Yes, Infection and Inflammation Cause Elevated SUV
Both infection and inflammation routinely cause elevated standardized uptake values (SUV) on FDG-PET imaging, representing a major source of false-positive results when attempting to distinguish malignant from benign lesions. This occurs because FDG accumulates in any cells with increased glucose transporter expression, including immune cells at sites of infection and inflammation 1.
Mechanism and Clinical Impact
- FDG uptake reflects glucose metabolism, which is elevated not only in malignant lesions but also in activated immune cells responding to infectious and inflammatory processes 1
- False-positive PET results occur most commonly from infectious and inflammatory lesions, and less frequently from sarcoidosis and rheumatoid nodules 1
- The specificity of FDG-PET/CT for differentiating benign from malignant lesions drops dramatically in regions with high prevalence of infections—as low as 25% in areas with endemic tuberculosis 1, 2
Geographic and Clinical Context Matters
- In non-endemic regions, FDG-PET/CT specificity for pulmonary nodules is 77% (95% CI, 73%-80%), but this decreases to 61% (95% CI, 49%-72%) in endemic infectious disease regions 1
- Fungal infections account for 16 of the false-positive cases in one large surgical series, demonstrating the significant impact of infectious processes on SUV elevation 3
- The variable FDG uptake in thoracic lesions (lungs and mediastinal lymph nodes) is directly associated with the high prevalence of inflammation and infection within the chest 4
SUV Thresholds Cannot Reliably Distinguish Infection from Malignancy
- While one study in a coccidioidal endemic region found all nodules with SUVmax >5.9 were malignant, there was significant overlap below this threshold, with sensitivity of only 69% at this cutoff 1
- The intensity of FDG uptake itself (SUV or target-to-blood pool ratio) has not been shown to reliably differentiate infection from inflammation or malignancy 1
- Different anatomical regions require different SUV thresholds due to varying prevalence of inflammatory conditions—thoracic lesions require higher thresholds (>3.6) compared to extrathoracic regions (>2.2) specifically because of higher chest inflammation/infection rates 4
Pattern Recognition Over Quantitative Values
- FDG uptake pattern provides better discrimination than SUV alone: focal uptake suggests infection while homogeneous uptake along a region suggests aseptic inflammation 1
- Visual assessment by experienced readers often outperforms strict SUVmax cutoffs, achieving sensitivity of 96-100% and specificity of 76-86% 2, 5
- Integration of clinical context, morphologic CT features, and quantitative values is essential rather than relying on SUV thresholds alone 2
Specific Infectious Conditions and SUV Elevation
- Spine infections demonstrate increased FDG uptake with elevated SUVmax values, with FDG-PET/CT showing 94.8% sensitivity and 91.4% specificity for spinal infection 1
- Tuberculous spondylodiscitis shows significantly higher median SUVmax (12.4) compared to pyogenic spondylodiscitis (7.3), though overlap exists 1
- Complex tuberculosis cases with higher SUVmax correspond with larger numbers of affected organ systems and longer required therapy duration 6
Critical Clinical Pitfalls to Avoid
- Never assume elevated SUV indicates malignancy in regions with endemic infections—tissue diagnosis becomes critical regardless of SUVmax value 1, 2
- Timing matters: avoid FDG-PET/CT within 2-3 months after radiation therapy due to radiation-induced inflammation, and wait at least 6 weeks after surgery due to postsurgical inflammation 1
- Recent chemotherapy (within 10 days) and growth factor use (within 2 weeks) can cause false-positive results from bone marrow activation 1
- In patients with cardiac device infections, focal FDG activity higher than liver intensity is more likely infection, but SUV alone cannot reliably differentiate infection from inflammation 1