What are other Names for this Test? (Equivalent Terms)
- Fitzgerald Factor and Prekallikrein Blood Test
- High-Molecular-Weight Kininogen and Fletcher Factor Blood Test
- HMWK and PK Blood Test
What is HMWK and Prekallikrein Blood Test? (Background Information)
- High-molecular-weight kininogen (HMWK) and prekallikrein (PK) are proteins involved in the formation of blood clots at the site of blood vessel injury. Blood clots stop blood loss and allow the blood vessel to continue functioning
- The clotting process starts with an injury to a blood vessel, which causes it to constrict. Called the vascular phase, this is the first reaction of a blood vessel to damage. Constriction of a blood vessel reduces the flow of blood to the site of injury, which minimizes blood loss
- Next, circulating platelets clump along the site of blood vessel injury. The platelets form a foundation for a blood clot and release chemicals that stimulate clotting
- The coagulation phase then causes a blood clot to form. Clotting occurs when an enzyme, called thrombin, converts a soluble protein, fibrinogen, into its insoluble form, fibrin. Fibrin proteins make up the bulk of a blood clot
- Thrombin is activated by the merging of two pathways, called the intrinsic and extrinsic pathways, into the common pathway. These are initiated by different parts of the body after blood vessel damage:
- The intrinsic pathway begins in blood with the activation of circulating proteins
- The extrinsic pathway begins in the blood vessel with the release of protein factors by damaged cells lining the vessel
- The extrinsic pathway is the first to activate. The intrinsic pathway then reinforces the extrinsic pathway and provides longer-lasting clotting effects. HMWK and prekallikrein proteins help start the intrinsic pathway
- Once a coagulation factor is activated, it remains active. Thus, with each step in the pathway, more and more factors are activated. This results in a cascade of events similar to a snowball effect
- A counter pathway ensures that the size of the growing blood clot stays in check. Problems with this regulatory pathway may lead to a dangerous condition where a blood clot forms within blood vessels (thrombosis)
- The HMWK and Prekallikrein Blood Test helps determine the levels of HMWK and prekallikrein in blood. It is used to diagnose very rare genetic disorders that interfere with blood clotting
What are the Clinical Indications for performing the HMWK and Prekallikrein Blood Test?
Following are the clinical indications for performing the HMWK and Prekallikrein Blood Test:
- Following up to a prolonged value for the PTT blood test
- Family history of clotting disorders
- Excessive bleeding
How is the Specimen Collected for HMWK and Prekallikrein Blood Test?
Following is the specimen collection process for HMWK and Prekallikrein Blood Test:
Sample required: Blood
Process of obtaining blood sample in adults:
- A band is wrapped around the arm, 3-4 inches above the collection site (superficial vein that lies within the elbow pit)
- The site is cleaned with 70% alcohol in an outward spiral, away from the zone of needle insertion
- The needle cap is removed and is held in line with the vein, pulling the skin tight
- With a small and quick thrust, the vein is penetrated using the needle
- The required amount of blood sample is collected by pulling the plunger of the syringe out slowly
- The wrap band is removed, gauze is placed on the collection site, and the needle is removed
- The blood is immediately transferred into the blood container, which has the appropriate preservative/clot activator/anti-coagulant
- The syringe and the needle are disposed into the appropriate “sharp container” for safe and hygienic disposal
Preparation required: No special preparation is needed prior to the test.
What is the Significance of the HMWK and Prekallikrein Blood Test Result?
A low value for the HMWK and Prekallikrein Blood Test is interpreted from an HMWK level of less than 59% and a prekallikrein level of less than 55%. It may indicate:
- Rare congenital deficiencies of clotting proteins
- No bleeding diathesis associated with deficiencies
The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.
Additional and Relevant Useful Information:
- In general, HMWK and prekallikrein deficiency due to genetic causes is extremely rare
Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider of the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.
The following DoveMed website links are useful resources for additional information:
Please visit our Laboratory Procedures Center for more physician-approved health information: