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      Need for a nomogram of renal sizes in the Indian population

      The Indian Journal of Medical Research

      Medknow Publications & Media Pvt Ltd

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          Abstract

          The determination of normal renal size in any population is important in the diagnosis, treatment and prognosis of renal disease1. Renal size estimation can be performed measuring renal length, renal volume, cortical thickness or volume. The most accurate of these parameters is renal volume2 3, as the shape of kidney varies considerably. Renal length is, however, the most clinically useful parameter, due to its low inter-observer variation and better reproducibility2. Different imaging modalities such as conventional radiographs, intravenous urography (IVU), ultrasound (US), computerized tomography (CT) and magnetic resonance imaging (MRI) have been used to estimate renal size. However, the most accurate of these modalities are the MRI and CT, because these can acquire three-dimensional data and, therefore, do not rely on geometric assumption to estimate organ volume unlike the ultrasonography that is used to measure kidney size in two dimensional nature3. The use of CT as a routine non invasive method to estimate renal size is limited by the need for ionizing radiation and potentially nephrotoxic contrast media. Conversely, MRI has the benefit of acquiring true tomographic data along any orientation without constraints of ionizing radiation and nephrotoxic burden3. It is however, very expensive and not readily available especially in the rural and semi-urban areas where majority of population resides. Ultrasound is also known to underestimate renal size by about 20-29 per cent, while MRI underestimates it by about 4-5 per cent3. In spite of its shortcoming, renal size estimation using US is still a safe, simple and non invasive method with many advantages over other imaging modalities. These advantages include usage of non ionizing radiation, little or no patient preparation and no medication or injection of contrast media. It is also readily available, less expensive and easily reproducible to a large extent4. It should also be noted that renal dimensions measured by using US are smaller than those obtained by using radiography, because no geometric magnification and osmotic diueresis caused by intravenous contrast medium occurs5. Thus, the use of US by Muthusami and colleagues6 is a good approach as a portable US machine can be made readily available in the nooks and cranny of Indian subcontinent, whenever a large scale study is to be carried out. This cross-sectional study used patients referred for ultrasound examination for non-renal indications; this could have introduced a major selection bias. Since it is a study that was intended to assess the trends and collect preliminary data in healthy Indian adults6, it would have been better to recruit the subjects from the community and in population with no apparent medical conditions and optimal renal status based on calculated estimated glomerular filtration rate (eGFR) using serum creatinine as done in other studies1 7. It is a well known fact that abnormalities of kidney size are present in many renal diseases. Kidney size using either renal length or volume as a unit of measurement, is an important clinical parameter in the evaluation and follow up of kidney transplant patients8 9. It is, therefore, valuable to have a set of standard sonographic measurements to use when these patients are examined in a given population7, these seems to be lacking in the Indian population as stated by the authors of this study6. The measured parameters used in this study6 have been shown by many authors to be a good indicator of kidney weight and volume as well as its functional state, it is for this reason that longitudinal axis of the kidney is used as a reliable parameter during clinical examination10 11 12 13 14 15 16 17. The data from the study have justified the need for a nomogram in Indian population, this could be gleaned from the range of values of renal length determined in this study, in which some individual who are “healthy” may be having renal length of less than 9 cm that is widely acceptable as a cut-off to indicate irreversible renal damage in many populations18. The result of this study also showed that the mean renal length in an Indian population was smaller than the Caucasians, Brazilians, Korean and Japanese population, but closer to values in the Pakistanis, Malaysians, Nigerians and Jamaicans. The reasons for this was ascribed to be due to difference in height, weight, BSA, BMI and other anthropometric measurements among races. The authors have shown a positive correlation between renal length and weight, height and BMI6, and this has been corroborated by other study19. The authors also raised a valid point for a need to assess the possibility of racial differences of renal dimensions independent of body sizes, as they found that the renal dimensions in Indian population were smaller than the other races of smaller built such as the Pakistanis, Koreans, Iranians and Japanese compared to the Caucasians, normally of big stature. It was worthy to note that no significant differences were found between the mean left and right renal lengths or gender dependent differences6. It is well established by several studies1 2 4 18 20 21 22 23 that the mean left kidney length is more than the right kidney length and female kidneys are usually smaller in size when compared to that of males. Studies have shown that renal length gradually decreases as age advances and this decrease accelerates after the seventh decade of life23. The findings of muthusami et al 6 also agree with this, as there was significant decline in bilateral renal length after the age of sixty years. The explanation is that the number of nephrons per normal kidney which varies between 400,000 and 1,000,000, diminishes with advancing age and sex24. The data from the study in this issue6 have demonstrated the need for a nomogram in Indian population, as knowledge of normal kidney dimensions is valuable for accurate assessment of the abnormal kidney25. However, it is advisable that healthy individuals from the community are to be studied instead of hospital patients without apparent renal impairment. The paucity of data on this topic in the Indian subcontinent makes it imperative for this study to be carried out on a large scale.

