Continued...

History and clinical examination

Laboratory investigations in a bleeding disorder:
The initial laboratory studies to evaluate a suspected bleeding disorder should include a complete blood count (CBC) with platelet counts as well as a review of the smear, especially for clumping of platelets and confirmation of the platelet count obtained on the counter. In addition, tests such as Prothrombin time (PT), an activated Partial thromboplastin time (aPTT), Thrombin time, plasma fibrinogen levels and factor XIII assay are important in arriving at a specific diagnosis. Results of these tests will determine subsequent studies to be obtained.

Complete Blood count :
The complete blood count offers at least two important pieces of information. It allows for rapid determination of the platelet count, either confirming or rejecting a suspected thrombocytopenia. Anemia in association with a history of bleeding symptoms could suggest prolonged blood loss. A microcytic anemia, indicative of iron deficiency, may represent a history of prolonged blood loss, not compensated for by normal dietary iron intake. Alternatively, a normocytic anemia may be seen in cases of recent hemorrhage, blood loss. On the other hand, a normocytic or macrocytic anemia may suggest a hemolytic anemia e.g. in Evan's syndrome (Autoimmune Hemolytic Anemia & ITP). Apart from anemia, if leucopenia is also present along with thrombocytopenia, it raises the suspicion of bone marrow failure syndromes as seen in aplastic anemia, leukemia and lymphoma.

Peripheral blood smear :
Peripheral blood smear should be examined in every patient with a suspected platelet disorder. Examination of the smear allow for corroboration of platelet counts obtained on an automated cell counter as well as looking at platelet morphology. In platelet functional disorders such as Glanzmann's thrombasthenia, Bernard-Soulier Syndrome, platelets will be seen isolated with no clumps on smear (confirm non EDTA smear) In the giant platelet disorders such as Bernard-Soulier or May- Hegglin anomaly, the majority of platelets will be of a size similar to or larger than the erythrocytes. On a smear from a patient with the much more common ITP, both normal and large platelets are seen. Conversely, the Wiskott-Aldrich syndrome is characterized by smaller-than-normal platelet volume. The mean platelet volume is often reported as part of an automated complete blood count but may not accurately reflect the actual platelet size, particularly in the presence of thrombocytopenia.

PT and aPTT :
The PT and aPTT are screening tests for the second phase of hemostasis. PT evaluates the extrinsic (factor VII) and common pathway (factor X, V and II) of the coagulation cascade, whereas the aPTT evaluates the intrinsic (factors VIII, vWF, IX, XI and XII) and common pathways. PT is often reported as an international normalized ratio (INR), a standard allowing for the comparison of results between different laboratories. Prolongation of the PT or aPTT is indicative of a factor deficiency. The factor level at which either the PT or aPTT becomes prolonged varies but is usually around 40% of normal pooled plasma levels for any given factor.

APTT and PT mixing studies :
An abnormal PT or aPTT should be followed by a mixing study, the results of which will indicate either the presence of an inhibitor or a factor deficiency. By mixing equal volumes of a patient's plasma with normal plasma, any factor deficiency should be corrected to a minimum of 50% levels; hence, the normalization of the PT or aPTT following a mixing study indicates a factor deficiency. Persistent prolongation of the test result after mixing with normal plasma is indicative of the presence of an inhibitor (usually an antibody against one or more coagulation factors). If BaSO4 adsorbed plasma is added to patient's plasma, and the aPTT normalizes, it indicates factor VIII deficiency, if aged serum added to patient's plasma normalizes the aPTT, it indicates factor IX deficiency. If it normalizes with both, it is suggestive of factor XI deficiency. When aPTT mixing studies indicate a factor deficiency, it is necessary to measure factors VIII, IX and XI because deficiencies of these factors are associated with clinical bleeding. Decreased concentration of factor XII, prekallikrein, and high molecular weight kininogen also can cause a prolongation of the aPTT; however these deficiencies are not associated with bleeding. If there is a prolongation of aPTT and platelets are not in clumps on the peripheral smear, it strongly suggests vWF deficiency.

Thrombin time (TT) :
A prolonged TT signifies low fibrinogen activity (hypofibrinogenemia or dysfibrinogenemia), the presence of fibrin spilt products, or heparin contamination. The reptilase clotting time is similar to the thrombin time, except that the coagulation induced by this enzyme from snake venom is not inhibited by heparin. For this reason, utilizing TT and reptilase clotting time together can help clarify whether abnormal coagulation results are due to heparin contamination.

Appendix 2 shows the interpretation of various coagulation tests & Appendix 3 & 4 depict the mixing studies.