[Comparison of six radionuclidic and non-radionuclidic methods for the assessment of glomerular filtration rate in patients with chronic renal failure].

The assessment of renal function in patients with chronic renal failure has a significant impact on both prognosis and treatment. We were unable to find a study, comparing six radionuclidic and non-radionuclidic methods as tested in this study on the same patients for the assessment of renal function in order to evaluate the relative significance of each method. In this study 82 patients were enrolled, 31 females with an age range 18-73 y (mean: 46 y) and 51 males with an age range 20-77 y (mean: 48 y). The level of renal function of these subjects ranged between normal, and mild to severe renal failure with serum creatinine levels: 2.7+/-2.2 mg/dl (mean+/-SD). The methods used for the glomerular filtration rate (GFR) were: (a) the clearance of inulin; (b) the technetium 99m labeled-diethyleno triamine pentacetic acid (99m)Tc-DTPA plasma disappearance curve; (c) the UV/P formula, not corrected for the residual urine volume in the bladder [DTPA(-)]; (d) the UV/P formula corrected for the residual urine volume in the bladder [DTPA(+)]; (e) plasma clearance of creatinine by the Cockcroft-Gault formula; and (f) plasma clearance of creatinine by using a 24-hour urine collection. In a subgroup of 13/82 patients, GFR was assessed by the radionuclidic and non-radionuclidic methods and compared against clearance of inulin, which was considered to be the gold standard. Moreover, we evaluated in our results the impact of age, gender, cause and stage of renal failure and the effect of the residual urine volume in the bladder. Fifteen of our patients were re-evaluated after 19-21 weeks. Spearman's correlation was used for statistical analysis; a two-sided P value < 0.05 was considered as statistically significant. Our results have shown that: the DTPA(+) method displayed the best correlation with the clearance of inulin (r=0.996) and was considered as the reference method in this study. The radionuclidic methods (99m)Tc-DTPA) plasma disappearance curve and DTPA(-) gave similar and comparable results with DTPA(+) (r=0.98, r=0.96), while the non-radionuclidic methods(plasma clearance of creatinine by using a 24-hour urine collection and plasma clearance of creatinine by the Cockcroft-Gault formula) tended to overestimate GFR respectively(r=0.91, r=0.79). Patient's age and gender had no impact on the calculated GFR values. With regards to the chronic renal failure cause, the above-mentioned tendencies were confirmed in primary and secondary glomerulonephritis, in diabetic nephropathy, and in hereditary renal diseases. On the contrary, in patients with renal disease of unknown cause, all methods -- isotopic and non-isotopic -- gave comparable results. The DTPA(-) method is simple to use and reliable, however, due to the fact that it does not consider the residual urine volume in the bladder, it seems to overestimate GFR in elderly men with prostate hypertrophy and increased residual urine volume in the bladder. The DTPA(+) method is reliable in a wide range of renal function levels, from mild to significant renal impairment. The radionuclidic methods DTPA(+), DTPA(-) and the (99m)Tc-DTPA plasma disappearance curves showed a very good reproducibility (r =0.97, r =0.96, r = 0.87) when were reperformed after 19-21 weeks, as compared to creatinine clearance with 24-hour urine collection (r=0.83). In conclusion, the radionuclidic methods in patients with chronic renal failure are reliable and reproducible, closely resembling those of inulin clearance. The among all radionuclidic methods, (99m)Tc-DTPA(+) shows the best results.