What are the InterSocietal Accreditation Committee (IAC) amendments to the Society of Radiologists in Ultrasound (SRU) carotid artery consensus criteria?

IAC Amendments to SRU Carotid Artery Consensus Criteria

The InterSocietal Accreditation Commission (IAC) released updated recommendations in 2023 that modify the original Society of Radiologists in Ultrasound (SRU) consensus criteria, most notably raising the peak systolic velocity (PSV) threshold for ≥50% internal carotid artery (ICA) stenosis from ≥125 cm/s to ≥180 cm/s, while maintaining the PSV >230 cm/s threshold for ≥70% stenosis 1.

Key Amendments from IAC (2023)

Primary Changes to Stenosis Thresholds

The IAC modifications address a critical problem: the original SRU consensus criteria (SRUCC) from 2003 significantly overestimated the degree of carotid stenosis when validated against catheter angiography 1.

For ≥50% ICA Stenosis:

• Original SRU criteria: PSV ≥125 cm/s (single parameter)
• IAC amended criteria: PSV ≥180 cm/s as primary parameter, OR maintain PSV ≥125 cm/s but require ICA/CCA PSV ratio ≥2.0 as an additional mandatory parameter 1

For ≥70% ICA Stenosis:

• Both SRU and IAC: PSV >230 cm/s remains the primary threshold 2, 3, 4, 1
• Additional supporting criteria: ICA/CCA ratio >4 and end-diastolic velocity (EDV) >100 cm/s 2, 3

Performance Improvements

The IAC amendments substantially improve diagnostic accuracy:

• Original SRUCC for ≥50% stenosis: Sensitivity 97.8%, specificity only 64.2%, accuracy 74.5%
• IAC amended criteria (PSV ≥180 cm/s): Sensitivity 93.3%, specificity 81.6%, accuracy 85.2%
• Alternative IAC approach (PSV ≥125 + ratio ≥2.0): Sensitivity 94.3%, specificity 84.3%, accuracy 87.4% 1

Clinical Impact of Adopting IAC Criteria

Effect on Patient Categorization

A 2026 study demonstrated the real-world impact of these changes 5:

• Using PSV >230 cm/s alone (IAC threshold) resulted in a 52% increase in patients categorized as ≥70% stenosis compared to higher institutional thresholds
• However, when multiple parameters are incorporated (EDV >100 cm/s AND ICA/CCA ratio >4), the difference becomes statistically insignificant (only 1.1% increase, p=0.317) 5

This finding is critical: The IAC amendments emphasize that PSV should be the primary parameter, but multiple parameters must be used together to avoid false-positive diagnoses that could lead to unnecessary interventions.

Why the Amendments Were Necessary

Problems with Original SRU Criteria

Multiple validation studies revealed serious flaws:

1. Poor predictive ability: One study found the SRU criteria for ≥70% stenosis had an area under the ROC curve of only 0.51—essentially no better than chance 6

2. Systematic overestimation: Agreement between duplex using SRUCC and angiography was only moderate (κ=0.42), with consistent overestimation of both moderate and severe stenosis 1

3. Laboratory variability: The 2011 multi-society guidelines documented extreme variability across laboratories, with PSV cutpoints for 60% stenosis ranging from 151 to 390 cm/s across different centers 2, 3

Practical Application Algorithm

When interpreting carotid duplex for stenosis severity:

1. Measure all parameters: PSV, EDV, and ICA/CCA ratio—never rely on PSV alone

2. For ≥50-69% stenosis classification:

   • Require PSV ≥180 cm/s (IAC threshold)
   • Confirm with ICA/CCA ratio 2-4
   • EDV should be 40-100 cm/s
   • Must visualize plaque on gray-scale imaging 2, 3, 1

3. For ≥70% stenosis classification:

   • Require PSV >230 cm/s
   • AND ICA/CCA ratio >4
   • AND EDV >100 cm/s
   • Must visualize significant plaque and luminal narrowing 2, 3, 5

4. When parameters are discordant: Consider confirmatory imaging with CTA or MRA before making treatment decisions 3, 7

Important Caveats

Situations Requiring Adjusted Interpretation

The IAC criteria maintain awareness of conditions that alter velocity measurements 2, 3:

• Higher velocities in women compared to men (physiologic)
• Contralateral carotid occlusion elevates ipsilateral velocities through compensatory flow
• Post-stenting: In-stent velocities are inherently elevated due to decreased vessel compliance
• Severe tortuosity, high bifurcation, obesity, extensive calcification: All reduce ultrasound accuracy

When Ultrasound May Fail

Critical limitation: Duplex cannot reliably distinguish subtotal occlusion from complete occlusion—a distinction with major treatment implications 2, 3. In these cases, catheter angiography may be necessary 3, 7.

Comparison with International Criteria

The 2024 European Society of Cardiology guidelines reference both SRUCC and the work by Gornik et al. (which informed the IAC amendments), noting that the original SRUCC criteria lead to overestimation but acknowledging no complete consensus has been reached 4. The multiparametric German DEGUM approach shows better specificity (70.2%) than SRU criteria (56.4%) for severe stenosis, supporting the IAC's multi-parameter strategy 8.

Quality Assurance Mandate

The IAC amendments emphasize that all laboratories must validate their criteria against catheter angiography and implement ongoing quality assurance programs comparing findings across imaging modalities 3. This is not optional—it's essential for maintaining diagnostic accuracy given the documented inter-laboratory and inter-device variability 2, 3.