From: Elizabeth M. Van Cott, M.D., and Michael Laposata, M.D., Ph.D., "Coagulation." In: Jacobs DS et al, ed. The Laboratory Test Handbook, 5th Edition. Lexi-Comp, Cleveland, 2001; 327-358.

Index of Tests

Prekallikrein [CO002600]

Related Information

Synonyms Fletcher Factor

Applies to Kallikrein

Abstract Prekallikrein is a coagulation protein involved in the early stages of intrinsic pathway activation. Prekallikrein deficiency can cause a marked prolongation of the PTT, but it does not cause bleeding. The same is true for factor XII deficiency and high-molecular weight kininogen (HMWK) deficiency.

Patient Preparation Patients cannot be on hirudin or argatroban anticoagulation, which can interfere with mixing studies and PTT-based prekallikrein assays. Danaparoid may also interfere with these assays. If heparin is present, notify the laboratory because heparin must be removed prior to testing.

Specimen Plasma

Container One blue top (sodium citrate) tube

Collection Routine venipuncture. If multiple tests are being drawn, draw blue top tubes after any red top tubes but before any lavender top (EDTA), green top (heparin), or gray top (oxalate/fluoride) tubes. Immediately invert tube gently at least 4 times to mix. Tubes must be appropriately filled. Deliver tubes immediately to the laboratory.

Storage Instructions Separate plasma from cells as soon as possible. If assay is not performed within 4 hours, freeze plasma specimen.

Causes for Rejection Specimen received more than 4 hours after collection, tubes not filled, clotted specimens

Turnaround Time Less than 1 day (longer if test is a send-out)

Reference Interval 60% to 140% of normal. Newborns have lower levels than adults; the values increase to near adult normal range by age 6 months.1

Use May be performed when a routine prolonged PTT evaluation finds no explanation for the prolongation (see Mixing Studies). The PTT is normal in the mixing study; factors VIII, IX, XI, and XII are normal; the PT and fibrinogen are normal; and lupus anticoagulant assays are negative. If prekallikrein assays are normal, HMWK assays may be considered.


Screening assay: Preincubate a PTT test sample for 10 minutes prior to adding calcium. A prolonged PTT that shortens after the 10-minute incubation is suspicious for a prekallikrein deficiency. In addition, if a PTT is performed with ellagic acid as the intrinsic pathway activator, the PTT will usually be normal in prekallikrein deficiencies.

Specific factor assay for prekallikrein: Can be performed similar to other coagulation factor assays. Patient plasma is mixed with prekallikrein-deficient plasma and a PTT is performed on the mixture. The amount of prekallikrein in the patient plasma is determined from a standard curve that plots known amounts of prekallikrein against PTT values. Note: PTT tests are normally incubated for 3 minutes prior to adding calcium. When using the PTT in a prekallikrein factor assay, the incubation period is shortened to 1 minute.2 A chromogenic prekallikrein assay is also available.

Additional Information Prekallikrein is one of the contact factors that participates in the activation of the intrinsic pathway of coagulation when blood is exposed to a negatively charged foreign surface. With contact activation, activated factor XII (XIIa) converts prekallikrein into kallikrein. Kallikrein then activates more factor XII. HMWK acts as a cofactor in both of these reactions. HMWK also acts as a cofactor in the activation of factor XI by factor XIIa. Kallikrein releases bradykinin from HMWK, which has vasoactive activities. Fibrinolysis is also activated by contact activation. Recent evidence suggests that, in vivo, activation of prekallikrein occurs before activation of factor XII.

Prekallikrein deficiency is rare and does not cause bleeding, despite prolongation of the PTT. The lack of bleeding is presumably because the extrinsic pathway of coagulation, via factor VII and tissue factor, remains intact, and factor XI can be activated by thrombin generated from the extrinsic pathway.3,4 Thus, factor XI can be activated without the need for prekallikrein, HMWK, or factor XII. This is consistent with the observation that deficiencies of the latter three factors are not associated with bleeding.

Acquired, usually mild-to-moderate decreases in prekallikrein may be found in liver disease or disseminated intravascular coagulation (DIC). Rarely, a prekallikrein inhibitor (antibody) has been reported.5


1. Andrew M, Paes B, and Johnston M, "Development of the Hemostatic System in the Neonate and Young Infant,"Am J Pediatr Hematol Oncol, 1990,12(1):95-104.

2. Sibley C and Evatt BL, "Laboratory Suggestions: Improving the Sensitivity of the Fletcher Factor Assay,"Am J Clin Pathol, 1979, 71(5):570-3.

3. Naito K and Fujikawa K, "Activation of Human Blood Coagulation Factor XI Independent of Factor XII. Factor XIa Is Activated by Thrombin and Factor XIa in the Presence of Negatively Charged Surfaces,"J Biol Chem, 1991, 266(12):7353-8.

4. Gailani D and Broze GJ, "Factor XI Activation in a Revised Model of Blood Coagulation,"Science, 1991, 253(5022):909-12.

5. Page JD, DeLa Cadena RA, Humphries JE, et al, "An Autoantibody to Human Plasma Prekallikrein Blocks Activation of the Contact System,"Br J Haematol, 1994, 87(1):81-6.


Sanfelippo MJ, Carafo AJ, and Hollister WN, "APTT Prolonged by Prekallikrein Deficiency,"Lab Med, 1998, 29(5):274-6.

Schmaier AH, Rojkjaer R, and Shariat-Madar Z, "Activation of the Plasma Kallikrein/Kinin System on Cells: A Revised Hypothesis,"Thromb Haemost, 1999, 82(2):226-33.


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