A comparison of simplified and standard methods for the measurement of glomerular filtration rate and renal tubular function.

Two methods of measuring the clearance of 99Tcm DTPA, OIH and iothalamate were compared with standard techniques of measuring the clearance rates of inulin and sodium para-aminohippurate. The best correlation was between the clearance of subcutaneously injected radiolabelled iothalamate or 99Tcm DTPA and that of inulin. 99Tcm DTPA and 131I OIH clearances measured by a two blood sample technique did not give as good a correlation with inulin and PAH clearances respectively. When measurements of GFR and tubular function were repeated on the same patients the changes measured by inulin and PAH clearances did not correlate with those measured by the two blood sample technique using 99Tcm DTPA and OIH. Our results suggest that the clearance of subcutaneously injected iothalamate or DTPA can replace inulin clearance measurements. The two blood sample technique of measuring DTPA and OIH clearance does not directly reflect inulin and PAH clearance and is insufficiently reproducible to be used to follow changes in renal function.