Introduction

Urolithiasis represents a considerable public health concern. Its global prevalence and incidence are increasing, especially in industrialized countries, where they have markedly risen in recent decades, exhibiting significant variation across race, gender, age, and geographic region (1, 2). The prevalence rates vary throughout the world, ranging from 7% to 13% in North America, 5% to 9% in Europe, and 1% to 5% in Asia (3).
Numerous risk factors influence the pathophysiology of urolithiasis, including age, male gender, environmental variables such as climate change and seasonal fluctuations, dietary habits, occupation, genetic predisposition, metabolic syndrome, obesity, diabetes, and hypertension (1). These risk factors along with associated diseases contribute directly or indirectly to the onset of hypercalciuria, hypocitraturia, low pH, hyperuricosuria, hyperoxaluria, cystinuria, and infections caused by urease-producing organisms, hence elevating the risk of acute urolithiasis (1).
The chemical makeup of urolithiasis is highly varied, ranging from more common calcium-containing stones (calcium oxalate, hydroxyapatite, or brushite) to the rarer uric acid, magnesium phosphate, and cysteine stones, making it impossible to anticipate overall trends based solely on risk factors (1).
The European Association of Urology (EAU) and American Urological Association (AUA) recommend stone composition analysis as part of the comprehensive assessment of patients with urolithiasis (4, 5).
There is a significant prevalence of stone disease (6). In Kenya, there is a lack of data specifically on the composition of urolithiasis. This study aimed to identify the sociodemographic and clinical characteristics, along with the composition of urinary stones, of patients presenting to our institution, emphasizing the importance of understanding urinary stone composition.

​

Materials and Methods

This research was performed at Kenyatta National Hospital (KNH), a tertiary and referral hospital in the capital city of Kenya. This facility oversees a diverse range of urological illnesses, including kidney stones, throughout the nation and the East African region. Ethical approval (P79/02/2025) was obtained from the Ethical Committee prior to the commencement of the project. This study was a retrospective cross-sectional review at KNH. The records of all patients diagnosed and surgically treated for urolithiasis from June 2023 to June 2024were collected.
The study population comprised all patients aged ≥13 years who underwent surgical management for urolithiasis and had a stone analysis report. Stone analysis was done by infrared spectroscopy from samples obtained during surgical management.
Patients who were managed medically, lacked stone analysis reports, and had inadequate data were excluded from the study. The study employed a non-probability consecutive sampling technique.
The sample size was calculated using Cochran’s formula shown below:

Formula
 
where n is the population size, P is the reported proportion of calcium oxalate stones (estimated at 93.5%) from a study by Undie et al. (2021) in Kelina Hospital, Abuja, Nigeria (7), q=1−P, e is the error margin (0.05), and Z is the statistic for the level of confidence [95% confidence interval (CI) with a Z value of 1.96].
Therefore,

Calculation

​

Hence, the desired sample was n=90 patients.

Following the acquisition of ethical approval, the physical files were accessed using the International Classification of Diseases code for urolithiasis. The collected data encompassed patient demographics (age, sex, occupation, and residence), clinical characteristics such as flank pain, fever, nausea, vomiting, and hematuria, as well as chemical stone composition. Data entry, coding, and analysis were conducted using Statistical Package for Social Sciences (SPSS) version 26. We employed means and SDs for the analysis of continuous numerical data, while frequencies and percentages were utilized for categorical data. Data were presented using bar graphs, pie charts, and frequency tables. A p value <0.05 indicated statistical significance, and a 95% CI was employed to assess this result.
​

Results

In our study, 218 patients with urolithiasis were identified, with 128 patients excluded; 121 were excluded due to medical management and 7 were excluded due to missing data. Ninety patients who underwent surgical management for urolithiasis and had a stone analysis report were included in the final study (Figure 1). Sixty-six (73.3%) patients were male (Figure 2).

 

Figure 1.

Flow chart.

 

Figure 2.

Gender distribution.

