Grant: Operating Grant

Two million Canadians currently suffer from chronic kidney disease (CKD). In 2006, 33,832 Canadians required either dialysis or kidney transplantation. These therapies are costly and associated with very high morbidity and mortality. One of the major hurdles in preventing the development of end-stage CKD is the under-recognition of deteriorating kidney function. The markers of kidney function currently in use are insensitive at detecting changes in kidney function and patients may lose substantial amounts of this without any biochemical evidence. This prevents the institution of appropriate treatments. In clinical trials, differences in therapies may not be appreciated. The best method of measuring kidney function is urinary clearance of the tracer inulin. Inulin is infused into a patient's bloodstream and the amount excreted in the urine is used to calculate kidney function. However, this is almost never performed due to its high cost and technical difficulty. In Canada, kidney function is measured by blood clearance of a radionucleotide tracer called 99mTc-DTPA. Current uncertainty in its supply due to aging reactors necessitates the search for alternatives. Non-radioactive iohexol is another promising tracer. Very few studies have examined the accuracy of blood clearance of iohexol and those that have are very small, of poor quality, and utilize a variety of different sampling techniques. None have included patients with significant edema (fluid overload) which is common in CKD. As a result, it is unclear how best to measure kidney function. The aim of this study is to determine the accuracy of blood clearance of iohexol in patients with and without edema. We propose to enroll CKD patients and measure urinary clearance of inulin and blood clearance of iohexol and 99mTc-DTPA. The over arching goal is to establish accurate protocols to measure kidney function that can be used in both patient care and clinical trials.