Blog entry by Meguid El Nahas
That eGFR is NOT a measure of KIDNEY FUNCTION but instead a CALCULATION/DERIVATION reflecting serum creatinine levels!?
In this month, KI (April 2013): Turin and colleagues from Alberta in Canada show data suggesting that changes in eGFR over time; declining and increasing are associated with increased were independently associated with mortality. http://www.ncbi.nlm.nih.gov/pubmed/23344477
Abstract: Using a community-based cohort we studied the association between changes in the estimated glomerular filtration rate (eGFR) over time and the risk of all-cause mortality. We identified 529,312 adults who had at least three outpatient eGFR measurements over a 4-year period from a provincial laboratory repository in Alberta, Canada. Two indices of change in eGFR were evaluated: the absolute annual rate of change (in ml/min per 1.73 m(2) per year) and the annual percentage change (percent/year). The adjusted mortality risk associated with each category of change in eGFR was assessed, using stable eGFR (no change) as the reference. Over a median follow-up of 2.5 years there were 32,372 deaths. Compared to the reference participants, those with the greatest absolute annual decline less than or equal to 5 ml/min per 1.73 m(2) per year had significantly increased mortality (hazard ratio of 1.52) adjusted for covariates and kidney function at baseline (last eGFR measurement). Participants with the greatest increase in eGFR of 5 ml/min per 1.73 m(2) per year or more also had significantly increased mortality (adjusted hazard ratio of 2.20). A similar pattern was found when change in eGFR was quantified as an annual percentage change. Thus, both declining and increasing eGFR were independently associated with mortality and underscore the importance of identifying change in eGFR over time to improve mortality risk prediction.
OLA BLOG COMMENT:
Throughout the discussion the authors refer to changes in "kidney function" relying on changes with time in estimated GFR (eGFR)!!!!!
When will nephrologists remember that changes in eGFR DO NOT equate solely to changes in RENAL FUNCTION....???
Instead, they equate to changes in serum creratinine levels.
When will Nephrologists remember that changes in serum CREATININE levels can be due to a number of non-renal factors??? including:
Muscle mass and Creatinine metabolism
When will Nephrologists relaise that a fall in creatinine, especially in the elderly, is a reflection of sarcopenia; itself associated with increased risk of death!
So rather than argue that a rising creatinine is bad news, they should have argued, or at least mentioned..., that a falling serum creatinine is bad news; WASTING and SARCOPENIA in the elderly increases risk of MORTALITY!
So the observation under discussion reminds me of the REVERSE EPIDEMIOLOGY observed in renal ESRD patients; serum: low potassium, low creatinine, low phosphorus are all predicotrs of higher mortality....due to MALNUTRITION and WASTING, so does low serum albumin!
The authors have merely extended these observation to an observed cohort showing that falling/declining serum creatinine levels are equally associated with higher mortality in people with CKD, mostly elderly.
Similar misrepresentations of eGFR are contaminating our literature.
One such example:
eGFR and progression of Alzeihmer's disease (AD); nothing to do with eGFR but instead all to do with falling LEAN BODY MASS (LBM)!
"....Individuals with AD demonstrated a paradoxical finding in which lower baseline MDRD eGFR (HIGHER SERUM CREATININE) was associated with less cognitive decline and brain atrophy, a phenomenon not observed in non-AD controls.Those with lower eGFR had HIGHER LBM; in other words, less wasted and sarcopenic...."
Therefore accounting for LEAN BODY MASS would significantly mitigate the misinterpretation of such observations including that relating to mortality with higher eGFR.
It is high time that Nephrologists remember and dont forget that eGFR DOES NOT EQUATE TO MEASURED GFR!
That eGFR is an unsuitable tool to measure renal function in those with declining muscle mass!