D
D-dimer and fibrin/fibrinogen degradation products
Also called: (FDP); Fibrin/Fibrinogen Breakdown Product (FBP)
Purpose of the test
The D-dimer test and the fibrin degradation products are tests that help determine whether a clot is present in the diagnosis of deep vein thrombosis, disseminated intravascular coagulation (DIC), or an acute myocardial infarction. They are also used in the diagnosis of hypercoagulable conditions that cause recurrent thrombosis.
Basics the nurse needs to know
In fibrinolysis, D-dimers are fragments of fibrin that appear in the blood when a thrombus (clot) dissolves or degrades. Fibrin degradation products are end products of the dissolving fibrin and fibrinogen.
These tests are used for screening to exclude the presence of a deep vein thrombus. When the results are in the normal range or negative, no thrombus is present. Elevated test results or the presence of D-dimer fragments is evidence that thrombus formation occurred and lysis of the thrombus is occurring. When the value is elevated, additional tests are needed to determine a specific diagnosis. The combination of elevated levels of fibrin/fibrinogen degradation products and D-dimer fragments is highly predictive of DIC. In DIC, the fibrin/fibrinogen degradation products value rises to greater than 40 μg/mL (SI: >40 mg/L).
Disseminated intravascular coagulation (DIC) screen
D-dimer and fibrin/fibrinogen degradation products are part of the panel of tests to assess for DIC. The additional tests in this group include Prothrombin Time (see p. 525), Activated Partial Thromboplastin Time (see p. 42), Platelet Count (see p. 499), and Fibrinogen (see p. 315). DIC is a common and often severe coagulation disorder commonly precipitated by sepsis, severe tissue injury, or some complications of pregnancy. When the anticoagulation and fibrinolytic systems are overwhelmed by the underlying disorder, DIC can result. In DIC, the patient develops systemic microvascular thrombi and, as platelets and natural anticoagulant factors are depleted, the patient begins to bleed.
In laboratory testing, DIC causes the values of D-dimer and fibrin/fibrinogen degradation products to be elevated as a result of the lysis of the clot or clots. The loss of platelets and anticoagulants result in a prolonged prothrombin time and activated partial thromboplastin time. There is a decrease in the platelet count and fibrinogen value.
Interfering factors
NURSING CARE
Nursing actions are similar to those used in other venipuncture procedures (see Chapter 2), with the following additional measures.
Posttest
Dexamethasone suppression test
Purpose of the test
The dexamethasone suppression test assesses the hypothalamic-pituitary-adrenal axis. It usually is performed to identify Cushing’s syndrome. With the dexamethasone test, Cushing’s disease and ectopic production of adrenocorticotropic hormone (ACTH) and adrenal tumors can be differentiated.
Basics the nurse needs to know
Dexamethasone (Decadron) is a potent glucocorticoid. It will normally suppress ACTH secretion by the pituitary gland via the normal hormonal feedback mechanism. With the suppression of ACTH, the stimulation for cortisol secretion is suppressed in the adrenal cortex, resulting in a decrease in plasma cortisol and urinary corticosteroid levels.
High-dose dexamethasone testing can be helpful in distinguishing Cushing’s disease (pituitary hypersecretion of ACTH) from adrenal tumors or ectopic secretion of ACTH. With high-dose dexamethasone, pituitary secretion of ACTH can be suppressed, with a resulting decrease in plasma cortisol levels. No change will occur with adrenal tumors or ectopic ACTH production.
How the test is done
A variety of dexamethasone procedures are possible. Low-dose dexamethasone testing may be carried out overnight or over 2 days. Overnight testing requires the oral administration of dexamethasone at night (10 pm to 11 pm). The next morning, a plasma cortisol level is determined. With the 2-day method, dexamethasone is given orally every 6 hours for 2 days. A 24-hour urine specimen is obtained before and after administration (see discussion of 17-Hydroxycorticosteriods, p. 389), and a plasma cortisol test is performed 6 hours after the last dose of dexamethasone.
High-dose dexamethasone testing begins with obtaining a baseline plasma cortisol level, then giving dexamethasone orally at night, and obtaining another plasma cortisol level the next morning.
Interfering factors
NURSING CARE
Nursing actions are similar to those used in other venipuncture and urine collection procedures (see Chapter 2). Also, review discussions of 17-Hydroxycorticosteroids (p. 389), Free Cortisol (p. 319), and Cortisol, Total (p. 227).
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