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Rev Electron Biomed / Electron J Biomed 2016;1:.
THE AGEING KIDNEY: A PROPOSAL FOR ITS CLASSIFICATION
Carlos G. Musso MD. PhD., 1,2
José R. Jáuregui MD. PhD.2
1Servicio de Nefrología y 2Unidad de Biología del Envejecimiento
Hospital Italiano de Buenos Aires. Argentina.
Version en español
Renal senescence is characterized by a set of capabilities usually altered by ageing, such as a reduced glomerular filtration rate (GFR), free water clearance, potassium secretion, as well as sodium and water reabsorption1. However, renal senescence is clearly a different process from chronic renal disease since the aged kidney, conversely to chronic nephropathy, presents a GFR reduction without abnormal values neither in serum urea and creatinine levels, urinalysis (except for proteinuria < 0.3 gram/day), nor renal imaging (except for a slightly reduced kidney size and /or isolated cysts) 2.
Moreover, glomerular filtration reduction induced by ageing shows a particular rate since it reduces around 1 ml/year since 40 years of age, a phenomenon which is not so predictable in chronic kidney disease 1. In this sense, Keller et al. have described a practical equation for determining the expected GFR reduction related to the age (GFR: 130 - age), which is conceptually quite different from the classical estimating GFR equations3-4.
Nevertheless, it is worth pointing out that kidney senescence leads to a need of adjusting medication doses, as well as to an increased risk for developing acute renal failure; being these phenomena even more significant in the oldest old (age > 80 years) 5-6.
Because of all mentioned above, we proposed to consider the aged kidney as a particular entity (kidney senility) different from the young kidney and the CKD, as well as to classify kidney senility (KS) in three levels (based on different GFR levels obtained by applying BIS1 equation, since it is the only GFR equation validated in the elderly 7-8 (Figure 1):
- Level I (successful KS): an elderly (age > 65 years old) with a GFR > 65 ml/min/1.72 m2 (BIS1 equation) in a context of a preserved renal reserve (at least 20% of renal reserve), since its absence in a context of relative high GFR would mean the presence of hyperfiltration, and consequently renal disease.
- Level II: an old individual (age 65-79 years old) with a GFR between 65-50 ml/min/1.72 m2 (BIS1 equation).
- Level III: a very old individual (age > 80 years old) with a GFR between 49-30 ml/min/1.72 m2 (BIS1 equation).
We consider that this originally proposed classification in different renal functional levels in the healthy elderly, which is based on gerontological and renal physiological concepts, could help to establish a common language among physicians who assist elderly patients, and/or investigate the renal senescence process
1.- Macías-Núñez JF, López-Novoa JM. Physiology of the healthy aging kidney. In Macías-Núñez JF, Cameron S, Oreopoulos D (Eds.) The aging kidney in health and disease. New York. Springer. 2008: 93-111
2.- Musso CG, Jauregui JR. How to differentiate renal senescence from chronic kidney disease in clinical practice. Postgrad Med. 2016 Jul 21:1-6.
3.- Keller F.Kidney function and age. Nephrol Dial Transplant. 1987;2(5):382
4.- Musso CG, Álvarez-Gregori J, Jauregui J, Macías-Núñez JF. Glomerular filtration rate equations: a comprehensive review. Int Urol Nephrol. 2016 Jul;48(7):1105-10.
5.- Domínguez-Gil Hurlé A, García-Sánchez MJ, Fernandez De Gatta MM, Sanchez-Navarro A. Pharmacokinetics in geriatric population. In Macías-Núñez JF, Cameron S, Oreopoulos D (Eds.). The aging kidney in health and disease. New York. Springer. 2008: 481-493
6.- Musso CG, Liakopoulos V, Ioannidis I, Eleftheriadis T, Stefanidis I. Acute renal failure in the elderly: particular characteristics. Int Urol Nephrol. 2006;38(3-4):787-93.
7.- Schaeffner ES, Ebert N, Delanaye P, Frei U, Gaedeke J, Jakob O, Kuhlmann MK, Schuchardt M, Tölle M, Ziebig R, van der Giet M, Martus P. Two novel equations to estimate kidney function in persons aged 70 years or older. Ann Intern Med. 2012; 157(7):471-478
8.- Musso CG, Reynaldi J, Martinez B, Pierángelo A, Vilas M, Algranati L.
Renal reserve in the oldest old. Int Urol Nephrol. 2011 Mar;43(1):253-6.
Carlos G. Musso
Departamento de Investigación.
Hospital Italiano de Buenos Aires.
carlos.musso @ hospitalitaliano.org.ar