Table 3 Comparison of diagnostic modalities in GI-GVHD.

Endoscopic biopsy

Flexible sigmoidoscopy and histology

Gold standard for histological confirmation; highly specific.

Suboptimal sensitivity due to sampling error (inaccessible sites, patchy involvement); 48–72 h turnaround time for biopsy results; procedural risk; minimal prognostic information.

Conventional Imaging

CT, MR, US

Non-invasive, can evaluate inaccessible sites; sensitive; fast turnaround time for results; minimal patient risk.

Non-specific for GI-GVHD.

Positron Emission Tomography (PET)

[¹⁸F]FDG

[¹⁸F]GE-180

[¹⁸F]AraG

[⁶⁴Cu]OX40mAb

Non-invasive, can evaluate inaccessible sites; potential for high sensitivity and specificity by radiotracer selection; fast turnaround time for results; likely minimal patient risk, potential for GI-GVHD prediction and/or prognostication.

Cost of radiotracer investigation and/or production; radiotracer availability; requirement for radiotracer-specific quantitative assessment protocols; sensitivity/specificity for individual radiotracers needs evaluation in clinical trials.

Blood- and/or stool- based biomarkers

REG3α, ST2,

Faecal microbiome

Established link to GI-GVHD biology; predicts GI-GVHD onset and/or severity.

Diagnostic specificity, definition of “positive” test and optimal timing of measurement yet to be fully defined; turnaround time for individual patient results; requirement for validation in local populations.