The average age was 35.8 years, with an SD of 6.7 years; the median age was 35 years, with an interquartile range of 32–39 years. The youngest patient diagnosed with urolithiasis was 20 years old, while the oldest was 59 years old. In an overall population of 90 urolithiasis patients, the predominant age group was 31–40 years, representing 58.9% (n=53) of patients (Figure 3).

 

Figure 3.

Distribution of age by gender.

The age distribution by gender in urolithiasis patients shows a significant male predominance, especially within the 31–40 age group, which constitutes 45.6% (n=41) of the overall sample. Females in the same age bracket constitute 13.3% (n=12), suggesting that males in their third and fourth decades are disproportionately impacted, as illustrated in Figure 3.
Flank pain emerged as the predominant clinical symptom, reported by 97.8% (n=88) of patients, followed by dysuria in 48.9% (n=44) of patients. Nausea and vomiting were each reported in 21.1% (n=19) of patients (Table 1).

 

Table 1.

Clinical characteristics by gender and age 
 

Male participants reported flank pain as the most common symptom (97.0%), followed by dysuria (47.0%) and nausea/vomiting (25.8%). Female subjects also reported high levels of flank ache (100.0%) and dysuria (54.2%). Dysuria and nausea/vomiting were most common in people aged 31–40 years (47.2% and 22.6%, respectively). There were no significant relationships between gender, age, and symptom distribution (p > 0.05), as shown in Table 1.
The findings showed that the majority had stones located in the upper urinary tract, accounting for 96.7% (n=87) of patients. Only 3.3% (n=3) presented with stones in the lower urinary tract.
The majority of urolithiasis patients had stones with heterogeneous compositions. Calcium oxalate was the predominant stone, with monohydrate (whewellite) present in 95.6% (n=86) of patients and dihydrate (weddellite) in 90.0% (n=81). Uric acid (uricite) was the second most prevalent component, found in 52.2% (n=47), followed by basic calcium phosphate (apatite) (Table 2).

 

Table 2.

Stone composition of urolithiasis patients

Calcium oxalate monohydrate (whewellite) and dihydrate (weddellite) were the predominant constituents of stones in both sexes. Uric acid (uricite) was more prevalent in males (58.6%) compared to females (37.5%), whereas struvite was more frequently observed in females (33.3%) than in males (16.7%).
Whewellite and weddellite were consistently prevalent throughout all age categories, with a 100% frequency in patients aged ≥41 years. Uricite and struvite were more prevalent during the fourth and fifth decades of life. No statistically significant correlations were detected between age and stone composition (p > 0.05), as shown in Table 3.

​

Table 3.

