Factor VII Activity

CPT: 85230
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Test Details

Synonyms

  • Proconvertin

Use

Evaluate an isolated prolonged PT and document factor VII deficiency6-8

Limitations

Direct Xa or thrombin inhibitor therapy may cause factitiously low results. Artifactual elevations in factor VII can occur as the result of cold activation of factor VII in the collection tube prior to analysis.6 Refrigerating or placing on ice for an extended period prior to freezing the plasma can result in the conversion of factor VII to activated factor VIIa.6

Methodology

Factor VII activity is determined utilizing a prothrombin time (PT)-based one-stage clotting time assay. Factor VII-depleted plasma is used as the substrate, and the clotting time with the patient plasma is compared to the clotting time of normal pooled plasma.

Additional Information

Factor VII is a 48 kilodalton single-chain nonenzymatic cofactor that is synthesized in the liver.6 Factor VII is a vitamin K-dependent protein with a plasma concentration of 0.5 mg/mL.6

The plasma half-life of factor VII is short at about four to six hours.6 Factor VII deficiency should be considered when a patient with excessive bleeding has an extended protime (PT) and a normal activated partial thromboplastin time (aPTT). Congenital factor VII deficiency is rare (less than one case per 500,000 individuals) and is inherited as an autosomal recessive trait.6,7 This condition affects both males and females and the prevalence of factor VII deficiency is equal in all ethnic groups.6,7 A few cases of combined congenital factor II, VII, IX, and X factor deficiencies have been reported.6

Symptoms (homozygotes and double heterozygotes) can include mucosal bleeding, epistaxis, postsurgical and postpartum hemorrhage, menorrhagia, gastrointestinal bleeding, and umbilical cord hemorrhage.6-8 Heterozygotes are usually asymptomatic.8 Factor VII plasma activity <30% may result in excessive bleeding following a traumatic event.6 Spontaneous bleeding similar to that observed in severe hemophilia may occur when the activity is <1%;6,7 however, symptomatology does not always correlate with the degree of factor VII deficiency and some patients with low levels may have no bleeding symptoms at all.6,7

Diminished factor VII levels can be seen in patients with significant hepatic dysfunction, with oral anticoagulant (coumarin) therapy, and in individuals with vitamin K deficiency.6,7 Low levels can also be observed in patients with specific factor VII inhibitors and in association with homocystinuria and aplastic anemia.7

High levels of factor VII activity were found to be associated with increased risk for ischemic heart disease events by the Northwick Park Heart Study in 1986;9 however, more recent studies have failed to identify factor VII levels as an independent risk factor for thrombosis.10 A recent consensus conference of the College of American Pathologists on diagnostic issues in thrombophilia did not recommend measurement of factor VII levels for the assessment of thrombotic risk.10

Specimen Requirements

Specimen

Plasma, frozen

Volume

2 mL

Minimum Volume

1 mL

Container

Blue-top (sodium citrate) tube

Patient Preparation

Ideally, the patient should not be on anticoagulant therapy. Avoid warfarin (Coumadin®) therapy for two weeks prior to the test and heparin, direct Xa, and thrombin inhibitor therapies for about three days prior to testing. Do not draw from an arm with a heparin lock or heparinized catheter.

Collection

Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.1 Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio.2,3 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples unless the sample is collected using a winged (butterfly) collection system. With a winged blood collection set a discard tube should be drawn first to account for the dead space of the tubing and prevent under-filling of the evacuated tube.4,5 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternative anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.

Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.

Storage Instructions

Freeze.

Causes for Rejection

Gross hemolysis; clotted specimen; frozen specimen thawed in transit; improper labeling

Clinical Information

Special Instructions

If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted. Refer to Coagulation Collection Procedures for directions.

Footnotes

1. Adcock DM, Kressin DC, Marlar RA. Effect of 3.2% vs 3.8% sodium citrate concentration on routine coagulation testing. Am J Clin Pathol. 1997 Jan; 107(1):105-110. 8980376
2. Reneke J, Etzell J, Leslie S, Ng VL, Gottfried EL. Prolonged prothrombin time and activated partial thromboplastin time due to underfilled specimen tubes with 109 mmol/L (3.2%) citrate anticoagulant. Am J Clin Pathol. 1998 Jun; 109(6):754-757. 9620035
3. National Committee for Clinical Laboratory Standardization. Collection, Transport, and Processing of Blood Specimens for Coagulation Testing and General Performance of Coagulation Assays; Approved Guideline. 5th ed. Villanova, Pa: NCCLS; 2008. Document H21-A5:28(5).
4. Gottfried EL, Adachi MM. Prothrombin time and activated partial thromboplastin time can be performed on the first tube. Am J Clin Pathol. 1997 Jun; 107(6):681-683. 9169665
5. McGlasson DL, More L, Best HA, Norris WL, Doe RH, Ray H. Drawing specimens for coagulation testing: Is a second tube necessary? Clin Lab Sci. 1999 May-Jun; 12(3):137-139. 10539100
6. Adcock DM, Bethel MA, Macy PA. Coagulation Handbook. Aurora, Colo: Esoterix−Colorado Coagulation; 2006.
7. Roberts HR, Escobar MA. Less common congenital disorders of hemostasis. In: Kitchens CS, Alving BM, Kessler CM, eds. Consultative Hemostasis and Thrombosis. Philadelphia, Pa: WB Saunders Co; 2002: 57-71.
8. Triplett DA. Coagulation abnormalities. In: McClatchey KD, ed. Clinical Laboratory Medicine. 2nd ed. Philadelphia, Pa: Lippincott Williams and Wilkins; 2002:1033-1049.
9. Meade TW, Mellows S, Brozovic M, et al. Haemostatic function and ischaemic heart disease: Principal results of the Northwick Park Heart Study. Lancet. 1986 Sep 6; 2(8506):533-537. 2875280
10. Chandler WL, Rodgers GM, Sprouse JT, Thompson AR. Elevated hemostatic factor levels as potential risk factors for thrombosis. Arch Pathol Lab Med. 2002 Nov; 126(11):1405-1414. 12421150

References

Adcock DM, Gosselin R. Direct oral anticoagulants (DOACs) in the laboratory: 2015 review. Thromb Res. 2015 Jul; 136(1):7-12. 25981138

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
800599 Factor VII Activity 3198-9 800599 Factor VII Activity % 3198-9

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