Infection & inflammation imaging
The same FDG tracer used to find cancer also lights up sites of infection and inflammation, which helps doctors find hidden abscesses, infected joint replacements or heart-valve infections that scans and blood tests alone can miss.
Overview
FDG PET/CT is now the best-evidenged nuclear medicine tool for infection and inflammation outside oncology, formalised in the EANM/SNMMI guideline/procedure standard for [18F]FDG hybrid PET use in infection and inflammation in adults, version 2.0 (Abikhzer et al., Eur J Nucl Med Mol Imaging 2025), which defines protocols and interpretation criteria across 19 indications, from bacteraemia and suspected spondylodiscitis to endocarditis, vascular graft infection and periprosthetic joint infection. For periprosthetic joint infection specifically, a pooled analysis cited in the guideline reports FDG PET sensitivity of about 85% and specificity of about 86% across 23 studies (1,437 patients), and the guideline states that the absence of periprosthetic uptake reliably excludes infection in both hip and knee prostheses, while a positive scan needs careful interpretation because aseptic loosening, recent surgery and metal-related artefact can all cause false-positive uptake.
White blood cell scintigraphy remains the preferred confirmatory test when FDG PET/CT is inconclusive, particularly for prosthetic joint and vascular graft infection, because it retains higher specificity than FDG in that specific setting even though FDG PET/CT is now the first-line hybrid imaging test for most of the 19 defined indications. A separate EANM/EBJIS/ESR consensus document (with ESCMID endorsement) sets out the broader multimodality diagnostic pathway for prosthetic joint infection, in which nuclear imaging is one component alongside clinical, microbiological and structural imaging criteria.
What the 2025 guideline explicitly flags as unresolved: it found insufficient evidence to support FDG PET/CT as a standard indication for COVID-19 (including long COVID), interstitial lung disease, or inflammatory arthropathies and myopathies, while noting evidence may emerge in future. SUV and target-to-background ratios, validated as semi-quantitative measures in oncology, have not been generally validated for distinguishing infection from sterile inflammation or malignancy and the guideline says they should be used with caution.
Notes
top- The 2025 EANM/SNMMI guideline found insufficient evidence to add COVID-19 (including long COVID), interstitial lung disease, or inflammatory arthropathies/myopathies as supported indications, though it leaves the door open as evidence accumulates.
- SUV and target-to-background ratios are not generally validated for distinguishing infection from sterile inflammation or malignancy, unlike their established role in oncology; the guideline recommends caution.
- White blood cell scintigraphy keeps a role as the confirmatory test when FDG PET/CT is inconclusive, especially around prosthetic joints, because false-positive FDG uptake from aseptic loosening or recent surgery is a recognised limitation.