Why D-Dimer Is the Wrong Test for Deep Vein Thrombosis

It is a vascular disease, but the vascular problem is not what is causing the pain in this elderly lady — and if medicines can manage the condition, there is no need to intervene, even if that is commercially a loss rather than a win. There has been a silent shift from a doctor-patient relationship to a doctor-hospital relationship, where a patient's data no longer stays with the treating doctor once they change hospitals. Old-school medicine — operating only when needed, never when not needed — is what should endure through that change.

Never confuse varicose veins with cellulitis and simply give a course of antibiotics to send the patient away — that is the wrongest possible thing to do, and it is not a constructed scenario. This happens regularly in real-life GP clinics, and any swollen leg deserves at least a Doppler ultrasound before it is written off as a skin infection.

Out of roughly 25 healthcare facilitators sending referrals, only one or two send a report in a structured format. A recent case arrived with mismatched patient names, ages and even genders across different files for what turned out to be the same patient — a PDF here, a broken image file there, no consolidated record. I would rather give no advice than wrong advice built on poorly collated information.

Absolutely, yes — particularly if the D-dimer is done after the acute phase, in a subacute presentation of a few days. Despite the test's high sensitivity, the result can come back in the low hundreds, nowhere near diagnostic. DVT is an anatomical problem, and for an anatomical problem the answer is to see it directly on ultrasound, not infer it from a blood marker. Vascular ultrasound is learnable within three to four months, and we train nearly all our trainees to do it routinely.

Laser ablation for superficial spider veins or one or two perforators has an excellent prognosis, and works well up to the perforator level. But if the saphenofemoral junction itself is regurgitant, open surgery to ligate the SFJ and clip the draining tributaries is usually the better option rather than relying on endovascular ablation alone.

D-dimer carries an extremely high false-positive rate. Smoking, exercise, fever or almost any infection can raise it without a DVT being present, which limits its value as a standalone diagnostic tool.

Following the Wells score, an ultrasound should be obtained within four hours of suspicion. A positive ultrasound confirms the diagnosis and anticoagulation begins immediately, without needing a D-dimer. Only when the ultrasound is negative does a positive D-dimer become useful, and even then the scan should be repeated in six to eight days.

Yes. A DVT that has been present for several days can produce a D-dimer in the low hundreds, well below the diagnostic threshold, despite the test's high sensitivity in the acute phase.

Yes. Any imaging done for DVT should be completed with a CT pulmonary angiogram, since deep vein thrombosis and pulmonary embolism sit on the same spectrum of venous thromboembolism.