Standardization of normal 99mTc-L,L EC clearance value in Indian population in comparison with two plasma sample method of glomerular filtration rate (GFR) estimation with 99mTc-DTPA

Introduction: Estimation of renal function in routine nuclear medicine studies is based on the parameters of ERPF and GFR. GFR measurement provides a valuable clinical methodology to quantify renal function. Two plasma sample method using 99mTc-DTPA is the gold standard method for estimation of nGFR, however, it requires skilled personnel due to its meticulous sample processing, standard preparation, radioactive counting and computation and has many potential sources of error. Furthermore, it needs additional counting equipment as gamma well counter. In a majority of Indian nuclear medicine centers, renal scintigraphy with 99mTc-L,L EC is performed as a routine procedure and renal function is assessed by determining effective renal plasma flow (ERPF), which measures the tubular function of kidneys. GFR can be derived from ERPF using filtration factor which is defined as the fraction of renal plasma flow that becomes glomerular filtrate. GFR with 99mTc-L, L -EC clearance has not been standardized in normal Indian population. Further, the filtration factor with 99mTc-L, L EC has not been standardized for normal healthy population. Hence, the present study was designed to establish standard values of 99mTc-L, L -EC clearance by using filtration factor in comparison to two sample method GFR estimation with 99mTc-DTPA.

Methods: The present study was designed to determine the filtration factor using ^99mTc-L, L EC and to standardize GFR values using GE-NM 830 dual head gamma camera equipped with LEHR collimator using modified gates method and compare them with GFR measurements estimated by two sample plasma as the standard. Well hydrated patients were recruited and asked to void before the examination. The procedure was explained to the patient and written informed consent was taken in normal healthy controls for estimation of GFR from ERPF with renal scintigraphy.

Results: Forty-one (28 female, 13 male) voluntary kidney donor patients with mean age 46.78 ± 8.91 years were included in the study. Mean GFR value normalized to body surface area (NGFR) estimated by 2-sample plasma method was 81.12 ±16.74 ml/min/1.73m2. The mean filtration factor for derivation of GFR (dGFR) from ERPF for Tc-L, L -EC was estimated to be 0.17±0.04. Accordingly, the mean dGFR was 78.53±13.77 mL/min/1.73m2. Both NGFR and ERPF data were normally distributed with no statistically significant difference (p = 0.37 and 0.53, respectively).

Conclusions: GFR can be estimated from ERPF with ^99mTc-L, L -EC-renal scintigraphy by using a filtration factor of 0.17 ± 0.04 in normal Indian population. This method reliably and reproducibly estimates GFR and alleviates the need of two sample plasma method for GFR estimation.