Bleeding time test: why it has fallen out of use and what replaced it

When a blood vessel is cut, platelets stick to the wound and clump to plug it. A bleeding time test tries to measure how well that works in the living body. Lab Tests Online UK explains that, in the past, the primary screen for platelet dysfunction was the bleeding time test, which involves making two small, shallow, standardised cuts on the inner forearm and measuring how long bleeding takes to stop.

Its appeal was that it is the only test that directly measures platelet function within the body: all the other platelet function tests are indirect, taking platelets out in a blood collection tube and testing their response in vitro.

The same source says the bleeding time procedure has fallen from favour in recent years, that many hospitals no longer offer it, and that several national organisations have issued position statements against its routine use. The reasons given: it is not sensitive or specific, it does not necessarily reflect the risk or severity of surgical bleeding, it is poorly reproducible, it can be affected by aspirin and by the skill of the person performing it, and it frequently leaves small, thin scars on the forearm.

In other words, a normal bleeding time did not guarantee safe surgery and a long one did not always mean a real bleeding disorder. Modern practice avoids a test that can mislead and mark the skin.

The first steps are a careful history (family bleeding history, medicines, heavy periods, bleeding after dental work), a full blood count including the platelet count, and the clotting screen of PT and aPTT. Lab Tests Online UK says that platelet count requests include unexplained or easy bruising, prolonged bleeding, and petechiae or purpura (small red or purple spots in the skin); the count only shows platelet number, not how well they work.

If those are normal and suspicion remains, platelet function tests are done. They include platelet aggregometry, carried out only in specialised, larger hospital laboratories because of its complexity and the need for specialist staff, and which involves collecting around 30 mL of blood from which platelet-rich plasma is made and mixed with substances that activate platelets, and analysers that test platelet plugging under flow. The coagulation factor assays and von Willebrand tests may follow.

Lab Tests Online UK says you may be instructed to refrain from drugs that affect platelet function, such as aspirin and non-steroidal anti-inflammatory drugs including ibuprofen, naproxen and COX-2 inhibitors, and over-the-counter products containing them, but you must not stop any medicine unless your health care provider tells you to. Blood is taken from a vein in the arm with a needle.

Platelet function testing may be requested when you bruise easily or have excessive or prolonged bleeding, take medicines that can alter platelet function, or before or during certain surgeries.

If your notes mention a historic bleeding time, treat it with caution because of the test's limits. Abnormal platelet function can be inherited (rare conditions such as Glanzmann thrombasthenia and Bernard-Soulier syndrome, named in the platelet count guide) or acquired through medicines, kidney disease or liver disease. Von Willebrand disease is a common inherited bleeding disorder assessed with specific blood tests.

Seek urgent help rather than waiting for tests if bleeding is heavy or will not stop, after a head injury, or if you vomit blood or pass black stools; call 999 or go to A&E.

See your GP, who will take a history, check medicines and arrange blood tests. Mention any family history of bleeding, heavy or long periods and bleeding after surgery. A haematology referral follows if tests suggest a platelet, clotting factor or von Willebrand problem.