Technetium-99m(V)–Citrate Complex for Estimation of Glomerular Filtration Rate

Abstract

THE standard compound used for estimating the rate of glomerular filtration is inulin, but its chemical determination is tedious and time consuming. The technique for estimating the filtration rate with inulin requires constant infusion and serial urine collections. ¹⁴C-carboxyl-, ¹³¹I- and ¹²⁵I-allyl-inulin have been suggested, but chemical instability, cost and lack of rapid and simple methods of analysis have limited their use^1–3. A compound labelled with a gamma emitting isotope and excreted entirely by glomerular filtration would make the study of renal function much easier, and ¹³¹I- (also ¹²⁵I-) dia-trizoate^4,5, ¹³¹I- (also ¹²⁵I-) iothalamate⁶, ⁵⁷Co-vitamin B₁₂ (refs. 7–9), and ⁵¹Cr-ethylenediamine tetraacetate¹⁰ have received attention. There are, however, disadvantages in using these labelled compounds for estimating the rate of glomerular filtration when successive examinations are attempted in the presence of poor or rapidly declining renal function. In these conditions, the radioactivity of plasma tends to increase to levels great enough to reduce the accuracy of the measurements, because of the relatively long half life of these nuclides. ⁵⁷Co-vitamin B₁₂ has two further disadvantages: it is appreciably bound to plasma protein¹¹, and it has a long residence time in the liver so that its repeated use in a patient with seriously impaired renal function would be undesirable.