Physiological testicular ¹⁸F-FDG uptake in boys: age-related patterns and association with body mass index

To characterize age-related patterns of testicular ¹⁸F-Fluorodeoxyglucose (FDG) uptake in boys and evaluate association with body mass index (BMI).

Testicular SUV_max, SUV_mean and testicle-to-liver ratio (TLR) of boys aged 0-18 years selected by stratified random sampling were measured and compared across age groups. Age-stratified reference values were established. Age-related metabolic transition points were identified using classification and regression tree (CART) models. Multivariable regression analyses were performed to assess association between BMI and testicular FDG uptake.

In 377 boys (mean age, 8.0 ± 5.3 years), testicular ¹⁸F-FDG uptake increased with age, correlating strongly with SUV_max (r = 0.792) and SUV_mean (r = 0.753), moderately with TLR (r = 0.506), (all P < 0.001). Three age-related metabolic patterns were identified: low uptake at 0-8 years, transitional increase at 9-12 years, and sustained higher uptake at 13-18 years. Corresponding SUV_max 97.5th percentiles were 2.5-2.9, 5.2-5.3, and 5.9-6.5. CART identified a metabolic transition at 10.5-12.5 years. Multivariate analysis identified age as the dominant predictor for testicular FDG uptake (SUV_max: β = 0.689, SUV_mean: β = 0.638, TLR: β = 0.501; all P < 0.001). After age adjustment, higher BMI remained independently associated with increased uptake (SUV_max: r = 0.398; SUV_mean: r = 0.412; both P < 0.001). Metabolic transition points varied among BMI groups, with 10.5, 11.5, and 12.5 years in the overweight, normal-weight, and underweight groups, respectively.

Physiological testicular ¹⁸F-FDG uptake demonstrates distinct age-related patterns across childhood and adolescence. Age-stratified descriptive values provide quantitative reference data for pediatric PET interpretation. BMI is independently associated with testicular FDG uptake.