Re: Low eGFR and high albuminuria predict end stage kidney disease and death at all ages
DETECTION OF RENAL INSUFFICIENCY IN THE ELDERLY: doing what we should rather than perpetuating clinical habits
1A Michael Peters and 2A Robert Michell
1Brighton Sussex Medical School, Audrey Emerton Building, Eastern Road, Brighton BN2 5BE
Tel: 01273 523360
Fax: 01273 523366
2Pinecroft, Upper Cleveley, Oxon OX7 4DX
(Formerly: Department of Biochemical Pharmacology, Harvey Institute, St Bartholomew’s Hospital, London)
Tel: 01608 677555
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A progressive decline in glomerular filtration rate (GFR) is an inevitable consequence of growing old. In healthy kidney transplant donors, GFR decreases by about 25% between the ages of 35 and 70 depending on gender, being faster in women.1 An increase in the use of an expanding range of medications for various minor and major health problems that affect increasing numbers of patients is also an inevitable consequence of increasing longevity. There is therefore a growing need to adjust drug dosage to reflect diminished renal function of which GFR is the best measure in order to avoid unpleasant or dangerous side effects. This need, however, is unlikely to be met if measurement of GFR requires the inconvenience for the patient of attending a suitable hospital (of which only a minority have the facilities for accurately measuring GFR) and burdens the NHS with the cost. Much has been made of the use of GFR estimated from plasma creatinine (eGFR) as a clinical proxy for ‘true’ GFR. However, not only is eGFR a poor proxy for GFR but its validity is largely based on comparisons with ‘gold standard’ GFR in populations that have seldom included adequate numbers of elderly patients. Moreover, it is beyond doubt that eGFR is least reliable when muscle mass has been lost or creatinine turnover is affected by disease or debility, as is especially likely in older patients. To quote the BNF (2006, p18-19) ‘Old people, especially the very old, require special care and consideration from prescribers…..The most important effect of age is reduction in renal clearance.’ In short, they deserve better than eGFR.
There have long been sophisticated computer algorithms available for adjusting drug dosage in the face of compromised renal clearance but they depend on reasonably accurate measurement of residual GFR. Several groups, including ourselves (with the support of the previously named NKRF), have described such a method of measurement based on iohexol that can be performed in the GP practice or even in the patient’s home, because, as the indicator is completely stable and nonradioactive, it is the blood sample that travels rather than the patient2,3. The stability of iohexol in the samples would allow a single laboratory to service the entire UK (plus, potentially, samples from overseas or from veterinary practices), thus maximising sample throughput and cost-effectiveness as well as eliminating inter-laboratory variations.
A recent NHS report4 estimated that about one million people in the UK have undiagnosed chronic kidney disease in addition to the 1.8 million who do have a diagnosis and whose clinical needs consume £1 in every £77 spent by the NHS. Quite apart from the benefits of treating chronic kidney disease at an earlier stage, home or primary care measurement of GFR would allow patients to receive more appropriate drug dosages and to avoid the adverse effects of over- or under-medication, including unnecessary withdrawal of drugs. The method is simple, safe and both cheaper and better than current practice: it is time for current practice to change.
1. Peters AM, Perry L, Hooker CA, Howard B, Neilly MDJ, Seshadri N, et al. Extracellular fluid volume and glomerular filtration rate in 1,878 healthy potential renal transplant donors: effects of age, gender, obesity and scaling. Nephrol Dial Transplant. 2012;27:1429-37.
2. Niculescu-Duvaz I, D'Mello L, Maan Z, Barron JL, Newman DJ, Dockrell ME, et al. Development of an outpatient finger-prick glomerular filtration rate procedure suitable for epidemiological studies. Kidney Int. 2006;69:1272-5.
3. Bird NJ, Peters C, Michell AR, Peters AM. Suitability of a simplified technique based on iohexol for de-centralised measurement of glomerular filtrstion rate. Scand J Urol Nephrol. 2008; 42:472-80.
4. NHS Kidney Care. Chronic kidney disease in England: the human and financial cost. www.kidneycare.nhs.uk. August 2012.