Oro-Maxillofacial Surgery MCQ Answer 9

Best answer is c.

White Blood Cell count (4,500-11,000cells/mm3) normal range.

The white blood cell count expresses the number of WBCs per cubic millimeter of whole blood. WBCs (leukocytes) are classified as either granulocytes (neutrophils, eosinohils, basophils) or non-granulocutyes (lymphocytes, monocytes).

Increased WBCs- extreme temperature, pregnancy, infectious disease (the most common cause for increase), Leukemia.

Decreased WBCs- pernicious anemia (vitamin B12 deficiency), Aplastic anemia (no cell’s produced in the bone marrow), Bone marrow depression secondary to chemo/radiotherapy, Malignant neutropenia or myeloproliferative syndrome (chronic leukemia, polycythemia, thrombocytopenia).

Differential White Cell Count

To identify the various types of leukocytes and their relative amounts in sample, a differential count can be performed. Many labs now use automation to perform this test. The white cells are screened on the basis of 3 sizes: small (normal lymphocytes), middle (monocytes, eosinophils, large lymphocytes variants), and large (neutrophils (stabs & bands)). If one of these cell population fall outside the reference range, the sample is placed on a slide and microscopic differential is performed by a lab technician.

Platelet Count: This test provides a quantitative evaluation of platelet number. Normal counts range from 140,000 to 400,000 platelets/mm3. In most cases, clinical bleeding problems are associated with platelet counts of less than 50,000 platelets/mm3. The average life span of a platelet is 9 to 12 days.

Bleeding Time (BT): This test an assessment of the adequacy of platelet count and function. It is a measure of how long it takes a standardized skin incision to stop bleeding. Depending on the test used, a normal bleeding time ranges from 1 to 6 minutes. Elevated bleeding times are seen with platelet abnormalities.

Prothrombin Time (PT): This test measures the effectiveness of extrinsic coagulation pathway. It is performed by measuring the time it takes to form a clot when calcium and a tissue factor are added to the patient’s plasma. A normal PT indicates normal levels of Factor VII and those factors common to both the intrinsic and extrinsic pathways (V,X, prthrombin and fibrinogen) A normal PT typically ranges from 10 to 15 seconds, and is usually compared to a daily control value. A prolonged PT can be associated with abnormal postoperative coagulation and bleeding. Prolongation of less than one half times the control value is usually associated with mild bleeding disorders, while further prolongation indicates a more severe bleeding disorder. The PT is often used to monitor oral anticoagulant therapy i.e. coumadin.

Coumarin is a vitamin K antagonist. Vitamin K is necessary for final activation of factors II(prothrombin), VII, IX, and X.

International Normalized Ratio (INR) For patients on chronic oral anticoagulants, i.e. coumarin, the INR is now gaining acceptance for the reporting of prothombin time ratio

(PTR), that is the patient’s PT compared to the lab’s PT. The INR allows comparison from one hospital to another, especially in the studies of the ideal therapeutic range of PTR. By using an international sensitivity index (ISI) which is determined for each batch of reagent and is specific to the lab’s particular equipment, the calculation of INR = (patient PT/normal PT) ISI. For most conditions that require ongoing anticoagulation therapy, the American Heart Association has recommended INR levels between 2.0 and 3.0.

Partial Thromboplastin Time (PTT): This test measure the effectiveness of the intrinsic coagulation pathway. It test all factors except Factor VII. The test is performed by measuring the time it takes to form a clot after addition of kaolin, a surface acting cephalin (a substitute for platelet factor), to the patient’s plasma. A normal value typically ranges from 25 to 35 seconds, and is usually compared with a daily control.

PTT values 5 to 10 seconds above the upper limit of normal may be associated with mild bleeding abnormalities, while higher values are associated with significant bleeding risks. PTT is often used to monitor heparin therapy.

Thrombin Time (TT): This test measures the time it takes thrombin to convert fibrinogen to fibrin, which constitutes the essential components of a blood clot. The TT is a fairly good test to identify fibrinolysis disorders. Normal TT values range from 9 to 13 seconds and are compared with a laboratory control. Results in excess of 16 to 18 seconds are considered prolonged.

REF: Oral Diagnosis Laboratory Studies Hematolgic Screening and Evaluation of Hemostasis.