33. Choice and discussion of laboratory parameters in hemorrhagic diathesis.

Choice and discussion of laboratory parameters in hemorrhagic diathesis.

Haemorrhagic diathesis - is an unusual susceptibility to bleed (hemorrhage) mostly due to hypocoagulability, in turn caused by a coagulopathy (a defect in the system of coagulation). Several types are distinguished, ranging from mild to lethal.

Hemorrhagic diathesis

Vascular abnormalities – inborn, acquired

Platelet - associated: thrombopenia and thrombopathia

Plasma factors – associated:

1. а) inheritted (only 1 factor) Afibrinogenemia, Deficiency of f. XI, f. XIII.
2. б) acquired (several factors at once):•Liver diseases: •Deficiency of vit. K: •DIC*: •Hyperfibrinolysis •Amyloidosis

Excessive bleeding can result from:

1. (1) increased fragility of vessels
2. (2) platelet deficiency or dysfunction
3. (3) derangement of coagulation
4. (4) combinations of these

The normal hemostatic response involves the blood vessel wall, the platelets, and the clotting cascade. Tests used to evaluate different aspects of hemostasis are the following:

1. Bleeding time. This measures the time taken for a standardized skin puncture to stop bleeding and provides an in vivo assessment of platelet response to limited vascular injury. The reference range depends on the actual method employed and varies from 2 to 9 minutes. Prolongation generally indicates a defect in platelet numbers or function. Bleeding time test is fraught with variability and poor reproducibility.
2. Hence new instrument-based assay systems such as platelet function analyzer-100 (PFA-100) that provide a quantitative measure of platelet function under conditions of high shear stress are being evaluated as replacements for the bleeding time test.
3. Prothrombin time (PT). This assay tests the extrinsic and common coagulation pathways. The clotting of plasma after addition of an exogenous source of tissue thromboplastin (e.g., brain extract) and Ca2+ ions is measured in seconds. A prolonged PT can result from deficiency or dysfunction of factor V, factor VII, factor X, prothrombin, or fibrinogen. Reference ranges: 11-13s, or 70-120%
4. Partial thromboplastin time (PTT). This assay tests the intrinsic and common clotting pathways. The clotting of plasma after addition of kaolin, cephalin, and calcium ions is measured in seconds. Kaolin serves to activate the contact-dependent factor XII, and cephalin substitutes for platelet phospholipids. Prolongation of the PTT can be due to deficiency or dysfunction of factor V, VIII, IX, X, XI, or XII, prothrombin, or fibrinogen. Reference values for PTT vary among laboratories, but generally range between 25 and 38 seconds.