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          Most cited references 31

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          Glomerular number and size in relation to age, kidney weight, and body surface in normal man.

          The number and size of glomeruli in normal, mature human kidneys were estimated by a direct and unbiased stereological method, the fractionator. The number was 617,000 on average, and the mean size 6.0 M microns3. Both glomerular number and size showed significant negative correlation to age and significant positive correlation to kidney weight. Apparently, humans loose glomeruli with age. Body surface area correlated positively to kidney weight and total glomerular volume but not to number of glomeruli. Body surface area correlates significantly with metabolic rate (Robertson and Reid, Lancet, 1: 940-943, 1952). Thus, intraspecies adaptation of kidney filtration capacity to the metabolic demand is performed by changing the size of glomeruli, i.e., the number of glomeruli in individuals of a given species is independent of the metabolic rate.
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            Normal values for renal length and volume as measured by magnetic resonance imaging.

            The objective of this magnetic resonance imaging (MRI) study was to (1) test the validity of the ellipsoid formula for estimating kidney volume using ex vivo and in vivo models and (2) establish a normal range of values for kidney length and volume in patients with no known history of renal disease. The volumes of five excised porcine kidneys were measured by (1) disc-summation method, (2) ellipsoid formula, and (3) water displacement method. In a retrospective, consecutive group of clinically referred patients (n = 150; 300 kidneys), individual kidney volume and length were calculated by the disc-summation method and by multiplanar reformation of MRI data, respectively. For comparison, kidney volumes also were calculated using the ellipsoid formula in all patients. Renal volume that was obtained by MRI using the disc-summation method was within 5% of the volume that was determined by the water displacement method, independent of the spatial resolution of the MRI technique used. Data from both the in vivo and the ex vivo models revealed that the ellipsoid formula that commonly is used in ultrasonography underestimates renal volume by 17 to 29% compared with the disc-summation method (P < 0.05). As measured by MRI (mean +/- SD), kidney lengths were 12.4 +/- 0.9 cm for men and 11.6 +/- 1.1 cm for women, and kidney volumes were 202 +/- 36 ml for men and 154 +/- 33 ml for women. The results from the ex vivo MRI study show that the kidney volume that was obtained using the disc-summation method is within 5% of the true kidney volume as measured by the water displacement method. The ellipsoid formula consistently and significantly underestimates the true kidney volume. The length and the volume of kidneys that are obtained by MRI in patients with no known history of intrinsic renal disease are greater than the commonly quoted reference values that are obtained by ultrasonography.
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              Intraobserver and interobserver variations in sonographic measurements of kidney size in adult volunteers. A comparison of linear measurements and volumetric estimates.

              Estimation of renal size by sonography can be performed by measuring renal length, volume, cortical volume or cortical thickness. Observer variation in these measurements is an important factor, especially when repeated measurements are compared. This study was performed to examine the magnitude of intraobserver and interobserver variations for each of the above-mentioned measurements, and to find the measurement with the lowest observer variation. Sonographic measurements were performed by 3 observers on 18 adult volunteers. The standard deviation of the difference (SDD) between any 2 pairs of measurements was used as the indicator of the magnitude of the observer variation. Renal length measurement showed the lowest observer variation with a relative SDD of 4 to 5%. Measurement of cortical thickness showed the poorest reproducibility with a relative SDD of 18 to 23%, while volumetric estimations had a relative SDD of 14 to 17%. Renal length measurement should be preferred to renal volume estimation, especially when comparing repeated measurements.
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                Author and article information

                Journal
                Indian J Med Res
                Indian J. Med. Res
                IJMR
                The Indian Journal of Medical Research
                Medknow Publications & Media Pvt Ltd (India )
                0971-5916
                0975-9174
                May 2014
                : 139
                : 5
                : 663-665
                Affiliations
                Department of Radiology, Federal Medical Centre, Owo, Ondo State, Nigeria deji_egbe@ 123456yahoo.com
                IJMR-139-663
                4140029
                Copyright: © Indian Journal of Medical Research

                This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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