Stone composition by gender and age

​​

Discussion

The average age of 35.8 years observed in this study at KNH is notably younger than that reported in several comparable studies (8). For instance, Ngugi et al. reported a mean age of 44.8 years in Nairobi in 2010 (6). The age distribution observed in this study more closely resembles findings from Nigeria, where it was reported that stones were most common among patients aged 31–40 years (7). Collectively, these findings suggest that urolithiasis in Africa affects a younger demographic compared to industrialized nations, where the peak incidence occurs within the fifth decade of life (9, 10).
Flank pain was reported in nearly all patients (97.8%), which aligns with findings from other studies (11, 12). Wathigo et al. observed flank pain in 91% of patients in a multiethnic study in Nairobi (9). Dysuria (48.9%) and nausea or vomiting (21.1% each) were also frequent symptoms, reflecting regional patterns (13). The low rates of fever and microscopic hematuria indicate that most patients sought care before developing serious infections, which is advantageous for clinical management.
The overwhelming predominance of upper urinary tract stones (96.7%) is consistent with modern epidemiological trends in both developing and industrialized countries (7, 12, 14). Bladder stones were historically more prevalent, but kidney stones have become predominant over the past century (14). This shift has been attributed to improved nutrition, changing dietary patterns, and reduced rates of childhood malnutrition. The findings align closely with those of Dirie et al., who reported 93% of stones in the upper tract in Somalia (15), and with global patterns, where approximately 95% of stones occur in the upper tract (16). This finding suggests that Kenya may be experiencing the epidemiological transition seen in other developing nations, moving toward stone patterns typical of industrialized countries.
The predominance of calcium oxalate stones (whewellite 95.6%, weddellite 90.0%) situates Kenya within the global pattern observed in industrialized nations and indicates a significant epidemiological transition. This observation aligns with international data (10). Ye et al. reported 65.9% of calcium oxalate stones in China (17). The prevalence at our facility exceeds that of many developed countries, which may reflect the advanced westernization of dietary and lifestyle habits.
The high frequency of mixed stone compositions, with most stones containing multiple components, is typical of modern stone disease. The substantial presence of uric acid (52.2%) as a secondary component is noteworthy and higher than that reported in many Western series where uric acid typically comprises <20% of stones (10). This elevated uric acid content may reflect dietary patterns high in purines, environmental factors such as chronic dehydration, or genetic predispositions. Halinski et al. observed that uric acid stones are more prevalent in tropical climates, a factor pertinent to Nairobi’s equatorial position, despite its relatively highland temperatures and fluctuating dietary patterns (10).
The relatively low prevalence of struvite stones contrasts with historical patterns in developing countries. Daudon et al. reported struvite in 42.9% of stones in women in sub-Saharan Africa (18), while this study found much lower rates (33.3% in females, 16.7% in males as a component) (18). This reduction likely reflects improved sanitation, better treatment of urinary tract infections, and changing patterns of urinary pathogens. However, the persistence of struvite, particularly in females, indicates that infection-related stones remain a clinical concern.
The higher prevalence of uric acid stones in males is consistent with global patterns and likely reflects gender-based differences in dietary habits, body mass, and purine metabolism (17). The increased frequency of struvite stones in females (33.3% vs. 16.7%) corresponds with greater susceptibility of women to urinary tract infections attributable to anatomical factors. These observed gender differences underscore the need for targeted prevention strategies.
The consistent presence of whewellite and weddellite across all age groups, reaching 100% in patients aged ≥41 years, suggests that calcium oxalate stone formation is the dominant pathophysiological mechanism throughout adult life in our population. The increased frequency of uricite in the >50 age group (100%, though in a small sample) parallels findings from numerous studies showing age-related increases in uric acid stones (17). This may relate to age-associated changes in renal function, dietary patterns, medication use, or the development of metabolic conditions such as diabetes and hypertension.
The higher struvite prevalence in the 41–50 age group (37.5%) differs from some reports that show struvite to be more common in younger adult women or children (10). This finding may reflect the cumulative effects of recurrent urinary tract infections or specific risk factors in this population. The presence of less common components such as brushite, carbon apatite, and aragonite, though infrequent, demonstrates the heterogeneity of stone disease. The identification of these diverse components underscores the importance of comprehensive stone analysis in guiding metabolic evaluation and prevention strategies. The absence of statistically significant associations between age and stone composition should be interpreted cautiously, given the sample size, particularly in older age groups.
The retrospective design and dependence on pre-existing medical records limited the study due to potential issues with the completeness and accuracy of the documentation. Furthermore, the use of medical records retrospectively increases the possibility of documentation bias, particularly in relation to clinical symptoms. The study comprised 90 patients over a 1-year period, which, while noteworthy for a single-center experience, is still somewhat small. A small sample size may lower the study’s statistical power and capacity to detect rare adverse events or outcomes across subgroups. Exclusion of medically managed patients and those with incomplete or missing key information may have resulted in selection bias. We acknowledge that the lack of metabolic investigation data such as serum uric acid, urine calcium, oxalate, and citrate hinders the mechanistic interpretation of stone composition results. Excluded patients may have had distinct characteristics, which could bias the results toward more favorable findings. Despite the aforementioned limitations, our study elucidates the novel spectrum of stone composition within our population, and this information will be crucial in informing decision-making regarding the prevention and treatment of urolithiasis. A multi-center prospective cohort study is recommended to evaluate various risk factors for stone formation and composition.

​

Conclusion

Young adult males exhibited a higher incidence of urolithiasis than females. Flank pain was the predominant complaint, with the upper urinary tract being the most frequent site of occurrence. The majority of urolithiasis exhibited a heterogeneous composition. Despite a higher prevalence of uric acid stones in this study, oxalate stones continue to be the major cause of urolithiasis.

