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Terms in this set (128)

-SILENT CARRIER STATE ( ___, alpha / alpha, alpha): Characterized by deletion of a single alpha-globin gene and barely detectable reduction in alpha-globin chain synthesis. Because these individuals have three normal genes, they are completely asymptomatic and do not have anemia.
-ALPHA THAL TRAIT ( ____, _____ / alpha, alpha) or ( ____ , alpha / ____ , alpha): Characterized by deletion of two alpha-globin with both deletions occurring on the same chromosome ( ___ , ___ / alpha, alpha) or one deletion occurring on each chromosome 16 ( ___ , alpha / ___ , alpha). Both genetic patterns produce similar, mild deficiencies in alpha chain synthesis and are therefore clinically identical with minimal anemia and no abnormal physical signs.
-HEMOGLOBIN H DISEASE ( ___ , ___ / ___ , alpha): Associated with the deletion of three of the four alpha genes and mainly seen in in Asian populations. Synthesis of alpha chains markedly reduced with excess beta chains forming tetramers called hemoglobin H (HgH). HgH may be oxidized and visualized as red cell inclusions in peripheral blood smears. Because HgH is unable to withstand oxidative stress, it forms precipitates in the red cell which are then removed by the spleen resulting in a moderately severe anemia.
-HYDROPS FETALIS ( ___ , ___ / ___ , ___ ): Most severe form resulting from deletion of all four alpha-globin genes. In the fetus, excess gamma chains (HgF chains) form tetramers called hemoglobin Bart's (HgB). HgB has extremely high oxygen affinity and is therefore unable to deliver O2 to tissues with severe anoxia resulting in intrauterine fetal death.
This test screens for abnormalities in the reactions of primary hemostasis (formation of the platelet plug). This is mostly independent of the plasma coagulation reactions (secondary hemostasis). While a blood pressure cuff is maintained at 40 mmHg, a standardized incision is made in the forearm. The excess blood is gently blotted away, and the time to cessation of blood flow is recorded. This is a very crude test, which is subject to many variables - contributed by both the technologist and the patient. This is also one of the most misused (abused) and misunderstood tests that the laboratory offers. In particular, it is frequently (mis)used to predict the potential for bleeding in a patient about to undergo surgery or an invasive procedure. There is a large body of literature which does not support the use of the bleeding time in this clinical setting. The best predictor of whether a patient will suffer excessive bleeding during a procedure, is an adequate patient HISTORY! In a patient with no personal or family history of excessive bleeding, the BT is close to worthless as a predictor of such an event. This is a classic example of applying a SCREENING test to the GENERAL population, as opposed to a SELECTED population, such as those with a positive bleeding history. In the former, this test loses its predictive value.
The following are amongst the more accepted uses of the bleeding time:
-As part of the evaluation of a patient with a SUSPECTED bleeding disorder.
-Evaluating the response to therapy - DDAVP in vWD, dialysis in a uremic patient.