Clotting Time by Lee-White

Patient Care / Preparation

• Ensure a minimum of three hours without heparin therapy before collecting the sample.
• Avoid traumatic venipuncture as it can affect results.

Specimen

• Type: Whole Blood
• Container: Three 12 x 75 mm glass test tubes and a plastic syringe

Collection Procedure

1. Use the two-syringe method for accurate blood sampling.
2. Draw blood into a plastic syringe.
3. Fill each of the three test tubes with 1 mL of blood.
4. Maintain tubes at 37°C during the procedure.
5. Start the stopwatch after the third tube is filled.
6. Stop timing when the blood in the last tube clots.

Sample Rejection Criteria

• Sample drawn within 3 hours of heparin therapy
• Traumatic venipuncture

Reference Range

Normal Clotting Time: 8 to 15 minutes

Clinical Use

• Evaluate the overall coagulation system
• Monitor heparin therapy, especially where APTT may be unavailable

Limitations of the Test

• Significantly prolonged clotting time if drawn <3 hours after heparin
• Test lacks standardization across technologists/laboratories
• Reduced accuracy for longer clotting times
• Many labs no longer perform this test due to variability and better alternatives

Methodology

Time measurement begins after blood is freshly drawn and exposed to a standardized activation stimulus. The endpoint is the visual detection of clot formation.

Additional Information

• Effective for tracking heparin therapy, though less reliable as a standalone indicator
• Heparin’s anticoagulant activity is dependent on antithrombin III (AT III) activation
• In AT III deficiency, plasma infusion may be needed for heparin to work
• In DIC (Disseminated Intravascular Coagulation), results can be misleading
• In cases of severe lipemia, lipase may compete with heparin, affecting efficacy
• Test results may be influenced by reagent additives such as phospholipids or contact activators used in other tests like APTT

References

1. Sirridge MS and Shannon R, Laboratory Evaluation of Hemostasis and Thrombosis, 3rd ed. Lea & Febiger, 1983: pp. 68, 112–115.
2. Jacobs, Demott, Finley, Horvat, Kasten JR, Tilzer, Laboratory Test Handbook. Lexi-Comp Inc, 1994.