Suspected deep vein thrombosis

NICE NG158; NICE QS201

Compression ultrasound answers this question completely, immediately and with nothing injected. Almost every vetting decision is either a redirection away from cross-sectional imaging, or a timing question about how quickly the scan is needed given the Wells score and whether interim anticoagulation has been given.

A unilaterally swollen, painful or erythematous limb, with or without a raised D-dimer, in a patient whose clinical probability score makes imaging appropriate.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Pre-test probability

Which validated rule the referrer applied, and what it gave. Each of these is also a calculator here.

D-dimer

Whether it was done at all is as informative as the value.

Anticoagulated or on antiplatelets

Moves the threshold for imaging head injury further than any other single item of history.

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

Venous duplex ultrasound for deep vein thrombosis

Ultrasound venous Doppler (limb)

What we'd amend, and why

A normal vein collapses completely under gentle probe pressure because it is a thin-walled, low-pressure tube; a vein containing thrombus does not. That single mechanical observation is the diagnosis, and it works whether the clot is fresh and anechoic or old and echogenic — which matters, because acute thrombus is often invisible on greyscale alone. Colour and spectral Doppler are supporting evidence rather than the test: loss of respiratory phasicity in the common femoral vein is the indirect sign that points to an obstruction higher in the pelvis, where the probe cannot compress.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayadult — Adults

Decision support only. Local protocol takes precedence.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

DVT unlikely by Wells with a negative D-dimer

Role	Study & protocol	Why this answers the question
First line	Ultrasound venous Doppler (limb) Venous duplex ultrasound for deep vein thrombosis usually not appropriate	The pathway has already answered this. A two-level Wells score in the unlikely band together with a D-dimer below the threshold carries a negative predictive value high enough to stop, and NG158 stops there — the correct next move is to consider the alternative diagnoses that produce the same leg, which are ruptured Baker's cyst, cellulitis, calf haematoma, chronic venous insufficiency and lymphoedema. Scanning anyway is not neutral: it consumes an urgent vascular laboratory slot that a likely-score patient is waiting for, and it finds the isolated distal or chronic organised thrombus that then generates an anticoagulation decision nobody needed to make. Three cautions. The exclusion needs both halves — a negative D-dimer at a LIKELY score excludes nothing and the scan must go ahead. The D-dimer must be a current one from this episode, read against the laboratory's own threshold. And if symptoms progress, the score changes and the question reopens; this is a verdict about today, not a permanent one.

This arm is entered only when the referrer states both facts. A request that gives neither is not a low-probability request — it is an unscored one, and it resolves on the default pathway exactly as it always did.
Pregnancy, the puerperium, recent surgery, active malignancy and advanced age all raise the D-dimer independently. The first of those is excluded from this fork outright; for the others the score is what protects the patient, which is why the low band is required rather than the D-dimer alone.

Anticoagulation already started — the same scan, on a different clock

Role	Study & protocol	Why this answers the question
First line	Ultrasound venous Doppler (limb) Venous duplex ultrasound for deep vein thrombosis usually appropriate	Anticoagulation on this card is a clock, not a cancellation. NG158 asks for a proximal leg vein ultrasound with the result available within about four hours of a likely Wells score; where the service cannot deliver that, interim therapeutic anticoagulation covers the interval and the scan target becomes twenty-four hours. That is the entire effect — the study, the protocol and the segments examined are identical, and the substitution only works if the scan actually follows, because a patient anticoagulated on a suspicion nobody went on to confirm or refute has been half-treated indefinitely. The request has to say which anticoagulation it means, because the two readings pull in opposite directions. Interim cover started today for this leg is what buys the twenty-four hour window. A patient already on therapeutic anticoagulation for another reason — atrial fibrillation, a previous event — buys nothing by it: thrombus forming through established therapeutic anticoagulation is treatment failure rather than reassurance, it argues for the earlier slot rather than the later one, and it puts recurrence against residual chronic thrombus at the centre of the report, which is what makes retrieving the previous study before scanning worth the few minutes it takes.
Problem solving	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase	Unchanged by the anticoagulation, and worth keeping on the ladder here because this is the group in which it is most often needed: thrombus above the inguinal ligament in the iliac veins or inferior vena cava cannot be compressed by a probe and is often only inferred from a flat common femoral waveform. A delayed venous-phase acquisition opacifies those veins and shows the pelvic mass, nodal disease or compression that explains why they thrombosed. It is a second study after an ultrasound, not an alternative to one.

