D-Dimers

Notes

In accordance with Trust Guidelines, D-Dimers will only be performed in the following instances:

• Low or Intermediate (Wells score) probability DVT
• Low (Wells score) probability PE
• Investigation of Disseminated Intravascular Coagulation (DIC)
• Any other reason for testing must be discussed with the laboratory prior to requesting the test.

Information on how to perform a probability (Wells) score for suspected DVTs and PEs can be found on the Trust's NHS SharePoint site. (Please note, access is currently only available to Trust users). Please search for action cards A2099 VTD1 (Diagnosis of Deep Vein Thrombosis) and A2099 VTD2 (Management of Pulmonary Embolism).

Please clearly state the reason for the D-Dimer request, and the associated probability score, on the request form. Without this information, the test will not be performed. Also, if requesting as an add-on test through email, the request must also be telephoned through to the laboratory.

• Test performed at CGH and GRH

Sample requirements

2ml, 3ml or 3.5ml Trisodium Citrate tube

Turnaround Times

• Clinical emergency: 30 mins
• Other urgent requests: 60 mins
• Routine: within 2 hours

Reference Ranges

If D-dimers are used in conjunction with clinical scoring:

For DVT: <500ng/ml: Negative

>500ng/ml:Positive

For PE: Consider following Trust guidance on age related D Dimers:

Patient aged <50: >500ng/ml: Positive

Patient aged >50: >(Age x 10)ng/ml: Positive

Interfering substances

Interfering substances include high levels of lipaemia, haemolysis and bilirubin.

Poor quality samples which are under or overfilled can also lead to errorneous results, so will not be tested.

Add ons

Ideally within 4 hours, although the test can be added on up to 24 hours from when the sample was initially taken.