D-dimer test

Which sample is needed for the D-dimer test?

1. Citrate plasma is needed.
2. It is stable for 8 hours at room temperature. It can be kept at -20 °C for 6 months.

What are the indications for the D-Dimer test?

1. This test is done to diagnose DIC (disseminated intravascular coagulopathy).
2. It monitors the DIC or hypercoagulable states.
3. It can diagnose other thromboembolic disorders (venous thrombosis).
4. It can diagnose Pulmonary embolism.
5. For the diagnosis of acute myocardial infarction.
   1. D-dimer may be increased by atrial fibrillation, congestive heart failure, and cirrhosis.
6. It monitors anticoagulant therapy.

What is the definition of D-dimer?

1. D-dimer is a fibrin degradation product (FDP) by fibrinolysis.
2. Plasmin action on cross-linked fibrin clots produces d-dimers.
3. The presence of D-dimer confirms that both thrombin and plasmin have been generated.
4. Factor XIII generates a D-dimer by covalently linking the D regions of the fibrin molecule.
5. D-dimer assesses both thrombin and plasmin activity.
6. Damaged blood vessels and exposure to collagen activate both the intrinsic and extrinsic coagulation cascades.
   1. SO D-dimer is a fibrin degradation product (fragment).
   2. It is found in the blood as a small protein fragment after fibrin clot degradation (fibrinolysis).
   3. It consists of 2 D-fragments of the fibrin protein, joined by a cross-link, forming a protein dimer.

What are the S/S of disseminated intravascular coagulopathy (DIC)?

1. The patient may have weakness and malaise.
2. The main feature is bleeding, especially from the venipuncture site or a recent injury.
3. There may be bleeding in the gastrointestinal tract. Oropharynx, into the lungs, and in the urogenital tract.
4. During delivery, vaginal bleeding may be very severe.
5. Acrocyanosis is characterized by irregularly shaped cyanotic patches.
6. Microthrombi may cause skin lesions.
   1. There may be gangrene of the finger or toes.
7. There may be occult bleeding to massive GIT bleeding.
   1. There is abdominal distension.
8. Patients may develop renal failure.
   1. There may be hematuria.
   2. There is oliguria.
9. Patients may have cerebral ischemia.
   1. There may be subarachnoid hemorrhage.
   2. There is a slight confusion about convulsions and coma.
10. These patients have respiratory symptoms like:
    1. Cyanosis.
    2. Hypoxemia.
    3. Adult respiratory distress syndrome (ARDS).
    4. Tachypnea.
    5. Pulmonary infarction.
11. Some patients with mucin-producing adenocarcinoma may develop subacute or chronic DIC.

What are the complications of Disseminated Intravascular Coagulopathy (DIC)?

1. Thrombotic conditions such as deep vein thrombosis, sickle cell anemia, pulmonary embolism, and malignancy-related thrombosis are associated with elevated D-dimer levels.
2. FDP and D-dimer form as a complication of disseminated intravascular coagulopathy (DIC).

How do you determine the Diagnosis of Disseminated Intravascular Coagulopathy (DIC)?

1. Fibrinogen concentration is low.
2. Platelets are low.
3. Thrombin time is prolonged.
4. Fibrinogen degradation products (FDP) and D-dimer are elevated and detected in urine and serum.
5. PT and APTT are prolonged in the acute phase.
6. The D-dimer test detects the cross-linked fibrin degradation products.
7. The D-dimer assay is more specific than the FDP assay.
8. D-dimer is a highly specific marker of fibrin degradation products.
9. Combining the positive FDP and D-dimer tests is highly specific and sensitive for diagnosing DIC.
10. A positive D-dimer result is evidence of DIC or other causes of intravascular thrombosis.
11. D-dimer can be used as a screening test for deep vein thrombosis (DVT).
12. The concentration of fibrin breakdown products will increase when fresh venous thrombosis occurs.
13. A negative result is useful in the emergency department for excluding DVT in clinically suspected patients.

What is the advantage of D-dimer?

1. There is no interference from fibrinogen, so the test can be performed on plasma without the need to collect it in a special tube.

What are the disadvantages of D-dimer?

1. It has limited usefulness because it is used in fibrinolysis and will not detect fibrinogen breakdown products.
2. Elevated D-dimer levels have limited value in cancer, post-surgical inflammation, or trauma, limiting their usefulness.

How will you classify Disseminated Intravascular Coagulopathy (DIC) on various factors?

What are the Normal values of D-dimer?

Source 1

• Negative
• <0.25 mg/L

Source 2

• Normal = negative ( no D-dimer fragments are seen).
• <250 ng/mL (<250 µg/L).

Source 4

• Normally, plasma D-dimer levels are negative.
• Qualitative: It is negative
• Quantitative : < 250 ng/mL or < 250  µg/L ( SI unit)
• Critical value >40 mg/L (40 µg/mL).

Source 6

• <0.4 mcg/mL

What factors will lead to a False-positive test?

1. This is seen in heparin therapy.
2. The Rheumatoid factor can yield falsely elevated FDP values.
3. This test is positive in patients after surgery or trauma.
4. The false-positive test is seen in estrogen therapy and pregnancy.

What are the causes of increased levels of D-dimer?

1. Primary and secondary fibrinolysis.
2. DIC
3. Thrombolytic therapy.
4. Deep vein thrombosis.
5. Pulmonary embolism.
6. Arterial thromboembolism.
7. Vaso-occlusive crises of sickle cell anemia.
8. Pregnancy (Especially the postpartum period).
9. Malignancy.
10. Surgery.

Questions and answers:

• Please see more details in the fibrinogen degradation products FDP.