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In follow up to the previous question, the upper image again illustrates the colonies recovered from the blood culture bottle. The colonies are small, transluscent, gray-yellow, and surrounded by a wide zone of beta hemolysis.The size of the colonies compared to the zones of hemolysis suggests a group A streptococcus.The susceptibility to bacitracin (zone of inhibition around the "A" disk)(lower photograph) is virtually diagnostic of a group A streptococcus.The absence of a zone of inhibition around the SXT disk indicates resitance to sulfamethoxazole/ trimethoprim. SXT resistance is also shared by group B streptococci, which are, however, resistant to bacitracin.The resistance to SXT is used for the primary recovery of groups A and B streptococci from specimens with mixed culture. Their resistance allows them to selectively grow out from contaminating bacteria that are inhibited by this antibiotic.

The prothrombin time is a screening test that helps to assess the functionality of both the extrinsic and common pathways. The effectiveness and presence of factors I, II, V, VII, and X are assayed in this diagnostic test, as they are all found in the aforementioned pathways. The results of the prothrombin time are used in conjunction with other diagnostic tests, as well as the clinical picture of the patient, to determine any hemostatic abnormalities which may be present. In addition to being an integral part of the coagulation disorder assessment process, the PT is also used to determine therapeutic effectiveness of oral anticoagulants, by monitoring drugs such as Warfarin, Coumarin, and Dicoumarol. Prothrombin time test results are reported as the number of seconds needed for a clot to form in the patient specimen using the laboratory's instrument/reagent system, and as the International Normalized Ratio (INR).

The presence of D-dimers in plasma or whole blood indicates that fibrin has been formed and degraded (fibrinolysis). Plasmin can also degrade intact fibrinogen, generating fibrinogen degradation products that are detected in fibrin/fibrinogen degradation products (FDP) assays. D-dimers and FDP can become elevated whenever the coagulation and fibrinolytic systems are activated. The presence of D-dimer confirms that both thrombin and plasmin have been generated since it can only be produced as the result of the plasmin degradation of fibrin. This makes the test for D-dimers more specific for fibrinolysis than the FDP test that also detects the products of the direct proteolysis of fibrinogen (fibrinogenolysis).The D-dimer test can be useful in the diagnosis of deep venous thrombosis (DVT) or pulmonary embolism (PE), two forms of venous thromboembolism (VTE). When the test is being used for this purpose, it is important that D-dimer levels are accurately measured and accurately reported because of the serious nature of this clinical decision. If the test is positive in a patient suspected to have DVT or PE, clinicians proceed with further diagnostic tests. If the test is negative, depending on the clinical situation and the sensitivity of the D-dimer assay, DVT or PE is considered unlikely and further diagnostic tests for DVT or PE might not be pursued. D-dimer is a sensitive, but not specific, diagnostic test for disseminated intravascular coagulation, and an indicator of increased risk of future myocardial infarction in patients evaluated for chest pain.

Agents in Category B are considered the second highest priority agents and are included in this group because they: Are moderately easy to disseminate Cause moderate morbidity and low mortality Require specific enhancements of Centers for Disease Control and Prevention’s (CDC) diagnostic capacity and enhanced disease surveillance

Examining the biopsy allows the structure of the marrow to be viewed as it exists in the body. It provides essential diagnostic information in conditions that disrupt the normal architecture, such as metastatic carcinoma, myelofibrosis, Hodgkin's lymphoma and granuloma. A biopsy may also be used to evaluate cellularity and identify acid-fast bacteria or fungi in less time than is needed for routine culture methods. One disadvantage of the tissue sections prepared from the biopsy sample is that morphologic detail is lost. For this reason, in many cases imprint slides or smears from the aspirated sample are also examined.

Examples of conditions in which examination of the bone marrow may provide diagnostic information include:Erythrocyte Disordersanemiamegaloblasticsideroblasticiron deficiencyerythrocytosispolycythemia veraLeukocyte DisordersneutropenialeukemialymphomaPlatelet DisordersthrombocytopeniathrombocytosisMiscellaneous Disordersprotein abnormalitiesmultiple myelomaWaldenstrom's Macroglobulinemiadiseases of the RE systemhypersplenismmetastatic carcinomagranulomatous infectionsstorage diseasesGaucher's diseaseNiemann-Pick disease

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To review, specificity is “disease focused”. The more specific a test is, the fewer false positive results will occur. Remember that a false positive result can possibly lead to a misdiagnosis with the possible consequence of unnecessary diagnostic procedures and therapies. Sensitivity, on the other hand, is “wellness or normal focused”. The more sensitive a test is, the fewer false negative results it produces.

Red cell morphology can be defined as the appearance of the erythrocytes on a Wright's stained smear.Careful examination of the red cells for the purpose of identifying abnormalities is part of the differential procedure. This examination is important because it may provide valuable diagnostic information to the physician, as well as provide a quality control mechanism to verify red cell indices values as determined by automated or manual methods.Evaluating red cell morphology involves differentiating normal morphology from abnormal and artificial morphology. The abnormal morphology covered in this unit may be seen in a variety of disorders.

Acanthocytes have 3-12 thorn-like projections irregularly spaced around the cell. Since these cells have lost their discoid shape, they are frequently smaller than normal and have little or no central pallor. Acanthocytes have an excess of cholesterol and an increased surface area. Large numbers of these cells on a smear can be of diagnostic significance. The largest percentage, 50-100% of circulating red cells, can be seen in the rare abetalipoproteinemia (hereditary acanthocytosis). Acanthocytes are easily seen as horned cells in the smear shown on the right.

Poikilocytosis is a general term used to describe variations in shape. Practically, however, this term has little meaning since cells varying in shape must be specifically identified to be of diagnostic value to the clinician.The work of the French hematologist, Marcel Bessis, with the scanning electron microscope has significantly increased our understanding of the various unusual shapes erythrocytes may assume and their associated pathophysiology.