Introduction
Ultrasound (US) measurements of kidney dimensions are crucial for establishing correlations with height, weight, and body mass index (BMI) and setting baselines for normal kidney sizes, thus providing insights into healthy parameters for this vital organ [1, 2]. Ultrasound technology is a valuable tool for visualizing internal body structures, offering a safe, cost-effective and noninvasive imaging technique that provides detailed data on the kidneys and other vital organs [3–7]. Kidney dimensions serve as indicators of declining kidney function and tissue loss [8, 9]. Given that many kidney disorders involve size fluctuations, guidelines for measuring kidneys have been established and are widely used in clinical settings. Establishing baseline estimations of typical kidney size under healthy conditions is essential [8, 9].
The global prevalence of overweight and obesity has increased awareness of the connections between various health conditions and BMI, including chronic kidney disease [10–12]. BMI, a simple, low-cost, noninvasive measure of body fat, allows individuals to monitor their BMI regularly, contributing to its utility at the population level [13–15]. BMI is calculated by dividing weight (kg) by height squared (m2) and is used to classify individuals according to their degree of obesity [14–16]. A BMI of less than 18.5 is classified as underweight; 18.5–24.9 is normal; 25–29.9 is overweight; and 30 or higher is obese [16, 17]. In recent years, the rapid increase in obesity rates worldwide has become strikingly evident [18–22]. Obesity is associated with increased mortality risk and is linked to chronic kidney disease (CKD) [18].
In a comprehensive study of renal dimensions, Amirkhanlou et al. analyzed kidney lengths in 320 individuals with a mean age of 48.03 ±14.86 years [1]. The results revealed notable differences in kidney size, with the right kidney averaging 113.27 ±8.57 mm in length and the left kidney averaging 111.91 ±9.199 mm. These dimensions were distinct when compared to those reported for Kuwaiti [23], Mexican [24], and Nigerian populations [25], which recorded lengths of 106.7 ±14 mm, 100 ±7 mm, and 103 ±17 mm, respectively. Additionally, Amirkhanlou et al. observed gender differences, noting that males had higher BMI, height, and right kidney length than females [1].
El-Reshaid and Abdul-Fattah conducted a study to establish normal renal size parameters via ultrasound in individuals without renal disease [23]. They examined 252 healthy participants (111 males and 141 females) aged 18–80 years, categorized into five age groups. The mean right and left renal lengths in the Kuwaiti population were 10.68 ±1.4 cm and 10.71 ±1.0 cm, respectively. A significant correlation between renal length and body weight was observed, with an increase of 0.23 cm in renal length for every 10 kg increase in body weight within the 60–120 kg range. However, no statistical correlation with height was found. The research further revealed a notable correlation between BMI and renal length, yet found no significant gender-based disparities in overall renal length. Additionally, a reference chart was created for the Kuwaiti population, depicting standard values for renal length and cortical thickness within a 95% confidence interval.
Oyuela-Carrasco et al. highlighted the importance of ultrasound-based renal length estimation as a replacement for radiography in evaluating adult patients with kidney disease [24]. In their prospective observational study of 153 healthy volunteers, including 77 males and 76 females with an average age of 46.12 ±15.44 years, significant anthropometric measurements were reported. The study found higher average right and left renal lengths in males, measuring 105.74 ±5.74 mm and 107.16 ±6.97 mm, respectively. A positive correlation was identified between renal length and weight, BMI, and height [24, 25].
This study investigates the potential relationship between renal dimensions and height, weight, and BMI in Saudis, aiming to understand how variations in these parameters influence kidney size.
Material and methods
Design and settings
This observational cross-sectional study was conducted over 9 months, from September 2023 to June 2024, at two ultrasound clinics in Riyadh, Saudi Arabia. The objective was to investigate the relationships between renal dimensions and the anthropometric measures of weight, height, and BMI in individuals aged 18 years and older.
The study cohort comprised 129 participants, including 73 males and 56 females. Height was measured in centimeters and converted to meters, while weight was recorded in kilograms. BMI was calculated using the formula: BMI = weight (kg)/height (m)².
Ultrasound scans were performed on all participants using SonixTouch and Philips machines, each located at one of the clinics, and equipped with low-frequency curvilinear transducer probes (2–5 MHz). Renal dimensions, including the longest longitudinal diameter (bipolar axis), width, and cortical thickness (defined as the distance from the outer border of the renal cortex to the outer border of the medullary pyramid), were measured in millimeters for both kidneys, as illustrated in Figure 1. The supine position was primarily utilized for these measurements, with right and left lateral decubitus positions adopted when necessary. Data collection was efficiently conducted using a comprehensive data collection sheet.
