β-Trace Protein Is an Alternative Marker for Glomerular Filtration Rate in Renal Transplantation Patients

Abstract

Careful monitoring of graft function after renal transplantation (RTx) is necessary for short- and long-term success. Because of the many difficulties in performing serial measurements of glomerular filtration rate (GFR) by use of exogenous substances such as inulin, 51Cr-EDTA, or technetium-diethylenetriaminepentaacetic acid (99mTc-DTPA), graft function is often estimated from serum creatinine concentrations. Tubular secretion as well as various nonrenal factors may alter creatinine concentrations, thus rendering it an imprecise marker for GFR (1). Cystatin C (Cys C) is at least as good as creatinine as a marker of renal function (2)(3)(4), but corticosteroid treatment can alter serum Cys C concentrations (5)(6)(7), making it potentially less useful in RTx patients. β-Trace protein (BTP), also known as prostaglandin D synthase, is a 23- to 29-kDa enzyme that has been proposed as an alternative marker for GFR in children and in persons with diabetes or various renal diseases (8)(9)(10)(11), but it has not been examined as an endogenous renal function marker in RTx patients. The aim of this study was to compare the diagnostic performances of BTP, Cys C, and creatinine as estimates of GFR in RTx patients. We prospectively performed GFR measurements in 85 consecutive RTx patients (34 females and 51 males) who attended our outpatient department. GFR was determined by 99mTc-DTPA clearance with a single-injection technique based on the method described by Russell et al. (12). Patients included into the study were in “steady-state” conditions, defined as the lack of increases or decreases >15% in creatinine within 2 weeks before and after the investigation. The mean (SD) patient age was 49.6 (13.3) years (range, 19–72 years), and the time frame of investigation was 75.7 (71.2) months after transplantation (range, 3–240 months; 21 patients …