Measurement of glomerular filtration rate in cats

PRACTICAL RELEVANCE: Routinely used markers of renal function in clinical practice include urea and creatinine. However, these are insensitive markers, particularly in the early stages of kidney disease. Measurement of glomerular filtration rate (GFR) is regarded as the most sensitive index of functioning renal mass. It may be useful for feline patients in varying clinical scenarios; for example, where a more accurate measurement of renal function may aid diagnosis, to enable response to therapeutic interventions to be more closely monitored, or to evaluate renal function prior to the use of nephrotoxic or renally cleared drugs. CLINICAL CHALLENGES: Traditional methods of measuring GFR, such as renal clearance or multisample plasma clearance techniques, are generally impractical for clinical use. Limited sampling and single sample plasma clearance methods using the filtration marker iohexol have been validated in cats. These have the advantages of reduced stress to cats associated with repeated sampling and reduced costs of analysis, and therefore offer greater clinical utility. Attempts to develop an estimated GFR (eGFR) formula similar to that used in human patients have been made in cats, although currently an accurate and reliable formula is not available. AUDIENCE: This review presents the basis for the theoretical understanding and practical measurement of GFR for any veterinary practitioner wishing to obtain a more accurate and sensitive assessment of renal function than routinely used markers provide. EVIDENCE BASE: The review draws evidence from peer-reviewed publications, the author's PhD thesis and also clinical experience.