Saudi Journal of Kidney Diseases and Transplantation

LETTER TO THE EDITOR
Year
: 2011  |  Volume : 22  |  Issue : 1  |  Page : 148--150

Free water clearance: Its behavior in chronic renal disease at different ages


CG Musso1, J Reynaldi1, B Martinez2, A Pierangelo1, C Mombelli1, M Vilas1, L Algranati1,  
1 Nephrology Division, Hospital Italiano de Buenos Aires, Argentina
2 Internal Medicine Division, Hospital Italiano de Buenos Aires, Argentina

Correspondence Address:
C G Musso
Nephrology Division, Hospital Italiano de Buenos Aires
Argentina




How to cite this article:
Musso C G, Reynaldi J, Martinez B, Pierangelo A, Mombelli C, Vilas M, Algranati L. Free water clearance: Its behavior in chronic renal disease at different ages.Saudi J Kidney Dis Transpl 2011;22:148-150


How to cite this URL:
Musso C G, Reynaldi J, Martinez B, Pierangelo A, Mombelli C, Vilas M, Algranati L. Free water clearance: Its behavior in chronic renal disease at different ages. Saudi J Kidney Dis Transpl [serial online] 2011 [cited 2019 Aug 21 ];22:148-150
Available from: http://www.sjkdt.org/text.asp?2011/22/1/148/74383


Full Text

To the Editor,

One of the known renal physiologic altera­tions described in Chronic Renal Disease (CRD) is a reduction in free water clearance (FWC). [1] It has also been described in the literature that there is a reduction of FWC in the healthy aged kidneys compared to the younger ones. [2] However, there are no reports describing whe­ther FWC is more reduced in the elderly CRD patients. Thus, we decided to conduct a pros­pective study in order to try and get an answer to the above-mentioned factor.

We studied FWC in 58 patients with CRD who were divided into four groups: 10 young patients (20-40 years) with CRD stage-2, 5 young patients (20-40 years) with CRD stage­3, 17 elderly patients (older than 64 years) with CRD stage-2 and 26 elderly (>64 years) patients with CRD stage-3.

Exclusion criteria included presence of car­diac failure, arrhythmia, hypothyroidism, cir­rhosis and use of non-steroidal anti-inflamma­tory drugs, diuretics and psycho-neurological medications.

All the studied patients were on a low protein diet (0.8 g/kg/day) and they underwent an oral water overload test which consisted of admi­nistering tap water (20 mL/kg) in 30 min and replacing each urinated volume by re-adminis­tering oral water. [2] During this 4-hour test, all the urine passed was collected for recording its volume and taking a sample for measuring creatinine and osmolality. Besides, four blood samples were drawn for measuring the same parameters. From the data thus collected, using the urine sample with the lowest osmolality (lower than 100 mOsm/L) and its correspon­ding blood sample, FWC was calculated ap­plying the following formula: [3] free water clearance = V - Osm Cl where

a) V = serum creatinine/urinary creatinine

b) osmolar clearance (Osm Cl) = (urinary osmolality/serum osmolality) × V%

c) V% = V × 100

All the study patients were pre-medicated with cimetidine (1600 mg/day) for 2 days before the evaluation. Besides, they also had a 2-week washout period free of angiotensin converting enzyme inhibitors and/or angiotensin receptor antagonists. In the above-mentioned blood and urine samples, creatinine was also measured and the creatinine clearance with cimetidine (a reliable glomerular filtration rate (GFR) mar­ker) was calculated from these data in each patient, applying the following formula: [4],[5],[6],[7] creatinine clearance with cimetidine = (urinary creatinine/serum creatinine) × [urinary volume (mL)/time (min)].

Student's "t" test was used for statistical analysis.

In our study, the GFR and FWC values were lower in both age groups compared to the standard ones in healthy people [Table 1] and [Table 2]. Besides, the GFR was significantly lower in the CRD stage-3 (old and young) groups com­pared to the CRD stage-2 groups (young and old). Conversely, there was no significant dif­ference in the GFR between young and old groups who belonged to the same stage of CRD [Table 1] and [Table 2].{Table 1}{Table 2}

Regarding FWC, even though there was no significant difference between young and old patients in the CRD stage-2 group [Table 1], there was a significant difference in this para­meter between young and old in the CRD stage­3 group [Table 2].

Under physiological conditions, free water excretion depends mainly on the GFR and the FWC. The former depends on the starling for­ces (hydrostatic and oncotic pressures) at both surfaces of the filtration barrier, as well as the barrier permeability and surface magnitude it­self, while the latter depends on sodium reab­sorption capability of the thick ascending loop of Henle. [4]

It is known that in CRD there are several tubular and glomerular structural and functio­nal alterations that result in a reduction in the free water excretion capability. Patients with CRD have damaged glomerular and tubular components, which determine renal free water excretion. [1] Besides, normal aging process also reduces free water excretion capability by in­ ducing glomerular and tubular changes, although they are of different nature when compared to the CRD patients: senile glomerulosclerosis and dysfunction of the thick ascending loop of Henle. [2] The latter is currently interpreted as a consequence of the reduction in the number of the sodium carriers (NaKCC2) in the apical surface of the thick ascending loop of Henle. [8] In our study, FWC was significantly lower in the elderly CRD stage-3 group compared to the younger group. This phenomenon could be explained by the conjunction of the advanced CRD and effect of the aging process.

In conclusion, our study shows that FWC was significantly reduced in the elderly CRD stage­3 patients, compared to the younger patients with the same stage of renal disease.

References

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