Estimation of glomerular filtration rate as a predictor of renal impairment in egyptian systemic sclerosis patients, a comparative study between the classic gates method using TC99M DTPA and the cockcroft and gault formula: correlation with disease severity

ABSTRACT

Prognosis of Systemic sclerosis largely depends on involvement of internal organs. Kidney affection has the worst prognosis and highest mortality rate. Aim was to evaluate renal impairment in patients with systemic sclerosis by measuring the Glomerular filtration rate and then calculating the GFR using the Cockcroft and Gault formula and the Modification of Diet in Renal Disease equation [MDRD] formula and test the accuracy of these formulae. The study included 31 scleroderma patients [27 females, 4 males] recruited from the Rheumatology and Rehabilitation Department, Cairo University hospitals, mean age 43.25 +/- 11.28 years, 16 had limited systemic sclerosis, 12 diffuse systemic sclerosis and 3 had overlap syndrome. Therty-one age and sex matched healthy controls were included. Estimation of disease severity was done using disease severity index. GFR was measured using TC99mDTPA. The modified Cockcroft and Gault formula and equation 7 from the Modification of Diet in Renal Disease [MDRD] were used. A measured GFR within normal [>89ml/min] was found in 14 patients [45.1%] with normal kidney function and serum creatinine. Reduced GFR was reported in 17 patients [54.9%], it ranged from 60-89ml/min with mild renal impairment in 10 patients [32.3%], and ranged from 30-59ml/min showing moderate functional impairment in 7 patients [22.6%], none of our patients had severe renal impairment according to the Gates method for measuring the GFR. The formulae used succeeded to detect reduction of GFR in 35.29% of those affected using the Cockcroft-Gault and in 41.17% of those affected using the MDRD. A positive correlation was found between MDRD and measured GFR, furthermore, the decline in the GFR didn't show any correlation with disease severity. A positive correlation was also reported between the presence of renal involvement and pulmonary vascular involvement in the group under study p=0.04. Measurement of the GFR using Gates method showed reduction of the GFR in 54.9% of the SSc patients under study. Serum creatinine was an insensitive tool for evaluating renal functional impairment. The formulae used weren't as precise as the measured GFR in diagnosing all cases with subclinical renal involvement in the studied population. Patients with systemic sclerosis should be screened for renal involvement irrespective of disease severity or duration