2nd February 2018, Volume 131 Number 1469

Stephanie Loeff, Manmeet Saluja, Michael Rice

Acute urolithiasis can be an extremely disabling condition and represents a substantial proportion of everyday urology practice. The incidence of urolithiasis has increased both within New Zealand and globally over the last few decades.1–3 In the US, incidence rates are as high as 10.6% in men and 7.1% in women.3 This rising trend could partially be attributed to changing lifestyle factors, as diseases such as obesity, diabetes and metabolic syndrome are on the rise and are related with stone formation.4–6 Naturally, morbidity and healthcare costs attributable to acute kidney stone disease is further increasing. Henceforward, the focus on prevention is becoming more important.

Auckland has an estimated population of approximately 1.5 million people7 with a variable ethnicity. The majority of the population is Caucasian (59%), followed by Asian (23%), Polynesian (15%), Māori (11%) and a smaller Middle Eastern (2%) population. Patient demographics were studied to evaluate which patient groups are most likely affected. Stone characteristics, current management and prevention strategies were analysed with the prospect of improving future practice.

This review is related to an existing line of research performed in the Auckland City Hospital, which adopted the same inclusion criteria. Subsequently, the incidence rate was compared with previous numbers, in order to monitor a potential rise in incidence. We hypothesised that the overall incidence of acute urolithiasis had increased compared to 2006.3


All patients that presented acutely to the Auckland District Health Board (ADHB) between July 2014 and June 2015 with symptomatic and radiologically diagnosed urolithiasis were retrospectively reviewed. Patients could have their first encounter or a recurrent presentation within the study period with a new stone. Clinical data was obtained from medical records after the study was ethically approved. Stones were mostly diagnosed with a non-contrast CTKidney, ureter, bladder (KUB) as per hospital protocol, however an ultrasound KUB was preferentially used in younger women. Population data was based on estimates provided by the Ministry of Health and Statistics as the national census was last updated in June 2013.

Statistical Analysis Software programme (SAS) was used for analysis and comparisons were made by means of two-tailed tests and Pearson Chi-Square test. ROKS (recurrence of kidney stone) nomogram was used to predict the risk of a second kidney stone epidose recurrent. The scores are based on the predictive power developed following a large historic cohort study, whereby potential risk factors for recurrence in first-time stone formers were identified.8 The rates were subsequently calculated by using the QMXD calculator, which has been implemented for the nomogram (http://qxmd.com/calculate/roks-recurrence-of-kidney-stone-2014).


Incidence and demographics

A total of 1,328 new presentations of acute urolithiasis were identified among 1,125 patients. Nine hundred and seventy-two (86%) patients had a singular presentation. The remaining 153 (14%) patients had recurrent presentation(s) within the study period (Figure 1).

Figure 1: Number of patients presenting with acute renal colic events within the study period.



The incidence rate calculated by means of the estimated population data was 85 per 100,000 (0.085%). Although the number of events has increased compared to 2006, the overall incidence has decreased from 0.132%.1

Mean age of presentation was 48.9 years for men and 46.1 years for women. Since 2006, the 60–69 age group showed a significant increase in incidence, while the other age groups showed a decrease (Figure 2). Males (68%) were more likely to be affected than females (32%), and remained similar to the proportions in 2006.

Figure 2: Age distribution of patients in 2006 and 2014. 


From the ethnic subgroups, caucasians predominated and constituted 57% of the study population for both 2006 and 2014. The Asian population showed a significant increase in incidence, whereas the Pacific Island group has had a significant decrease in incidence (Table 1). The Middle Eastern population continued to have the highest overall incidence of acute urolithiasis.

Table 1: Incidence and distribution of nephrolithiasis by ethnicity in 2006 and 2014.


Distribution of nephrolithiasis by ethnicity




Middle Eastern



304 (24%)

741 (57%)

119 (9%)

29 (2%)

94 (7%)


204 (16%)

719 (57%)

109 (9%)

27 (2%)

142 (11%)








Incidence of nephrolithiasis by ethnicity




Middle Eastern














A substantial large group of 720 cases (56%) were either recurrent or ‘high risk’ stone formers as defined by the EAU guidelines.9 As many as 46% reported having a previous episode of renal colic(s) in their lifetime. For the majority of this group (77%), a singular previous episode was reported. (Table 2). Metabolic syndrome was recorded as the most common morbidity associated with ‘high risk’ patients (Table 3). From the ROKS nomogram, it was estimated that recurrence risk in the first-time symptomatic stone former was 7% at two years, 14% at five years and 23% at 10 years.

Table 2: Recurrent stone formers.

Previous episodes



693 (54%)


455 (35%)


84 (7%)


28 (2%)


26 (2%) 

Table 3: Factors associated with increased risk.

