Correlation of estimated and measured glomerular filtration rate in patients with interposed bowel in the urinary tract

Objective. Isotope glomerular filtration rate (GFR) measurement is invasive, time-consuming and expensive. Estimated glomerular filtration rate (eGFR) is used as a surrogate, but has not been validated in patients whose lower urinary tract (LUT) is replaced with bowel. This study aimed to evaluate the correlation between the Modification of Diet of Renal Disease (MDRD) eGFR andchromium-51 ethylenediamine tetra-acetic acid (Cr-EDTA) GFR in patients with LUT reconstruction/diversion. Material and methods. A retrospective chart review was undertaken of 75 consecutive patients with LUT reconstruction/diversion attending scheduled follow-up in a single institutional setting. Cr-EDTA GFR, serum creatinine and eGFR were compared. Routine patient demographics, type of bowel reconstruction/diversionand time since surgery were noted. Results. The correlation between Cr-EDTA GFR and creatinine was poor (r(2) = 0.411) and the limits of agreement between variables were wide (-118 to +102, p = 0.053). The correlation between Cr-EDTA GFR and eGFR was slightly better (r(2) = 0.536), and the limits of agreement narrowed to -39 to +37 (p = 0.0003). The correlation was improved (r(2) = 0.623) when separating patients with renal failure (eGFR <= 60 ml/min per 1.73 m(2), n = 21), but the agreement between variables was poor (-20 to + 16 ml/min per 1.73 m(2), p = 0.424). Study limitations include the heterogeneous/complex patient population and types of bowel interposition, and asynchronous eGFR and Cr-EDTA GFR measurement (although no clinical events were recorded between measures). These reflect the reality in which eGFR is often used. Conclusions. There is poor correlation between eGFR and Cr-EDTA GFR in patients with LUT reconstruction/diversion with bowel. eGFR should be used with caution as a surrogate marker for isotope GFR in these patients. Larger prospective studies controlling for the study limitations identified are indicated.