Changes in upper urinary tract stone composition in Australia over the past 30 years

Authors


Abstract

Objectives

  • To investigate upper urinary tract stone composition rates in Australia
  • To investigate changes in stone composition in Australia over the past 30 years

Patients and Methods

  • The Institute for Clinical Pathology and Medical Research (ICPMR) database was used to obtain – stone composition statistics from 2009–2011
  • Historical comparisons of stone composition rates were obtained from previous Australian studies; Rofe; 1981, and Baker; 1993 for epidemiological data from the 1970s and 1980s respectively.
  • Stone composition data was separated into gender and age-groups

Results

  • From the 791 stones analysed between 2009 and 2011, calcium oxalate remains the dominant type accounting for 64% of stones in our dataset, which compares to 68% from both the 1970s and 1980s.
  • Uric acid stones contributed 16% of contemporary stone compositions, comparable to 16% in the 1970s and 17% in the 1980s.
  • Struvite stones showed a decreasing trend from 14% in the 1970s, to 12% in the 1980s and 7% in the current data.
  • For struvite stones, while the female 21–30 age-group was the most prolific for struvite stone formation in the 1980s, the peak group in contemporaneous records is 61–70 year-old men.

Conclusion

  • Stone composition in Australia has remained relatively static over the past 30 years. Modifications in diet and body habitus have not resulted in significant changes in the proportion of uric acid and calcium oxalate stones detected.
  • The decreasing trend in the proportion of struvite stones most likely reflects improved management of urinary tract infections within the Australian population.

Introduction

Upper urinary tract stone disease remains a common health problem worldwide with significant morbidity. In Australia, the annual incidence of stone disease is estimated to affect 131 per 100,000 population [1]. Furthermore, in those with a history of upper urinary tract stones, studies have shown a recurrence rate of 50% within the subsequent 5–10 years [2].

Particular groups are more susceptible to stone formation with epidemiological data showing whites having higher rates than black populations and males having a 3x higher risk of stone disease compared to females [3]. The gender difference has always been at least partly attributed to differences in excretory function, with men excreting more oxalate in the urine, and women more citrate, which is protective against stone formation [2]. In addition, increased animal protein intake has been associated with higher rates of calcium oxalate stone formation, with a 5-year randomised trial revealing a protective effect of reduced animal protein and salt intake when compared with a low-calcium diet in recurrent stone formers [4]. Obesity has also been found to increase the risk of mixed calcium and uric acid stone formation, with one study showing increased BMI being associated with lower urinary pH and higher urinary uric acid, sodium and phosphate excretion [5].

Dietary advice and lifestyle modification are important for stone prevention, particularly in patients with calcium oxalate and uric acid stones. This long-held recommendation is supported by a 4-year study conducted on 45,619 males showing an inverse correlation between fluid intake and kidney stones, which was most pronounced in the quintile group consuming over 2.5L of fluid per day [6]. The theory of urine supersaturation being a cause of stone formation logically supports the protective effects of increasing urine volume with climatic factors also affecting urine solute concentrations. The contribution of climate has also been well researched in large epidemiological studies. Higher rates of stone disease have been found in a cross-sectional study of steel workers operating in hot-areas, and in a cross-over study involving military troops when moved from temperate to hotter climates [7, 8]. However, although the pathophysiology is clear of greater fluid losses in warmer climates contributing to reduced urine volumes and increased stone formation, strong causal evidence is still lacking due to the difficulty with controlling other variables [9].

The above factors of gender, genetics, climate, body habitus and diet have all been postulated to contribute to the formation of different stone composition types [10]. While some of these factors have changed over time, especially diet and body habitus, their effect on stone composition has not been investigated.

Aim

To investigate changes in stone composition in Australia over the past 30 years.

Method

The Institute for Clinical Pathology and Medical Research (ICPMR) database was used to obtain stone composition statistics from 2009 to 2011, which was separated by age and gender, and compared with historical Australian epidemiological studies by Rofe et al. [11] from the 1970s, and Baker et al. [12] from the 1980s.

Results

From the 791 stones analysed between 2009 and 2011, the vast majority were obtained following surgical management of urinary tract stones with only 11 documented analyses from stones that were spontaneously passed. Furthermore, only 15 stones were from patients who previously had stones analysed during the 3 years of data collection and in all of these cases, the stone type was identical across both analyses.

Calcium oxalate remains the dominant type accounting for 64% of stones in our dataset, which compares to 68% from both the 1970s and 1980s. The highest number of calcium oxalate stones was found in 51–60 year-old males; similar to historical findings by Rofe and Baker [11, 12] (Figure 1).

Figure 1.

Distribution of calcium oxalate stones with respect to age and gender.

Uric acid stones contributed 16% of contemporary stone compositions, comparable to findings of 16% in the 1970s and 17% in the 1980s by Rofe [11] and Baker [12] respectively. An obvious peak in uric acid stones was detected in males aged 61–70 in both recent and historical databases (Figure 2).

Figure 2.

Distribution of uric acid stones with respect to age and gender.

