Importance of coagulation screening test

The screening coagulogram is a small group of commonly available baseline tests used to access the hemostatic system in two main situations. The first of these is preoperative work up of a patient before a minor or major surgery. In this situation the aim of coagulation screen is to exclude with reasonable confidence, the likelihood of serious bleeding during surgery or the post operative period. The other common scenario is when a patient with abnormal bleeding is referred for diagnostic testing, usually if no structural causes of blood loss have been found. Here the coagulation screening test results help pinpoint a broad area of hemostasis to be tested further and thus streamline further tests.

The bleeding history: Components and Their Significance

• Gender of the patient: Males more likely to suffer from X linked recessive disorders.
• Age at the onset of bleeding: Younger age is more likely in an inherited cause.
• Sites of bleeding: Muco-cutaneous bleeds suggest platelet number or function or vessel wall defect. Articular, muscle or fascial plane bleeds suggest severe coagulation factor deficiencies. Coexistent serious medical, surgical or oncological disorders or obstetric state increase the likelihood of acquired platelet or coagulation disorders. History of umbilical cord stump bleeding suggests a serious disorder of diminished clot strength and stability. Family history of bleeding may suggest inheritance pattern. Requirement of blood transfusion virtually always indicates serious bleeding requiring evaluation.
• History of intake of medications: Drug induced thrombocytopenia, anticoagulant drugs.
• Menstrual history: Excess losses may be ignored by the patient as normal.
• Mental state examination: Bleeding may be self-inflicted or abuse related.

Screening tests of hemostasis (platelet count, PT, aPTT) are useful in suggesting diagnostic possibilities in bleeding patients. However, normal values do not altogether exclude bleeding disorders. Isolated, prolonged PT may have inherited or acquired causes: liver disease, warfarin therapy, DIC, Factor VII deficiency. Isolated, prolonged aPTT suggest heparin therapy, deficiency or inhibitor to factors VIIII, IX, XII or XI. Prolongation of both the PT and aPTT suggest either acquired multiple factor deficiency (DIC, vitamin k deficiency) or heparin or warfarin therapy or inherited deficiency of a common pathway factor.

Key recommendations of the BCSH guidelines for the assessment of bleeding risk prior to surgery or invasive procedures:

1. It is not recommended indiscriminate coagulation screening before surgery or other invasive procedures to predict postoperative bleeding in unselected patients.
2. A bleeding history including detail of family history, previous excessive post traumatic or postsurgical bleeding and use of antithrombotic drugs should be taken in all patients preoperatively and prior to invasive procedures.
3. If the history of bleeding is negative, then no further coagulation testing is required.
4. If the history of bleeding is positive or there is a clear indication of liver disease, then a comprehensive assessment is required. Determine bleeding risk as follows:
• Low: Non vital organs involved, exposed surgical site, limited dissection e.g. dental extraction
• Moderate: Vital organs involved, deep/extensive dissection e.g. GI resections, LSCS
• High: Bleeding likely to compromise surgical results, bleeding complications frequent e.g. orthopedic surgery, intraocular explorations
Screen as follows:
• Low bleeding risk: History alone
• Moderate or High bleeding risk: History +PT +aPTT +Platelet count

Approach to Screen detected abnormality Hematologists.

• History and examination negative and screening test positive: Repeat PT, aPTT, TT, platelet count, peripheral smear, LFT, KFT.
• History positive, any screening test result: In addition to the above, consider (case based) platelet function tests, von Willebrand antigen, ristocetin cofactor, Factor VIII, Factor IX, Factor XI, clot solubility test.
• Fasting State of the patient: Currently, most laboratory instruments detect clot formation with automated photo optical detection systems that record changes in light transmittance. However, plasma turbidity can interfere with instruments optical system and cause artifactual results as it does in non-fasting lipaemic plasma specimens and in hemolyzed or icteric specimens.

Clinicians can adequately instruct patients on the importance of fasting. Before undertaking the complex investigation of prolonged PT and APTT Test, clinicians should consider repeating the testing to exclude artifactual results. After appropriate sample collection, it is the coagulation laboratory's responsibility to avoid artifactual results. Therapeutic or surreptitious use of vitamin k antagonist (e.g. warfarin) results in prolongation of the PT and mild prolongation of the APTT. Therapeutic intravenous administration of unfractionated heparin or its presence within central venous catheters through which the samples may have been collected, results in prolonged APTT. Hence, in case the results appear to be extremely prolonged then additional testing is reasonable.

Next step

After artifactual results and anticoagulants have been excluded, a thorough clinical assessment should be taken (if not previously done) to identify systemic diseases that may prolong PT or APTT (e.g. liver disease, connective tissue disease or DIC and fibrinolysis).