Can a patient with impaired renal function (dialysis patient) undergo a Ventilation-Perfusion (VQ) scan?

Can a Dialysis Patient Have a VQ Scan?

Yes, dialysis patients can and should undergo VQ scanning when pulmonary embolism is suspected, as it is the preferred imaging modality in this population to avoid contrast-induced complications. 1, 2

Why VQ Scanning is Preferred in Dialysis Patients

VQ scanning avoids iodinated contrast exposure, which is particularly important in dialysis patients who may have residual renal function that could be further compromised by contrast agents. 1 The European Society of Cardiology specifically recommends V/Q scanning as an alternative to CT pulmonary angiography in patients with contraindications to CT contrast. 1

• Residual renal function preservation: Some dialysis patients retain residual kidney function, and contrast exposure could eliminate this remaining function, which is associated with better outcomes and quality of life. 3
• No additional renal toxicity risk: Unlike CT angiography with iodinated contrast, VQ scanning uses radiotracer agents that do not pose nephrotoxic risks. 1

Clinical Evidence Supporting VQ Scanning in Renal Impairment

A dedicated study evaluated VQ scanning specifically in patients with impaired renal function and found it to be a viable diagnostic option. 2 While the positive predictive value for high-probability scans was modest (30%), combining VQ scan results with clinical probability scoring (Wells' score ≥7) improved the positive predictive value to 72%. 2

• Negative predictive values were approximately 79% for low probability and 67% for moderate probability results, making VQ scanning effective for ruling out PE in dialysis patients. 2
• In clinical practice, patients with impaired renal function and high-probability VQ scans were appropriately treated with anticoagulants when CT angiography was contraindicated. 2

Optimal VQ Scan Protocol for Dialysis Patients

Both ventilation and perfusion components should be performed for optimal diagnostic accuracy, with multiple views obtained to reduce indeterminate results. 1

• Ensure a current good-quality chest radiograph is available before performing the VQ scan for comparison. 1
• Provide clinical probability assessment (Wells score or revised Geneva score) to the interpreting physician before the scan. 1
• Reports should use validated criteria such as modified PIOPED or PISA-PED methods, categorizing findings as normal, high probability, or non-diagnostic. 1

Diagnostic Algorithm for Suspected PE in Dialysis Patients

1. Assess clinical probability using Wells score or revised Geneva score. 1
2. Measure D-dimer if clinical probability is low or intermediate (though D-dimer has limitations in dialysis patients due to chronic inflammation). 4
3. Proceed directly to VQ scanning rather than CT angiography to avoid contrast exposure. 1
4. Interpret results in context:
   • Normal VQ scan effectively rules out PE. 1
   • High-probability scan confirms PE, especially when Wells' score ≥7. 2
   • Non-diagnostic scans require further evaluation, potentially including lower limb compression ultrasonography. 1

Important Caveats and Limitations

VQ scan interpretation may be challenging in dialysis patients with comorbid conditions such as chronic obstructive pulmonary disease, left heart failure (common in dialysis patients), or previous pulmonary embolism. 1 Approximately 30-50% of VQ scans may be non-diagnostic and require additional testing. 1

Avoid using positive D-dimer alone to diagnose PE in dialysis patients, as chronic inflammation and comorbidities frequently elevate D-dimer regardless of thrombotic disease. 4 Confirmation with imaging is always required. 4

For dialysis patients on the transplant waitlist requiring cardiovascular evaluation, baseline ECG and echocardiography should be obtained within 1-3 months after achieving dry weight, with periodic reassessment as clinically indicated. 3, 5