High-risk stone formers


Early onset


Familial stone formation


Struvite/uric acid containing stones*


Metabolic syndrome (BMI >30)










Cystics fibrosis




Horseshoe kidney


Solitary kidney


Xanthogranulomatous pyelonephritis


Medullary sponge kidney


Renal tubular acidosis


Sjorgen syndrome


Spina bifida


* Stones which constituted some struvite or uric acid of the total composition were also included. 

Stone characteristics

Seventy-four percent of stones smaller than 5mm were found in the distal ureter or recently passed into the bladder. As expected, distal stones were smaller and proximal stones tended to be larger (Table 4).Of the cases presented, 47% had multiple stones, this mostly involved small non-obstructing, intra-renal stones.

Table 4: Stone position by size and location.

 Location symptomatic stone

Size stone in mm






299 (74%)

48 (12%)

56 (14%)



240 (43%)

104 (19%)

208 (38%)



23 (19%)

15 (12%)

83 (69%)



15 (28%)

3 (5%)

36 (67%)


Management of urolithiasis

Seven hundred and thirty-nine cases (57%) were managed conservatively without further treatment or intervention being required. An additional 70 cases failed conservative management and needed elective surgery. Smaller and more distal stones were more likely to be managed conservatively (Table 5). A total of 622 surgeries were performed with ureteroscopy accounting for the majority (81%). ESWL (9%) and PCNL (3%) were less commonly performed. Three (0.5%) nephrectomies were performed due to xanthogranulomatous pyelonephritis.

Table 5: Management by stone size.

Size in mm





Conservative management

334 (83%)

245 (44%)

18 (15%)

15 (27%)

Intervention; surgical/ ESWL

69 (17%)

307 (56%)

103 (85%)

40 (73%)






 (Chi-square = 293,323a p<0.001, 8 df). 

Metabolic work up

Table 6 shows the performed metabolic work-up. The investigations recommended by the EAU were hereby set as a standard. Basic serum and urine analysis were performed in most patients; however, serum calcium and phosphate levels were measured in only half the cases. Two hundred and three (15%) cases had a urinary tract infection diagnosed on microscopy. Gram negative organisms constituted the most common growth.

Thirty-six percent of patients who had surgery had stone analysis compared to 7% with conservative management. Calculi analysis yielded 42% of calcium oxalate, 33% of calcium oxalate-phospate and 11% of predominant uric acid components (Figure 3).

Figure 3: Stone composition. 


Overall, 24-hour urine analysis and dietician review was performed poorly for high-risk and recurrent stone formers during the study period, however some of the recurrent stone formers may have had metabolic workup performed previously (Table 6).

Table 6: Overview of completed metabolic work-up.






827 (64%)

382 (29%)

86 (7%)


530 (64%)


25 (29%)


296 (36%)

382 (100%)

61 (71%)

Stone analysis

228 (28%)

22 (6%)

8 (9%)


192 (84%)


5 (63%)*


36 (16%)

22 (100%)**

3 (38%)

Basic analysis—blood


816 (99%)

379 (99%)

84 (98%)


816 (99%)

379 (99%)

84 (98%)


816 (99%)

379 (99%)

84 (98%)


498 (60%)

211 (55%)

45 (52%)

Uric Acid

446 (54%)

202 (53%)

29 (34%)

Basic analysis—urine


806 (97%)

377 (99%)

84 (98%)


806 (97%)

377 (99%)

84 (98%)


806 (97%)

377 (99%)

84 (98%)


806 (97%)

377 (99%)

84 (98%)


806 (97%)

377 (99%)

84 (98%)


718 (87%)

349 (91%)

80 (93%)

High risk and recurrence

499 (60%)

177 (46%)

44 (51%)

24 hr urine

77 (15%)

14 (8%)**

16 (36%)**

 Seen by dietician

 22 (4%)

 5 (3%)**

 5 (11%)

*These surgeries were performed by the urology department but were discharged from different wards due to coexistent health issues.
**Stone analysis and 24 hr urine performed by the urology/renal department after referral. 


According to this study, acute kidney stone disease has decreased in incidence for the Auckland region compared 0,132% in 2006 to 0,085. It must be stated that in this period, Auckland has had an 11% population growth from 1,373,000 (2006) to 1,526,900 (2014).

During the same period of time, there has been a major influx in the Asian population with an increase of 30% in their population (268,700 in 2006 to 348,900 in 2013).7 The lower incidence of urolithiasis in the Asian population could therefore account for the overall decrease in the incidence of urolithiasis. This is an important finding of this study as it suggests that mass migration influences the incidence of acute nephrolithiasis. There is no other literature that discusses this phenomenon and further hypothesis generating could be considered.