Statistical analysis
All statistical analyses were conducted using Python (version 3.10) [26] in the Google Colab environment. Normality checks were performed using the Shapiro-Wilk test. Given the non-normal distribution of the data, non-parametric tests were employed. The Spearman correlation coefficient was used to investigate the relationship between each kidney dimension and height, weight, BMI, and age. The Mann-Whitney U test was utilized to compare kidney dimensions between males and females.
Results
Participants’ demographics and characteristics
A total of 129 participants were included in this study, consisting of 73 (57%) males and 56 (43%) females. The age distribution of the participants ranged from 18 to over 60 years, with the majority (65%) falling within the 18-24 age group. Detailed demographic characteristics are presented in Table I.
Table I
Distribution of participants according to gender and age
| Gender | Number of participants | Percentage |
|---|---|---|
| Female | 56 | 43 |
| Male | 73 | 57 |
| Total | 129 | 100 |
| Age groups | Number of participants | Percentage |
| 18–24 | 84 | 65 |
| 25–30 | 9 | 7 |
| 31–40 | 16 | 12 |
| 41–50 | 12 | 9 |
| 51–60 | 6 | 5 |
| > 60 | 2 | 2 |
| Total | 129 | 100 |
The average age of the participants was 28 ±11 years. The average height, weight, and BMI were 1.66 ±0.10 m, 72.4 ±19.1 kg, and 26.3 ±6.1 kg/m², respectively.
Kidney dimensions
The average dimensions of the right and left kidneys for all participants are summarized in Table II.
Correlation analysis
Correlation with age
Age showed a significant negative correlation with kidney thickness for both kidneys. Specifically, the Spearman’s rank correlation coefficient for the right kidney thickness was –0.502 (p < 0.0001), and for the left kidney thickness, it was -0.542 (p < 0.0001). Additionally, age had a negative correlation with the left kidney width (r = –0.204, p = 0.020).
Correlation with height
Height showed a significant positive correlation with all measured kidney dimensions. For the right kidney, the correlation coefficients were 0.190 (length), 0.227 (width), and 0.651 (thickness). For the left kidney, the coefficients were 0.222 (length), 0.249 (width), and 0.635 (thickness). All correlations were statistically significant (p < 0.05).
Correlation with weight
Weight was also positively correlated with kidney dimensions. The right kidney dimensions had correlation coefficients of 0.284 (length), 0.389 (width), and 0.395 (thickness), while the left kidney dimensions had coefficients of 0.283 (length), 0.216 (width), and 0.351 (thickness). These correlations were statistically significant (p < 0.05).
Correlation with BMI
BMI was positively correlated with kidney dimensions, particularly with length and width. The correlation coefficients for the right kidney were 0.219 (length), 0.319 (width), and 0.090 (thickness). For the left kidney, the coefficients were 0.209 (length), 0.068 (width), and 0.044 (thickness). The correlation between BMI and kidney length and width was significant (p < 0.05). Detailed correlation coefficients and p-values are provided in Table III.
Table III
Correlation coefficients (r) and p-values of Spearman’s rank correlation test
Gender differences
The Mann-Whitney U test was used to compare kidney dimensions between males and females. Significant differences were found in kidney thickness, with males having greater thickness compared to females (p < 0.0001 for both kidneys). There was also a significant difference in the width of the left kidney (p = 0.0012), with males having wider kidneys (Table IV).
Table IV
Kidney dimensions by gender
Discussion
This study aimed to explore the relationships between renal dimensions (length, width, and thickness) and various anthropometric measures, including height, weight, and BMI, among a Saudi population. The findings highlight significant correlations between these anthropometric variables and renal dimensions, with distinct patterns emerging across different demographic groups (please refer to the heatmap in Figure 2).
Figure 2
Correlation coefficients (r) between kidney dimensions (length, width, and thickness) and various variables (age, height, weight, and BMI) for both right and left kidneys
Age demonstrated a notable negative correlation with kidney thickness for both kidneys. Specifically, as age increased, the thickness of both the right and left kidneys decreased significantly. This observation aligns with previous studies, such as those by Piras et al., which reported age-related reductions in renal size and cortical thickness, potentially due to age-related nephron loss and renal atrophy [9]. Additionally, the slight decrease in the left kidney’s width with age further supports the hypothesis of progressive renal structural changes associated with aging [9].