​

Author contributions

ENE led in conceptualization, data curation, formal analysis, funding acquisition, investigation and methodology. All authors equally contributed to project administration, resources, software, supervision, validation, visualization, and in writing, reviewing & editing of the original draft.

​

References

1. GBD 2021 Urolithiasis Collaborators. The global, regional, and national burden of urolithiasis in 204 countries and territories, 2000–2021: a systematic analysis for the Global Burden of Disease Study 2021. eClinicalMedicine. 2024; 78: 102924.

2. Xu LHR, Adams-Huet B, Poindexter JR, et al. Temporal changes in kidney stone composition and in risk factors predisposing to stone formation. J Urol. 2017; 197(6): 1465-71.

3. Sorokin I, Mamoulakis C, Miyazawa K, et al. Epidemiology of stone disease across the world. World J Urol. 2017; 35(9): 1301-20.

4. Skolarikos A, Somani B, Neisius A, et al. Metabolic evaluation and recurrence prevention for urinary stone patients: an EAU guidelines update. Eur Urol. 2024; 86(4): 343-63.

5. Pearle MS, Goldfarb DS, Assimos DG, et al. Medical management of kidney stones: AUA guideline. J Urol. 2014; 192(2): 316-24.

6. Ngugi PM, Magoha GA, Kiptoon D. Urolithiasis in Nairobi, Kenya. East Afr Med J. 2010; 87(10): 395-9.

7. Undie CU, Nnana EI, Torporo KR. Composition of Uroliths seen in patients in Abuja, Nigeria: a single centre retrospective analysis of 155 stones. Afr J Urol. 2021; 27(1): 91.

8. Diangienda PKD, Moningo DM, Ngoma A, et al. Urolithiasis management in resource-limited settings: a multicentric retrospective study in the Democratic Republic of Congo. Int J Innov Res Med Sci. 2023; 8(3): 85-90.

9. Wathigo FK, Hayombe A, Maina D. Urolithiasis analysis in a multiethnic population at a tertiary hospital in Nairobi, Kenya. BMC Res Notes. 2017; 10(1): 158.

10. Halinski A, Popov E, Bhattikam KH, et al. Kidney stone composition in various country around the world. 2021;93(3):307-312

11. Kassaw AB, Belete M, Assefa EM, et al. Prevalence and clinical patterns of urolithiasis in sub-saharan Africa: a systematic review and meta-analysis of observational studies. BMC Nephrol. 2024; 25(1): 334.

12. Mohammed S, Yohannes B, Tegegne A, et al. Urolithiasis: presentation and surgical outcome at a tertiary care hospital in Ethiopia. Res Rep Urol. 2020; 12: 623-31.

13. D.Andualem, G. Gidena. Admission-patterns-and-management-of-urolithiasis-a-hospital-based-study-in-Tikur-Anbessa-specialized-hospital-tash-Addis-Ababa-Ethiopia. ISSN 2073- 9990 East Cent. Afr. J. surg.   2014;19(3):6.

14. Cheng WY, Tseng JS. Urinary stone analysis and clinical characteristics of 496 patients in Taiwan. Sci Rep. 2024; 14(1): 14115.

15. Dirie NI, Adam MH, Garba B, et al. The prevalence of urolithiasis in subjects undergoing computer tomography in selected referral diagnostic centers in Mogadishu, Somalia. Front Public Health. 2023; 11: 1203640.

16. Wang B, Zheng X, Xiong J, et al. Characteristics of urinary stone composition among patients with urolithiasis: a retrospective study in China. BMJ Open. 2024; 14(11): e079431.

17. Ye Z, Zeng G, Yang H, et al. The status and characteristics of urinary stone composition in China. BJU Int. 2020; 125(6): 801-9.

18. Daudon M, Bounxouei B, Santa Cruz F, et al. [Composition of renal stones currently observed in non-industrialized countries]. Prog Urol. 2004; 14(6): 1151-61