Lymphedema diagnosis is dependent on visual assessment by clinicians. Clinical staging of lymphedema may be complicated by obesity. No quantitative metric is available to measure lymphatic function in patients with both lymphedema and obesity. To address this clinical need, we evaluated nodal uptake percent (NUP) at 120 min in relation to International Society of Lymphology stage and body mass index (BMI). This retrospective study included 20 patients with secondary lower extremity lymphedema, comprising 29 affected and 11 clinically unaffected limbs. NUP was calculated from lymphoscintigraphy. Limb comparisons and receiver operating characteristic (ROC) analyses stratified by BMI were performed. NUP differed among clinically unaffected limbs and ISL stage groups (p = 0.0028). Among patients with BMI < 35 kg/m², NUP was lower in stage 1 (p = 0.0243) and stage 2 (p = 0.0002) limbs than in unaffected limbs. Among those with BMI ≥ 35 kg/m², NUP ranged from reduced to preserved values overlapping the unaffected range. In the lower BMI group, the AUC was 0.9792 (95% CI, 0.9309–1.000). A cutoff < 0.4355% yielded 100% sensitivity and 87.5% specificity. NUP demonstrated its potential to complement clinical staging at BMI < 35 kg/m². However, these findings are hypothesis-generating and require independent external validation.