Suspected pulmonary embolism in a patient who cannot have contrast

Probability assessment

• Using the Wells score: clinical signs of DVT (0), PE as likely as or more likely than an alternative diagnosis (+3), heart rate >100 (+1.5), immobilisation/surgery within 4 weeks (+1.5), previous VTE (0), haemoptysis (0), malignancy (0). Total ≈ 6 → PE likely.
• In the 'PE likely' group, a D-dimer is not used to rule out PE: it lacks the negative predictive value needed, and the D-dimer will be raised anyway after recent surgery. The pathway goes straight to imaging.

Why this matters

• The judgement point is that the Wells category, not the D-dimer, drives the next step. A negative D-dimer here would not be reassuring.
• She is haemodynamically stable (BP 128/78), so she is not in high-risk PE; she does not need immediate thrombolysis, and there is time to confirm the diagnosis. But confirmation must not be so delayed that she goes untreated - if imaging is delayed, start therapeutic anticoagulation empirically unless contraindicated.

CT pulmonary angiography is the usual first-line test but is relatively contraindicated here:

• eGFR 28 mL/min/1.73m² means contrast nephropathy risk is significant, and she has a prior anaphylactoid reaction to iodinated contrast.

Preferred option: ventilation–perfusion (V/Q) SPECT imaging.

• V/Q imaging requires no iodinated contrast and is validated for PE diagnosis.
• It is most useful when the chest radiograph is normal - as here - because a normal radiograph removes many causes of matched defects.
• A normal V/Q scan effectively excludes PE; a high-probability scan with compatible clinical probability confirms it.

If V/Q is non-diagnostic:

• Do not simply abandon imaging and treat blindly for months. Options include catheter-directed or non-contrast MR angiography where available, or a discussion weighing the risk of a second contrast exposure against the harm of missed PE.
• Meanwhile she should be anticoagulated if there is no bleeding contraindication.

The answer being tested is the deliberate choice of a non-contrast test rather than defaulting to CTPA and accepting renal injury and a repeat allergic reaction.

Risk stratification first

• Stable blood pressure and no troponin/BNP evidence of right ventricular strain would place her in the low-risk group, but she has multiple comorbidities, so she likely needs admission at least initially.

Anticoagulant choices with eGFR 28:

• LMWH (enoxaparin) is acceptable but should be dose-adjusted for renal function (often 1 mg/kg once daily rather than twice daily) or monitored with anti-Xa levels; accumulation is a real risk.
• Fondaparinux is best avoided: it is contraindicated at creatinine clearance below 30 mL/min because of accumulation and bleeding risk.
• DOACs: apixaban is the least renally dependent and can be used with caution in this range; dabigatran and edoxaban are less suitable, and rivaroxaban should be avoided at this level of impairment.
• Unfractionated heparin is the safest choice if renal function is unstable or likely to deteriorate further, because it is not renally cleared and is easily reversed.

Practical points: correct the eGFR for body size, recheck renal function during intercurrent illness, and give a clear sick-day plan. Duration is at least 3 months and should be reviewed against whether the provoking factor (surgery) has resolved - provoked VTE after major surgery may justify stopping at 3 months, whereas unprovoked VTE warrants consideration of extended therapy.