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Lab Manual for Moffitt-Long and Mount Zion

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Fibrin D-Dimers

Item Value
Approval req'd? No
Available Stat? Yes
Test code FDD
Performed by Parnassus Hematology
In House Availability 24 hours, 7 days per week
Method Immunoturbimetric (Liatest)
Collection Instructions Blue top filled to full extent of vacuum
Container type 3.2% sodium citrate, Blue top tube
Amount to Collect 2.7 mL
Sample type Citrated plasma
Preferred volume 1.0 mL plasma
Min. Volume 0.5 mL plasma
UCSF Rejection Criteria Lipemic or turbid samples
Processing notes Deliver specimen immediately to Hematology
Units ng/mL FEU
Normal range <400 ng/mL
Synonyms FDD; Fibrin D-Dimers
Stability Room temperature 4 hours
Turn around times 1 hour
Additional information Reference Interval
The fibrin D-dimer (FDD) levels in 113 normal blood donors were used to calculate a reference interval using a transformed parametric method. This analysis yielded an upper limit of normal of 664 ng/mL with approximately 12% of FDD values >400 ng/mL (1). In APeX, the upper limit of normal has been set at 400 ng/mL in order to alert clinicians to the cutoff value for exclusion of venous thromboembolism (VTE; see below).

Evaluation for VTE, including pulmonary embolism (PE)
In patients at a low-to-intermediate clinical probability for PE and for whom imaging studies are under consideration, an FDD <400 ng/mL may permit diagnostic imaging (e.g., helical contrast computed tomography or ventilation/perfusion scan) to be avoided. Clinical correlation is advised in these settings. The FDD should only be ordered when there is reasonably substantive clinical suspicion for VTE/PE, as an elevated FDD is a nonspecific finding and can be elevated in the setting of recent fibrinolytic therapy, recent trauma or surgery, large hematoma, malignancy, sepsis or severe infection, cirrhosis, pregnancy, atherosclerosis, hemoglobinopathy, and age >60 years.

Some settings in which the FDD may not be appropriate to exclude VTE/PE include (2):
1. Children
2. High probability for VTE/PE by clinical criteria
3. Current anticoagulation therapy
4. Suspected upper extremity thrombosis or thrombosis distal to knee
5. Substantial time elapsed between onset of thrombosis and laboratory testing (FDD has a half-life of approximately 7 hours and may be cleared from circulation following thrombosis)
6. Deficiency of fibrinolytic enzymes

Evaluation for disseminated intravascular coagulation (DIC)
Obtain a current prothrombin time (PT), activated partial thromboplastin time (aPTT), platelet count, and fibrinogen prior to ordering FDD. In an appropriate clinical context, an FDD >8200 ng/mL is suggestive of DIC. Serial studies following the demonstration of a positive result are not generally useful.

Ordering interval
An acceptable ordering interval for the FDD is (1) 48 hours after last FDD or (2) 24-48 hours after last FDD with the most recent result <6000 ng/mL. If neither of these criteria are met, the FDD will be automatically canceled. Please contact the Hematology Lab Medicine Resident at 353-1747 if the clinical situation warrants more frequent re-evaluation of the FDD.

Limitations
· Cloudy specimens (e.g., lipemic specimens) may yield artifactually low values. In some cases, such specimens cannot yield interpretable results.
· The presence of rheumatoid factor at a level greater than 50 IU/mL may lead to an over-estimation of the FDD.

References
1. UCSF in-house studies, 2004 and 2009.
2. Clinical Laboratory Standard Institute (CLSI). Document H59-A: Quantitative D-Dimer for the Exclusion of Venous Thromboembolic Disease. Approved Guideline.
CPT coding 8537
LOINC code 48065-7
Last Updated 1/15/2014 10:30:08 AM
Entry Number 1289

If you have additional questions regarding this test, please call: 415-353-1667

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