and when.
  • Reassure him that drawing a blood sample will take less than 3 minutes.
  • Explain that he may feel slight discomfort from the tourniquet pressure and the needle puncture.
  • When the patient is factor deficient and receiving blood component therapy, tell him that he may need a series of tests.
  • Withhold oral anticoagulants before the test. If they must be continued, note this on the laboratory slip.
  • Inform the patient that food or fluids need not be restricted before the test.

Procedure and posttest care

  • Perform a venipuncture, and collect the sample in a 7-ml blue-top tube.
  • If a hematoma develops at the venipuncture site, apply warm soaks.
  • A patient with a bleeding disorder may require a pressure bandage to stop bleeding at the venipuncture site.
  • If the patient has a suspected coagulation defect, avoid excessive probing during venipuncture; don't leave the tourniquet on too long (it will cause bruising); and apply pressure to the puncture site for 5 minutes or until the bleeding stops.
  • Completely fill the collection tube, and invert it gently several times to mix the sample and the anticoagulant.
  • Handle the sample gently to prevent hemolysis, and send it to the laboratory immediately, or place it on ice.

Reference values

Diluted samples of the patient's plasma are added to a substrate plasma deficient in a single factor. The activity of this mixture is compared with normal activity. The reference ranges for the factors are as follows:

  • factor II: 80% to 120% of normal
  • factor V: 50% to 150% of normal
  • factor VII: 65% to 140% of normal
  • factor X: 45% to 155% of normal.
Abnormal findings

If the clotting time for the substrate mixture is prolonged compared to normal, the patient may be deficient in the factor being tested. Deficiency of factor II, factor VII, or factor X may indicate hepatic disease or vitamin K deficiency. Deficiency of factor X may also indicate disseminated intra vascular coagulation (DIC). Factor V deficiency suggests severe hepatic disease, DIC, or fibrinogenolysis. Deficiencies of all four factors may be congenital; absence off factor II is lethal.

Interfering factors

  • Failure to mix the sample and the anticoagulant adequately, or to send the sample to the laboratory immediately or place it on ice.
  • Hemolysis due to rough handling of the sample.
  • Oral anticoagulants (possible increases due to inhibition of vitamin K­ dependent synthesis and activation of tilling factors II, VII, and X, which form in the liver).

Diagnostic Medical Tests
Medical Tests
Dagnostic Tests
Lab Tests

Contact us | Link to us | Lab tests
Resources - 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11
(c)Copyright All rights reserved.

The information provided on this web site should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. We will not be liable for any complications, or other medical accidents arising from the use of any information on this web site.