Struvite stones showed a decreasing trend from 14% in the 1970s [11], to 12% in the 1980s [12] and 7% in the current data. While the female 21–30 age-group was the most prolific for struvite stone formation in the 1980s, the peak group in contemporaneous records is 61–70 year-old men (Figure 3).

Figure 3.

Distribution of struvite stones with respect to age and gender.

Discussion

The similarity in percentage of uric acid and calcium oxalate stone types detected in the historical and current studies is remarkable. As expected, males have a higher rate of oxalate and uric acid stone formation in all age-groups. We did not detect a change in relative proportions of uric acid or calcium oxalate stone formation, despite the higher rates of protein consumption and obesity in contemporary society. Struvite stones were the only stone type to show a definite change since the 1970s. The loss of a peak group amongst younger women is possibly due to improved detection and treatment of urinary tract infections, however, the peak in older men is surprising given the increased rate of medical and surgical intervention in managing bladder outflow obstruction.

The current study has some limitations. In particular, not all stones were sent for analysis in our district over the 3-year period of investigation. Some patients pass stones spontaneously which go undetected, and others are not sent for analysis despite surgical removal. Our hope is that the proportion of these “lost” stones is experienced equally across the three stone types. Baker and Rofe do not comment about the completeness or otherwise of their sampling [11, 12]. Although stone composition changes offer implications for causation, this remains an observational study. The consistency in proportions of calcium oxalate and uric acid stones across gender and age groups over the past 30 years does not dismiss the potential effects of contemporary diet and metabolic changes on stone formation. These changes may impact equally across different stone types.

So what are the implications, if any, for urological practice? The value of investigating stone formers for metabolic disorders and the effectiveness of preventive strategies to reduce the risk of subsequent stone formation is under some dispute [13, 14]. Some patients would benefit from knowing the presence of metabolic conditions that would predispose them to upper urinary tract stones, however the usefulness of subjecting all first-time stone formers to a barrage of tests is debatable, since a large proportional of this group may not experience any subsequent symptomatic stone disease.

For all patients with upper urinary tract stones, the European Association of Urology (EAU) recommends thorough history taking to screen for those at risk of subsequent stone formation including familial cases, recurrent stones and early onset urolithiasis. Testing of stone composition in all patients is also recommended as well as urine dipstick and culture, and blood tests including blood cell count, creatinine, uric acid, electrolytes and CRP. Patients are subsequently stratified into high and low risk groups with metabolic evaluation reserved for those at high risk of recurrence. Metabolic investigations include serum calcium, uric acid and parathyroid hormone (PTH), and 24-hour urine collection x2, which is analysed for pH, specific weight, creatinine, calcium, oxalate, uric acid, citrate, magnesium, inorganic phosphate, ammonium and cystine [15].

Stone analysis is an important aspect of metabolic assessment, in first-time and recurrent stone formers. The stone composition detected essentially guides the type of investigations required and the appropriate management plan [16]. This is because determining stone composition provides valuable information on likely pathogenesis, particularly for unusual causes of stones such as cystinuria or crystallisation of drugs [17]. Patients with recurrent calcium or uric acid stones may benefit from oral citrate supplementation, which is effective even in the setting of normal urinary citrate levels. The high rates of recurrence, particularly in uric acid and cystine stone formers further highlights the importance of obtaining a baseline metabolic diagnosis for initial urinary stone presentations [18].

The detection of pure struvite stones also affects the patient's subsequent investigative pathway. Comprehensive metabolic assessment is not recommended in this group due to the low incidence of metabolic abnormalities detected, however, these patients should be managed with appropriate antibiotic therapy, urinary acidification, urinary tract infection prevention and regular radiological review [15, 19].

However, even if a stone is not available for analysis, such as in the case of spontaneous passage or following shock wave lithotripsy (SWL), alternative investigations can still be performed. In the case of a patient who has had a stent inserted, then encrustation analysis is usually consistent with that of the stone [20]. Alternatively, the patient should have 24-hour urine studies if deemed at high risk of stone recurrence.

General dietary counselling and lifestyle modification is recommended for all stone formers including adequate fluid intake of >2L per day, healthy weight range and reduced dietary salt [19]. More specific preventative strategies for stone disease are based on findings from stone analysis and 24-hour urine analyses [15] but are beyond the scope of this article. Spernat and Kourambas recently reviewed the literature regarding medical management and prevention of stone disease [21].

Our results demonstrate a consistency in stone analysis results over the past 30 years. As such, we would not recommend any change to current guidelines for metabolic assessment. There does not appear to be any emerging metabolic trend affecting the proportion of different stone types in Australia. As treatment and preventive strategies differ substantially between the 3 major stone types, we support the use of stone analysis in tailoring advice to patients who are concerned about their risk of stone recurrence.

Conclusion

From this study, stone composition in Australia has remained relatively static since the 1970s. Modifications in diet and body habitus have not resulted in significant changes in the proportion of uric acid and calcium oxalate stones detected. The decreasing trend in the proportion of struvite stones most likely reflects improved management of urinary tract infections within the Australian population.

Conflicts of Interest

None declared.

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