D-dimer
D-dimer (or D dimer) is a fibrin degradation product (or FDP), a small protein fragment present in the blood after a blood clot is degraded by fibrinolysis.
It is so named because it contains two crosslinked D fragments of the fibrin protein.
D-dimer concentration may be determined by a blood test to help diagnose thrombosis.
Since its introduction in the 1990s, it has become an important test performed in patients with suspected thrombotic disorders. While a negative result practically rules out thrombosis, a positive result can indicate thrombosis but does not rule out other potential causes.
Its main use, therefore, is to exclude thromboembolic disease where the probability is low.
In addition, it is used in the diagnosis of the blood disorder disseminated intravascular coagulation.
Indications
D-dimer testing is of clinical use when there is a suspicion of
deep venous thrombosis (DVT),
pulmonary embolism (PE) or
disseminated intravascular coagulation (DIC).
It is under investigation in the diagnosis of aortic dissection.
For DVT and PE, there are possible various scoring systems that are used to determine the a priori clinical probability of these diseases; the best-known is the Wells score.
For a very high score, or pretest probability, a D-dimer will make little difference and anticoagulant therapy will be initiated regardless of test results, and additional testing for DVT or pulmonary embolism may be performed.
For a moderate or low score, or pretest probability:
A negative D-dimer test will virtually rule out thromboembolism:
the degree to which the D-dimer reduces the probability of thrombotic disease is dependent on the test properties of the specific test used in the clinical setting:
most available D-dimer tests with a negative result will reduce the probability of thromboembolic disease to less than 1% if the pretest probability is less than 15-20%.
Chest CT angiography should not be used to evaluate pulmonary embolism for persons with negative results of a D-dimer assay.
If the D-dimer reads high, then further testing (ultrasound of the leg veins or lung scintigraphy or CT scanning) is required to confirm the presence of thrombus.
Anticoagulant therapy may be started at this point or withheld until further tests confirm the diagnosis, depending on the clinical situation.
In some hospitals, they are measured by laboratories after a form is completed showing the probability score and only if the probability score is low or intermediate. This reduces the need for unnecessary tests in those who are high-probability.
Performing the D-dimer test first can avoid a significant proportion of imaging tests and is less invasive. Since the D-dimer can exclude the need for imaging, specialty professional organizations recommend that physicians use D-dimer testing as an initial diagnostic.
Interpretation
Thrombotic diseases
Various kits have a 93-95% sensitivity (true positive rate).
For hospitalized patients, one study found the specificity to be about 50% (true negative rate) in the diagnosis of thrombotic disease.
False positive readings can be due to various causes:
liver disease, high rheumatoid factor,
inflammation,
malignancy,
trauma,
pregnancy,
recent surgery
as well as advanced age.
False negative readings can occur if the sample is taken either too early after thrombus formation or if testing is delayed for several days. Additionally, the presence of anti-coagulation can render the test negative because it prevents thrombus extension.False values may be obtained if the specimen collection tube is not sufficiently filled (false low value if underfilled and false high value if overfilled). This is due to the dilutional effect of the anticoagulant (the blood must be collected in a 9:1 blood to anticoagulant ratio).Likelihood ratios are derived from sensitivity and specificity to adjust pretest probability.
In interpretation of the d-dimer, for patients over age 50 a value of ageX10 may be abnormal.
Interpretation:
Unit mg/L
Or ug/ml
D-dimer (or D dimer) is a fibrin degradation product (or FDP), a small protein fragment present in the blood after a blood clot is degraded by fibrinolysis.
It is so named because it contains two crosslinked D fragments of the fibrin protein.
D-dimer concentration may be determined by a blood test to help diagnose thrombosis.
Since its introduction in the 1990s, it has become an important test performed in patients with suspected thrombotic disorders. While a negative result practically rules out thrombosis, a positive result can indicate thrombosis but does not rule out other potential causes.
Its main use, therefore, is to exclude thromboembolic disease where the probability is low.
In addition, it is used in the diagnosis of the blood disorder disseminated intravascular coagulation.
Indications
D-dimer testing is of clinical use when there is a suspicion of
deep venous thrombosis (DVT),
pulmonary embolism (PE) or
disseminated intravascular coagulation (DIC).
It is under investigation in the diagnosis of aortic dissection.
For DVT and PE, there are possible various scoring systems that are used to determine the a priori clinical probability of these diseases; the best-known is the Wells score.
For a very high score, or pretest probability, a D-dimer will make little difference and anticoagulant therapy will be initiated regardless of test results, and additional testing for DVT or pulmonary embolism may be performed.
For a moderate or low score, or pretest probability:
A negative D-dimer test will virtually rule out thromboembolism:
the degree to which the D-dimer reduces the probability of thrombotic disease is dependent on the test properties of the specific test used in the clinical setting:
most available D-dimer tests with a negative result will reduce the probability of thromboembolic disease to less than 1% if the pretest probability is less than 15-20%.
Chest CT angiography should not be used to evaluate pulmonary embolism for persons with negative results of a D-dimer assay.
If the D-dimer reads high, then further testing (ultrasound of the leg veins or lung scintigraphy or CT scanning) is required to confirm the presence of thrombus.
Anticoagulant therapy may be started at this point or withheld until further tests confirm the diagnosis, depending on the clinical situation.
In some hospitals, they are measured by laboratories after a form is completed showing the probability score and only if the probability score is low or intermediate. This reduces the need for unnecessary tests in those who are high-probability.
Performing the D-dimer test first can avoid a significant proportion of imaging tests and is less invasive. Since the D-dimer can exclude the need for imaging, specialty professional organizations recommend that physicians use D-dimer testing as an initial diagnostic.
Interpretation
Thrombotic diseases
Various kits have a 93-95% sensitivity (true positive rate).
For hospitalized patients, one study found the specificity to be about 50% (true negative rate) in the diagnosis of thrombotic disease.
False positive readings can be due to various causes:
liver disease, high rheumatoid factor,
inflammation,
malignancy,
trauma,
pregnancy,
recent surgery
as well as advanced age.
False negative readings can occur if the sample is taken either too early after thrombus formation or if testing is delayed for several days. Additionally, the presence of anti-coagulation can render the test negative because it prevents thrombus extension.False values may be obtained if the specimen collection tube is not sufficiently filled (false low value if underfilled and false high value if overfilled). This is due to the dilutional effect of the anticoagulant (the blood must be collected in a 9:1 blood to anticoagulant ratio).Likelihood ratios are derived from sensitivity and specificity to adjust pretest probability.
In interpretation of the d-dimer, for patients over age 50 a value of ageX10 may be abnormal.
Interpretation:
Unit mg/L
Or ug/ml