Nothing in this fork defers anything on its own account. The twenty-four hour window exists because an interim dose has covered the interval; it is a wider target, not a lower priority, and it closes.
Where the anticoagulation predates the leg, read this fork as a prompt rather than as reassurance. State the drug, the indication and how long it has run, because that is what separates a first event from a failure of treatment — and it is what the previous ultrasound has to be read against.

Adults

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	Ultrasound venous Doppler (limb) Venous duplex ultrasound for deep vein thrombosis usually appropriate	A normal vein collapses completely under gentle probe pressure because it is a thin-walled, low-pressure tube; a vein containing thrombus does not. That single mechanical observation is the diagnosis, and it works whether the clot is fresh and anechoic or old and echogenic — which matters, because acute thrombus is often invisible on greyscale alone. Colour and spectral Doppler are supporting evidence rather than the test: loss of respiratory phasicity in the common femoral vein is the indirect sign that points to an obstruction higher in the pelvis, where the probe cannot compress.
Problem solving	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase	The one situation where cross-sectional imaging genuinely adds something: thrombus above the inguinal ligament in the iliac veins or inferior vena cava, which cannot be compressed by a probe and is often only inferred from an abnormal common femoral waveform. A delayed venous-phase acquisition opacifies these veins and also shows the pelvic mass, nodal disease or compression that explains why they thrombosed. It is a second study after an ultrasound, not an alternative to one.

Pitfalls

Requesting CT for a swollen calf. It is more radiation, an injection, and a less sensitive test than the one that should have been booked.
Reporting a negative proximal study without stating whether the calf was examined, which leaves the referrer unable to decide about a repeat scan.
Calling chronic organised thrombus a new event. Vein diameter, wall thickening, echogenicity and collateral formation all help, but the previous study helps most.
Failing to look above the inguinal ligament when the whole leg is swollen and the common femoral waveform is flat — isolated iliac thrombosis is missed by a standard proximal examination.
Treating a negative scan as excluding venous thromboembolism when the presentation was breathlessness rather than a swollen leg. Those are different questions and a negative leg study does not answer the chest one.
Escalating a pregnant patient to pelvic CT. Compression ultrasound is the first study in pregnancy exactly as it is outside it, and this is the group in whom isolated iliac thrombosis is commonest — whole-leg swelling with buttock or back pain, and the left leg far more often than the right, because the gravid uterus and the crossing right common iliac artery compress the left common iliac vein. The escalation there is a repeat or extended duplex with deliberate iliac insonation, or magnetic resonance venography, both of which answer it with no fetal dose. A contrast CT of the pelvis is the last resort in this patient, not the second study.
Reading a raised D-dimer in pregnancy or the puerperium as evidence of thrombosis, or a normal one as reassurance. It rises through normal gestation and does not settle for weeks after delivery, and the rule-out arm on this card deliberately stands aside in pregnancy for that reason — the scan is decided clinically in this group.

Priors — what to pull first

Check for a previous ultrasound in the same limb. Residual chronic thrombus is common after a treated event and produces an incompressible but organised vein; without the comparator it is repeatedly reported as recurrence, and recurrence means lifelong anticoagulation.
Note any indwelling catheter in an upper limb presentation — catheter-related thrombosis is managed differently from spontaneous upper limb thrombosis.

What makes a good request

A good request states the Wells score, the D-dimer result, which limb and which segment is symptomatic, whether interim anticoagulation has been given, and whether the patient is pregnant.
Timing is part of the recommendation, not an operational afterthought: a likely Wells score should have a proximal leg vein ultrasound within hours, and where that is not achievable, interim anticoagulation with a scan within a day is the accepted substitute.
Departments differ on whether calf veins are examined. A negative proximal study therefore does not have a single fixed meaning, and the report should state what was actually scanned so that the repeat-at-one-week question can be answered.

Scoring this once it is done

The classification and risk tools this question ends in.

Wells Score for Deep Vein Thrombosis Villalta Score for Post-Thrombotic Syndrome CEAP Classification

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

Venous duplex ultrasound for deep vein thrombosis CT Abdomen and Pelvis — Portal Venous Phase

Confirm locally

Venous duplex ultrasound for deep vein thrombosis: timings are typical — confirm against local protocol.
Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.