Height was positively correlated with all measured kidney dimensions. Taller individuals exhibited larger renal dimensions in terms of length, width, and thickness. This finding aligns with the study conducted by Oyuela-Carrasco et al., which also found positive associations between height and kidney size [24]. However, El-Reshaid and Abdul-Fattah found no significant correlation between height and renal length in their Kuwaiti population study [23]. This discrepancy may be due to differences in the populations studied or variations in measurement techniques. While El-Reshaid and Abdul-Fattah did not find a significant correlation between height and renal length, our study observed a positive correlation, which could be attributed to specific demographic and genetic factors present in the Saudi population.
Both weight and BMI were positively correlated with kidney dimensions. Heavier individuals and those with higher BMI had larger renal dimensions, particularly in terms of length and width. This relationship underscores the impact of increased body mass on renal size. Previous research, such as that by García-Carro et al. [18], has highlighted the link between obesity and increased kidney size, which may be attributed to hyperfiltration and compensatory hypertrophy in response to increased metabolic demands.
The analysis of gender differences revealed that males generally had greater kidney thickness compared to females. There was also a significant difference in the width of the left kidney, with males having wider kidneys. These findings align with the results of Amirkhanlou et al., who reported that males typically have larger renal dimensions due to differences in body composition and hormonal influences [1]. The greater kidney size in males may reflect higher muscle mass and larger body surface area, necessitating larger renal structures to support metabolic needs.
Implications for clinical practice
The observed correlations between anthropometric measures and renal dimensions have several clinical implications. Firstly, understanding these relationships can aid in the development of more accurate reference ranges for kidney size based on patient demographics. This is particularly important for the early detection and monitoring of renal diseases, as deviations from expected renal dimensions may signal underlying pathology.
Additionally, the findings emphasize the importance of considering patient-specific factors, such as age, height, weight, and BMI, when interpreting renal ultrasound measurements. Personalized assessment of kidney size can improve diagnostic accuracy and facilitate early intervention in cases of renal abnormalities.
Limitations
Despite the significant findings, this study has several limitations that should be acknowledged. The cross-sectional design limits the ability to establish causality between anthropometric variables and renal dimensions. Longitudinal studies are needed to confirm the observed associations and to elucidate the underlying mechanisms driving these relationships
Additionally, the reliance on ultrasound measurements, while non-invasive and widely accessible, may introduce variability due to operator dependency and the inherent limitations of ultrasound imaging. Standardizing measurement protocols and employing advanced imaging techniques could mitigate these issues in future studies.
Future research directions
Building on the findings of this study, future research should explore several key areas. Longitudinal studies that track changes in renal dimensions over time in relation to anthropometric changes would provide valuable insights into the dynamic nature of these relationships. Additionally, investigating the impact of other factors, such as diet, physical activity, and genetic predispositions, on kidney size could further elucidate the complex interactions influencing renal dimensions.
Moreover, expanding the study to include diverse populations across different regions and ethnic backgrounds would enhance the understanding of how demographic and environmental factors contribute to variations in kidney size. Such research could inform the development of tailored clinical guidelines for renal assessment in diverse patient populations.
In conclusion, this study establishes significant correlations between renal dimensions and anthropometric measures, underscoring the importance of considering individual patient characteristics in renal assessments. These findings provide a foundation for future research and underscore the potential for personalized clinical guidelines to improve the early detection and management of renal conditions. By advancing our understanding of these relationships, healthcare providers can enhance patient care and outcomes in the context of renal health.
Conclusions
This study aimed to investigate the relationships between renal dimensions and various anthropometric measures, including age, height, weight, and BMI, within a Saudi population. The findings have elucidated significant correlations that provide valuable insights into how these factors influence kidney size.
Age and kidney thickness: There is a significant negative correlation between age and kidney thickness for both the right and left kidneys. As individuals age, the thickness of their kidneys tends to decrease. This finding is consistent with previous research suggesting age-related nephron loss and renal atrophy.
Height and kidney dimensions: Height is positively correlated with all measured kidney dimensions. Taller individuals exhibit larger kidneys in terms of length, width, and thickness. This correlation underscores the physiological necessity for larger organs in taller individuals to maintain metabolic balance.
Weight and BMI: Both weight and BMI show positive correlations with kidney dimensions. Heavier individuals and those with higher BMI have larger kidneys, particularly in length and width. These findings are in line with the understanding that increased body mass imposes greater metabolic demands, leading to compensatory renal hypertrophy.
Gender differences: Significant differences were observed between males and females in terms of kidney thickness and left kidney width. Males generally had thicker and wider kidneys, which can be attributed to differences in body composition and hormonal influences.
