Krenning score
A 0-to-4 scale doctors use to describe how strongly a tumour lights up on a somatostatin receptor scan, by comparing it with the normal liver and spleen. A higher score generally means the tumour is a good candidate for peptide receptor radionuclide therapy.
Overview
The Krenning score is a five-point visual grading system (0-4) developed for planar and SPECT imaging with 111In-pentetreotide (OctreoScan), which grades tumour uptake of a somatostatin receptor tracer against two internal reference tissues: normal liver (grades 1-3) and spleen or kidney (grade 4). Grade 0 is no uptake; grade 1 is uptake below liver; grade 2 is uptake equal to or slightly less than liver; grade 3 is uptake greater than liver; grade 4 is uptake greater than spleen or kidney. The NETTER-1 trial required tumour uptake at least equal to normal liver (Krenning grade 2 or above) for enrolment, and a score greater than 2 is the practical threshold most centres use when selecting patients for PRRT with lutetium-177 dotatate.
The score has been extrapolated to gallium-68 and copper-64 DOTATATE PET/CT as a "modified Krenning score", but the correlation between the original scintigraphy-derived score and the PET-derived score is limited: PET is more sensitive, is acquired around one hour after injection rather than 24 hours, and tends to grade the same lesion higher. For lesions larger than 2 cm the modified score is considered more reliable; centres should state which imaging method and which reference organ underlie a reported grade.
The score is lesion-level and visual rather than quantitative, so heterogeneous disease (some lesions with low uptake alongside others with high uptake) requires reporting each discordant lesion separately rather than a single summary number, since a single index-lesion grade can misrepresent overall receptor status across the body.
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