2026 Volume 76 Issue 2 Pages 129-135
Background & Aims: The lumbar-to-kidney ratio (LKR) has been traditionally used as a standard internal reference for bone metastasis evaluation on bone scintigraphy. However, in patients with renal impairment, increased renal uptake may lead to underestimation of LKR. We evaluated the usefulness of the lumbar-to-background ratio (LBR), using femoral soft tissue as a reference, and developed a corrected LBR score (cLBR) incorporating body mass index (BMI) and estimated glomerular filtration rate (eGFR).
Methods: We studied 163 cancer patients who underwent bone scintigraphy. Diagnostic performance of LKR and LBR was compared using ROC analysis, with stratification by eGFR (threshold: 60 mL/min/1.73m2). BSI≥0.5％ was defined as positive.
Results: Overall, AUC was 0.646 for LKR and 0.687 for LBR. In the stratified analysis, the normal renal function group (n＝114) showed similar performance (LKR 0.656 vs LBR 0.648), whereas the impaired renal function group (n＝49) showed markedly superior performance of LBR (0.754) compared to LKR (0.579), with a difference of ＋0.175. A strong negative correlation was observed between eGFR and renal uptake (r＝－0.445). The multivariate model (cLBR score) incorporating BMI and eGFR achieved an AUC of 0.733.
Conclusions: In patients with renal impairment, LKR showed reduced diagnostic performance, while LBR may maintain higher diagnostic accuracy. As a pilot study, these findings suggest that LBR using femoral background warrants further investigation in larger cohorts.
