Why do we do so many d-dimers?
I work in an Urgent care centre and a common complaint we see is swollen lower legs. Personally I think we do way too many d-dimer tests to help exclude Deep vein thrombosis (DVT) as a differential diagnosis when there are many other causes we should consider.
A DVT is the formation of a blood clot in a deep vein, usually in the legs, which partially or completely obstructs blood flow back to the heart.
Localised causes of lower leg swelling can include:
Trauma such as a gastrocnemius tear or fracture-could be a stress fracture or traumatic
Chronic venous insufficiency and lipodermatosclerosis (a chronic inflammatory condition characterised by subcutaneous fibrosis and hardening of the skin on the lower legs)
Cellulitis or Osteomyelitis infections
Allergic reaction
Bakers cyst rupture
Rheumatoid arthritis or other inflammatory arthritis diseases
Lymphoedema
Congenital malformations such as arteriovenous fistula
Malignancy of bone or muscle
Dependant oedema due to stasis, poor mobility, obesity and dependancy.
Superficial thrombophlebitis
Deep vein thrombosis
Systemic causes of lower leg swelling include:
Congestive Cardiac Failure
Hyponatremia
Liver failure
Nephrotic syndrome
Acute kidney injury and Chronic Kidney disease
Fluid overload
Anaemia
Medication such as NSAIDS and calcium antagonists
Hypothyroidism
Hereditary angioneurotic oedema
Obstructive sleep apnoea
So how do we decide which one it is?
The consultation or ‘history take’ will establish the nature of the presentation and give you vital clues as to which one of these diagnosis is the correct one.
Important factors to establish during the consultation:
Is it acute or chronic
Unilateral or bilateral
How fast did it take for the swelling to develop
Painful or not painful
Any fever
Where do they sleep at night? In a chair on on their bed
Baseline mobility
Are there any associated symptoms such as shortness of breath, chest pain etc.
Any history of previous DVT
Any history of cancer or weight loss
Any history of peripheral vascular disease or intermittent claudication
History of Intravenous drug use
History of coagulation problems
Drug history
Recent fracture or long distance traveling/immobility
A typical DVT history is acute unilateral leg swelling (very rare in both legs). Often described as a throbbing sensation usually in the thigh or calf worse when standing or walking. The skin often goes red and warm and veins become more prominent. This can be hard to see on darker skin tones.
Risk factors of DVT to consider:
A history of DVT.
Cancer (known or undiagnosed).
Age over 60 years.
Being overweight or obese.
Male sex.
Heart failure.
Acquired or familial thrombophilia.
Inflammatory disorders (for example, vasculitis, inflammatory bowel disease).
Risk factors that temporarily increase the likelihood of DVT include:
Significant immobility.
Significant trauma or direct trauma to a vein (for example, intravenous catheter).
Hormone treatment (for example hormone replacement therapy).
Pregnancy and the postpartum period.
Dehydration.
The Examination of the patient:
Look for swelling or pitting oedema. Measure both calves and see if there is a difference of more than 2cm.
Check for tenderness along the deep vein distribution most found at the back of the leg not the front. The seven deep veins in the leg are: Popliteal, Peroneal, Profunda Femoris, Common femoral, femoral, anterior tibial and posterio tibial.
Look for changes in skin colour.
Look for raised/prominent veins or worsening varicose veins
Feel the difference in temperature to both legs. Cold peripherally and pale is a bad sign and you may be looking at an ischaemic limb. A DVT will often cause it to be hot. Try raising the leg up and if this causes it to go pale and lowering brings colour back this could also be due to an arterial blockage.
Check for pulses on both legs at femoral, popliteal, posterior tibial, dorsalis pedis. If in doubt use a doppler scanner.
Risk assessment tools:
The WELLS Score for DVT is an excellent tool used by clinicians to assess the possibility of a DVT. If the WELLS score is high it means it is more likely to be a clot but only if the history suggests DVT!
However, in order to use this tool a good history take and examination should be done and should suggest to the physician that DVT is a diagnostic possibility. It also reccomends never to do the d-dimer before a good history and clinical assessment has been done because it can lead you entirely down the wrong path.
Investigations:
A d-dimer blood test is a protein fragment that is created when a blood clot dissolves in you body. This blood test has a high sensitivity but low specificity for detecting venous thromboembolisms. It can often come back raised for many other reasons such as inflammatory conditions, pregnancy, recent surgery, obesity and heavy smoking. This is why it is essential that you actually suspect a DVT before doing this test to avoid expensive unnecessary investigations and potentially hazardous drugs to be administered to the patient, which could actually do them harm.
A venous doppler Ultrasound scan is the only way to truly be sure that there is no deep vein thrombosis present. A systematic review and meta-analysis done by Goodacre et al (2005) found that the specificity and sensitivity of this examination was approximately 94% which is excellent and the technology used has advanced considerably in the last 17 years so I’m sure it will be even higher now.
Treatment of DVT
Often treatment depends on your local policy and Hematology advice but is always anticoagulation of some form. The duration depends on the cause. If no cause is found then further investigations should be arranged by the Haemostasis Multi-disiplinary team to check for haematological causes or even an undiagnosed malignancy.
Patients with significant renal failure, or morbidly obese can be difficuilt to manage and often require renal/haematology specialist input.
Remember to establish the risk of bleeding if starting a new anticoagulant. This can be done by using the HAS-BLED score and if the risk is medium to high then speak to a specialist before making any decisions to protect yourself!
I hope you found this useful and as always I am happy to hear about your experiences so we can all learn from each other and become better clinicians.
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