Estimation of glomerular filtration rate in cancer patients with abnormal body composition and relation with carboplatin toxicity.

<bold>Purpose: </bold>Carboplatin clearance is correlated with glomerular filtration rate (GFR) and usually estimated with creatinine clearance using Cockcroft-Gault (CG) formula. Because plasma creatinine level is highly correlated with muscle mass, we hypothesized that an abnormal body composition with a low lean body mass (LBM) percentage [(LBM/weight) × 100] may result in inadequate carboplatin dosing. Serum cystatin C is an alternative marker of GFR, not affected by muscle mass. We aimed to investigate the influence of total LBM and LBM percentage on GFR calculation, using creatinine (CrCl) or cystatin C (GFRcysC-creat) in cancer patients.<bold>Methods: </bold>Pretreatment serum creatinine and cystatin C were prospectively measured in consecutive patients. CrCl (CG formula), GFRcysC-creat (CKD-EPI creatinine-cystatin equation), and LBM (CT scan) were calculated. Severe thrombocytopenia post-carboplatin were analyzed.<bold>Results: </bold>In 131 patients without renal insufficiency, LBM was correlated with creatinine (r = 0.30, p < 0.005) but not with cystatin C (r = -0.07, p = 0.43). In patients with the lowest LBM percentage, the CrCl was significantly higher than GFRcysC-creat indicating an overestimation of GFR with creatinine (p = 0.0004). In 24 patients treated with carboplatin AUC 5 (mg/ml min) ± paclitaxel, the risk of severe thrombocytopenia was associated with lower LBM percentage (p = 0.0002) and higher CrCl/GFRcysC-creat ratio (p = 0.006). By ROC analysis, the CrCl/GFRcysC-creat ratio threshold predicting severe thrombocytopenia was 1.23.<bold>Conclusions: </bold>A low LBM percentage increases the risk of inadequate GFR calculation by CG formula, and carboplatin overdosage with severe thrombocytopenia. High CrCl/GFRcysC-creat ratio allows the identification of these patients. [ABSTRACT FROM AUTHOR]