Weight of the Human Kidney – A Study on 70 Autopsy Cases

Background: Variations in weight of the kidney in different populations and in different age groups are evident. Objective: The aim of the present study was to find out age related changes in weight of the kidney in a Bangladeshi population and compare with previous local and foreign studies. Materials and method: This cross-sectional study was done in the Department of Anatomy, Dhaka Medical College, Dhaka, Bangladesh from July 2008 to June 2009, based on collection of 140 post mortem human kidneys collected from 70 unclaimed dead bodies which were in the morgue under examination in the Department of Forensic Medicine of same institute. All the samples were divided into three different age groups A (10-19 years), B (20-39 years) and C (40-59 years), and the weight of each kidney was measured by using a digital balance and recorded. Results: The weight of the right and left kidneys were found 86.18±0.32 gm and 86.10±0.10 gm in group A, 102.25±7.64 gm and 101.96±7.27 gm in group B, 95.59±0.75 gm and 95.19±1.24 gm in group C respectively. No difference was found between the right and left kidneys in any group. However, statistically significant differences were evident among age groups. Conclusion: The weight of the kidney was found to increase up to 4th decade of life and then declined with further advancing age.


Introduction
The kidney hosts dramatic alterations in its structure and functions with advancing age including a profound reduction of its weight. 1 The kidney is characterized by the intensive processes of maturation, but also by changes of involution.
These processes begin during the fetal life when predominate the process of maturation and some changes of involution, and continue after birth.After birth there is a process of the structural maturation of the kidney; it reaches its full Assistant Professor of Anatomy, OSD, Directorate General of Health Services (DGHS), Dhaka, Bangladesh.Assistant Professor of Anatomy, OSD, Directorate General of Health Services (DGHS), Dhaka, Bangladesh.Associate Professor, Dept. of Anatomy, Ibn Sina Medical College, Dhaka, Bangladesh.anatomical maturity by the third-fourth decade of life. 2,3From there on the human kidney is characterized by the changes of involution.These changes of involution are found in all anatomical segments of the kidney and initially they are slow but after the end of sixth decade they are more rapid in progression. 2,4The changes of involution can be separate, but they can coincide with renal diseases. 2,5However, studies also revealed that age, sex, and race had no additional impact on kidney weight except body built i.e. body surface area. 6Hence, the population based study has become a field of interest for the researchers who are working on morphological changes in aging kidney and its functional correlation.Moreover, it has been observed by various researchers that the dimensions of different organs in Bangladeshi population have got variations from those of the western population. 7Hence, the present study was designed to see the variations in weight of kidney with increasing age in a Bangladeshi population and to compare with previous local and foreign studies.

Materials and method
This cross-sectional study was done in the Department of Anatomy, Dhaka Medical College, Dhaka, Bangladesh from July 2008 to June 2009, based on collection of 140 post mortem human kidneys collected from 70 unclaimed dead bodies which were in the morgue under examination in the Department of Forensic Medicine of the same institute.All the samples were collected from medicolegal cases excluding poisoning, any cutting or crushing injury to the kidneys, kidney found in one side or grossly abnormal in shape/size and from patients suffering from any kidney disease.For convenient description of changes in weight of the kidney in relation to age, the collected samples were divided into three age groups including A (10-19 years), B (20-39 years) and C (40-59 years), according to Darmady et al. 8 (Table I).The kidney was taken and its outer surface was dried with blotting paper.Then it was weighed by means of a digital balance (SCIENTECH ZSA 210, made in USA) in grams.
All data were recorded and processed.The comparison of weight of kidneys between right and left side was done by unpaired Student's't' test and the comparison of between different groups was done by One-way ANOVA.All the statistical analyses were done by using SPSS, version 13.0 for Windows.This study was approved by the Ethical Review Committee of Dhaka Medical College, Dhaka, Bangladesh.

Results
The weight of the right and left kidneys were found 86.18±0.32gm and 86.10±0.10gm in group A (10-19 years), 102.25±7.64gm and 101.96±7.27gm in group B (20-39 years), 95.59±0.75gm and 95.19±1.24gm in group C (40-59 years) (Table II).No significant difference was found between the weight of right and left kidneys in any group.However, statistically significant differences were evident for weight of kidney of each side among all age groups (Table II).However, some studies have other mathematical results than ours, but they reveal also the changes of kidney at different ages. Molina & DiMaio 19 studied on 232 male subjects, aged 18-35 years, and found the mean weight of the right kidney was 129 gm (ranged from 79 to 223 gm), and that of the left kidney was 137 gm (ranged from 74 to 235 gm).However, they proposed a reference value for male organ's weight as for right kidney 81-160 gm, and left kidney 83-176 gm.Apart from few exceptions, the results of the present study are similar to the previous records.The variations of kidney weight between Bangladeshi and western people might be because of higher body weight as well as greater body surface area in western population. 16In the course of aging, reduction of kidney weight is evident as there is a progressive loss of renal parenchyma i.e. one third to one half of renal nephrons is lost by old age. 4

Conclusion
The weight of the kidney was found to increase up to 4th decade of life and then declined with further advancing age.The results of the present study can be used as a standard reference weight for the kidneys of Bangladeshi people and to determine the abnormal evidences in forensic and pathologic corpses.Further studies with lager samples and comparison between sexes are recommended.
Associate Professor, Dept. of Anatomy, East-West Medical College, Dhaka, Bangladesh.Associate Professor, Dept. of Anatomy, The Medical College for Women & Hospital, Uttara, Dhaka, Bangladesh.Professor & Head, Dept. of Anatomy, Dhaka Medical College, Dhaka, Bangladesh.

Table II : Weight of right and left kidney in different age group
Figures in the parenthesesindicate range.Comparison between right and left side done by unpaired Student's 't' test and comparison between different age groups done by One-way ANOVA (PostHoc).ns = not significant, *** = significant.