Prekallikrein (Fletcher Factor) Assay

CPT: 85292
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  • Fletcher Factor Assay

Expected Turnaround Time

4 - 8 days

Related Documents

For more information, please view the literature below.

Procedures for Hemostasis and Thrombosis: A Clinical Test Compendium

Specimen Requirements


Plasma, frozen


2 mL

Minimum Volume

1 mL


Blue-top (sodium citrate) tube


Citrated plasma samples should be collected by double centrifugation. 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, except when using a winged blood collection device (ie, "butterfly"), in which case a discard tube should be used.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 alternate 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. Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells. Deliver to a plastic transport tube, cap, and recentrifuge for 10 minutes. Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube. Transfer the plasma into a Labcorp PP transpak frozen purple tube with screw cap (Labcorp No. 49482). Freeze immediately and maintain frozen until tested. 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. Stable at room temperature for four hours.

Patient Preparation

Do not draw from an arm with a heparin lock or heparinized catheter.

Test Details


Measurement of prekallikrein factor concentration


Factor prekallikrein activity is determined utilizing an aPTT-based one-stage clotting time assay. Factor prekallikrein-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

Prekallikrein is a single-chain serine protease synthesized in the liver that circulates in two forms having molecular weights of 85 and 88 kilodaltons.6 Prekallikrein's plasma concentration is 35 to 45 mg/mL. It circulates in an equimolar complex with high molecular weight kininogen (HMWK), and has a plasma half-life of 24 hours. Kallikrein liberates kinins from kininogens, activates factor XII and plasminogen, converts protein to renin, destroys C1 components, and interacts with leukocytes.

Factors VIII, IX, XI, XII, prekallikrein, and high molecular weight kininogen (HMWK) are the coagulation factors of the intrinsic coagulation pathway. Factor XII, high molecular weight kininogen, and prekallikrein are also called the “contact” factors. Factor XI is sometimes included in this designate of “contact” factors because of its interaction with others listed. Factor XI is activated by factor XIIa formed through activation of XII by a HMWK-prekallikrein complex on endothelial cells. With production of XIIa and kallikrein, activation of kinin, fibrinolytic, and complement systems occur. The major inhibitor of XIIa and kallikrein is C1 inhibitor. Other inhibitors include antithrombin (AT), plasminogen activator inhibitor (PAI), and α2-macroglobulin.

Contact factor deficiencies have no hemorrhagic consequence; however, the contact factors are necessary for normal aPTT clot formation in the laboratory. Deficiency of prekallikrein produces markedly prolonged aPTT results. Hereditary prekallikrein deficiency conditions are inherited through an autosomal recessive pattern. Although the aPTT is prolonged in deficiencies of factor XII, prekallikrein, and high molecular weight kininogen, there is generally no clinical evidence of bleeding unless other contributing factors are present. These deficiencies are generally diagnosed when evaluating a prolonged aPTT with no other explanation (ie, other screening test) and clinical history is negative for a bleeding disorder.


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; 107(1):105-110. 8980376
2. Reneke J, Etzell J, Leslie S, et al. 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; 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; 107(6):681-6683. 9169665
5. McGlasson DL, More L, Best HA, et al. Drawing specimens for coagulation testing: Is a second tube necessary? Clin Lab Sci. 1999; 12(3):137-139. 10539100
6. Adcock DM, Bethel MA, Macy PA. Coagulation Handbook. Aurora, Colo: Esoterix−Colorado Coagulation; 2006.


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
500194 Prekallikrein Assay 500195 Prekallikrein Assay % 52759-8

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