Almost two-thirds of patients were identified as high-risk or recurrent stone formers. Even within a year, more than 10% of patients had a recurrent presentation with another stone. This demonstrates the large burden of stone disease in our population and emphasises the need of prevention. Both basic and 24-hour metabolic analysis was inadequately performed. Both are fundamental prior to medical/dietary follow-up and are considered standard of care.9

These trends are also seen elsewhere in the world; a large series showed a prevalence of metabolic workup in high-risk patients in only 7.4%.12 Dietician referrals were also infrequent even though these patients may benefit from a personalised dietary plan.10 Henceforward, our department has set a more targeted focus on prevention management by means of a dedicated renal team. To achieve this goal, an adequate metabolic evaluation beforehand is now being routinely performed for high-risk patients. Patient education, medical management and dietician input are now being offered and implemented in our stone clinic.

Although more than half of the cases were managed conservatively, primary ureteroscopy was used in the majority of surgical treatments. Auckland is unique, as the acute services can accommodate an after-hours laser service with availability of theatre and medical expertise. However, there is enormous stress on elective services if primary ureteroscopy is not possible. As such, alternative surgical options such as ESWL, which has similar efficacy in proximal stones, could be better utilised in the future.13

There are a few limitations to the study. All symptomatic stones referred to the ADHB were incorporated. This study is based on public hospital-statistics, therefore presentations at general practices or private hospitals were not included. The true incidence of acute urolithiasis in Auckland is likely to be higher than quoted in our study. Furthermore, there may have been changes in patient flows regarding public versus private health. However, since there is very limited data available on this matter, no conclusions can be drawn. Patients’ BMI and family history were grossly under-reported in patient records and no major conclusions could be drawn regarding these two variables.

Aetiological factors which may contribute to the formation of nephrolithiasis, such as geographical location, water hardness,11 have not been taken into account as these variables were the same for both datasets. Previous research conducted in Auckland has shown that there are clear seasonal variations on the incidence of stone disease, as with higher temperatures and increased sun hours correspond with a higher incidence. These components are not accounted as confounding factors in this present study.

A strength of this study is that there were no exclusion criteria; all people presenting to the ADHB with renal colic were included. Moreover, almost without exception all the cases had received imaging. Furthermore, the same inclusion criteria applied for the previous Auckland urolithiasis research conducted, which was also performed in the public-hospital setting. Therefore, the comparisons made between the two study populations and the conclusions drawn ought to be legitimate for the ADHB hospitals and gives a clear insight on the epidemiological trend of this disease.


Although the number of cases presenting with acute urolithiasis in Auckland has increased, there is an overall decrease in incidence. This deviation is attributed to the large influx of Asian immigrants observed in this period. A Caucasian male between 40–49 years with a calculus <5mm in the lower urinary tract has the highest chance of presenting with a renal colic. Metabolic workup and dietary management of these patients needs to be improved. Further prospective studies are needed once prevention strategies are implemented to monitor a reduction of recurrent symptomatic urolithiasis events in our population.


Decreasing incidence of symptomatic stones which could be attributed to a large influx of Asian immigrants. A male aged 40–49 with a past history of stones has the highest chance of stone formation.



To evaluate the incidence of acute symptomatic urolithiasis in the Auckland region. Associated epidemiological factors and stone characteristics were also studied and compared to previous research conducted in order to analyse trends.


All patients that presented acutely with symptomatic urolithiasis to the Auckland District Health Board (AHDB) between July 2014 and June 2015 were studied. Clinical data was obtained from medical records and population data was based on estimates provided by the Ministry of Health. Two-tailed tests and the Pearson Chi-Square tests were used for analysis.


Overall, 1,125 patients (1,328 events) presented with an incidence of 85 per 100,000 per year, which was lower than that reported in 2006. The highest incidence was found among the Middle Eastern ethnic subgroup (0.130 %), followed by Māori (0.102%), Asian (0.087%), European (0.084%) and Pacific (0.041%) ethnicity. Males were more likely to be affected than females. Urolithiasis was most common in the fifth decade of life (25%). Forty-seven percent of the study population presented with multiple stones and 64% had recurrent urolithiasis or were ‘high risk’ stone formers. Distal ureteric stones <5mm were the most common (27%). Urine cultures were positive in 16% of cases. Seven hundred and thirty-nine (57%) were managed with medical management and ureteroscopy was most commonly performed for those who needed surgical intervention.


The overall incidence of urolithiasis has decreased compared to previous research conducted in Auckland. This deviation could be attributed to the large influx of Asian immigrants observed in this period of time. A caucasian male, between 40–49 years, with a calculus <5mm in the distal ureter with a history of a previous urolithiasis has the highest chance to present with renal colic.

Author Information

Stephanie Loeff, Auckland Hospital, Auckland; Universitair Medisch Centrum Groningen, the Netherlands; Manmeet Saluja, Auckland Hospital, Auckland;
Michael Rice, Auckland Hospital, Auckland.


Dr Roger Chambers, B Rong Hu.


Michael Rice, Urology, Auckland Hospital, Auckland.

Correspondence Email


Competing Interests



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