10, 11 Beginning of clotting, End of clotting

Whole-blood clotting time (Lee–White): beginning and end of clotting, normal range, causes and limitations.

The whole-blood clotting time (Lee–White method) measures how long it takes for fresh venous blood, without anticoagulant, to clot in glass tubes at 37 °C. The beginning of clotting is the moment when the first clot appears; the end of clotting is when the blood forms a firm clot and the tube can be inverted. The test reflects the overall activity of the coagulation factors, mainly of the intrinsic pathway, and is influenced by platelets and haematocrit. It is one of the oldest coagulation tests (1913). Today it has largely been replaced by standardised tests: PT/INR, activated partial thromboplastin time (aPTT), fibrinogen and viscoelastic tests.

CoagulationHaemostasisScreening

Normal (Lee–White)≈ 5–10 min (method-dependent)

In this appclotting up to 9 min

Beginning–end intervalshould exceed 30 s

Modern equivalentsaPTT, PT/INR, fibrinogen

Figure 1. Whole-blood clotting time zones. Reference values depend on tube material, temperature and technique, so each laboratory sets its own range.

How coagulation works

According to the modern cell-based model, coagulation starts when tissue factor on injured cells meets factor VII. A small amount of thrombin is formed and activates platelets and cofactors (amplification). A large burst of thrombin is then generated on the platelet surface (propagation) and converts fibrinogen into fibrin. In parallel, the plasma kallikrein–kinin system links coagulation with inflammation, vascular permeability and pain.

Prolonged clotting time

Heparin and other anticoagulants
Severe deficiency of coagulation factors: haemophilia A or B, liver disease, vitamin K deficiency
Disseminated intravascular coagulation, very low fibrinogen
Circulating inhibitors (for example antibodies to factor VIII)

The test is insensitive: mild factor deficiencies and platelet disorders may give normal results. A short clotting time is not a reliable sign of thrombosis risk.

What to do

An abnormal clotting time, unusual bruising, nosebleeds, heavy periods or prolonged bleeding after injury or dental work should be investigated with standard coagulation tests (PT/INR, aPTT, fibrinogen, platelet count).

References

Lee RI, White PD. A clinical study of the coagulation time of blood. Am J Med Sci. 1913;145:495–503.
Hoffman M, Monroe DM. A cell-based model of hemostasis. Thromb Haemost. 2001;85(6):958–965. doi:10.1055/s-0037-1615947

This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.

Published on 9 May 2024