Screening Tests: Introduction
Haemostatic screening tests e.g. Prothrombin Time (PT) and the Activated Partial Thromboplastin Time (APTT) undertaken to establish whether someone is at risk of bleeding in advance of surgery or an invasive procedure, can be misleading. Such tests can generate normal results even in individuals with significant derangements of haemostasis. It is important to remember that the laboratory tests are in vitro tests and may not necessarily reflect the underlying haemostatic mechanism.
The most important screening test in haemostasis is the patient’s personal bleeding history (if this can be considered a test) , their use of anti-thrombotic drugs including anti-platelet agents and whether there is any significant family history suggestive of an inherited bleeding diathesis.
Ordering a screening test before taking a thorough history and examining the patient is inappropriate.
The use of a structured bleeding state questionnaire has been validated in Type 1 VWD and more recently in a patients referred for investigation of a suspected bleeding disorder [see References] and these provide an invaluable series of questions for the assessment of bleeding risk.
In the UK the National Centre for Clinical Excellence (NICE) and the British Committee for Standards in Haematology (BCSH) have both addressed the value of screening tests in haemostasis.
The tests that are commonly used as screening tests are:
- Prothrombin Time (PT)
- Activated Partial Thromboplastin Time (APTT)
The fibrinogen concentration and thrombin time are not generally considered to be first-line screening tests although they are commonly performed.
It is important that the platelet count is checked in any patient undergoing haemostatic investigations.
Click HERE to go to the Data Interpretation Exercises.