Date written: January 2025 – Public comment

Authors: CARI Guidelines Kidney Stones Working Group

GUIDELINE RECOMMENDATIONS
  1. We recommend low-dose non-contrast computed tomography scan for detection of suspected kidney stones in people with acute abdominal, flank or loin pain.
    (Strong recommendation, high certainty of the evidence)
  2. We suggest ultrasound may be used in the detection of recurrent uncomplicated (no infection, pain that subsides, non-obstructive) kidney stones for people presenting with acute abdominal, flank or loin pain, or for non-acute review of kidney stones.
    (Conditional recommendation, moderate certainty of the evidence)

Practice points

  • Computed tomography (CT) scan for the detection of suspected kidney stones is appropriate for people with first-time kidney stones but repeated scans for people with recurrent kidney stones is associated with increased harm from radiation.
  • Ultrasound is preferred for the following:
    • Pregnancy
    • Children
  • All people diagnosed with a kidney stone (even asymptomatic) should be informed of their diagnosis to support self-management, monitoring and nutrition therapy.
  • Urine should be strained for 48 hours following an acute pain episode from kidney stones for collection and analysis.
  • The majority of incidentally diagnosed kidney stones will remain asymptomatic.
  • Smaller (<4mm in diameter) kidney stones will increase the likelihood of spontaneous passage.
  • Risk factors for first-time stone formation:
    • Caucasian ethnicity
    • Family history of stones
    • Hot climates
    • Occupations associated with greater likelihood of experiencing dehydration (e.g., physical labour, teaching, truck driving), heat exposure (e.g., steel workers), and toxin exposure (e.g., manufacturing, ethylene glycol).
    • Medical conditions associated with kidney stones (hyperparathyroidism, sarcoidosis, gout, malabsorption (e.g., bariatric surgery), cystic fibrosis, immobilisation)
    • Metabolic abnormalities (hypercalciuria, hyperoxaluria, hyperuricosuria, hypocitraturia, type 2 diabetes, metabolic acidosis)
    • Kidney conditions (e.g., autosomal dominant polycystic kidney disease, medullary sponge kidney, distal renal tubular acidosis)
    • Medications and supplements associated with kidney stone formation (e.g., aspirin, certain antibiotics, certain antiretrovirals, certain anti-epileptics, prolonged high dose (≥1000 mg/day) vitamin C exposure, protease inhibitors, diuretics, and calcium supplements)
  • Risk factors for kidney stone recurrence:
Modifiable Non-modifiable
  • Higher BMI
  • High blood pressure
  • Low fluid intake
  • Low calcium intake
  • High sodium intake
  • High oxalate intake
  • High dietary acid load
  • Certain medications and supplements
  • Low urine pH
  • Brushite stones (calcium phosphate stone core)
  • Caucasian ethnicity
  • Family history of stones
  • Previous kidney stones
  • Hot climates (e.g., Southern Asia, Middle East)

Scope of the guidelines

These guidelines deal with the diagnosis of and risk factors for kidney stones in adults. Other clinical practice guidelines should guide diagnosis of and risk factors for kidney stones in children.

Background

Few studies have examined the incidence of kidney stones in Australia and Aotearoa New Zealand. Studies conducted in New Zealand indicate that the incidence of new kidney stones ranged from 85 per 100,000 to 131 per 100,000 people in Auckland (1, 2) between 2007 to 2015, and 105 per 100,000 people in Christchurch (3). Data from Australia is not as well described, with data from presentations with acute symptomatic urolithiasis reported as 6.7 per 1000 people from one tertiary Emergency Department in Melbourne (4). Seasonal variation in kidney stones is evident, with warmer climates experiencing increased incidence of kidney stones (5), which is also well described in our region (1).

The increasing incidence and high presentation rates at Emergency Departments highlight the need for appropriate identification of people with kidney stones. Additionally, participants at the CARI Guidelines kidney stones workshops in Aotearoa New Zealand expressed timely identification of kidney stones as a priority. Given the growing burden and emphasis on appropriate diagnosis by people with lived experience, up-to-date, evidence-based guidance for care is needed.

Implementation and audit

The use of ultrasound in the detection of kidney stones in people with recurrent kidney stones disease is an appropriate clinical quality indicator for people under 50 years of age. However, the working group acknowledges the access to ultrasound during out of hours is difficult due to limited resourcing in tertiary hospitals in Australia and New Zealand.

Guideline recommendations

We recommend low-dose non-contrast computed tomography scan for detection of suspected kidney stones in people with acute abdominal, flank or loin pain.
(Strong recommendation, high certainty of the evidence)

Rationale

Low-dose computed tomography (CT) has been found to have excellent accuracy (99% receiver operator curve) in the detection of kidney stones (6, 7), when compared to previous detection techniques such as intravenous urogram, but is associated with a high radiation exposure risk from repeated use (8). Patients have highlighted the importance of appropriate detection of kidney stones to support self-management and prevention of stone recurrence. Access to CT machines and staff with appropriate expertise is available to most emergency departments in Australia and Aotearoa New Zealand.

Benefits and harms

Systematic reviews of either standard or low-dose non-contrast CT have demonstrated its utility in the detection of uncomplicated symptomatic kidney stones. Low-dose CT scan has a sensitivity from 0.96 to 0.98 and specificity from 0.94 to 1.00 in the detection of kidney stones (6, 7, 9), and the summary receiver operator curve for low-dose CT for detection of kidney stones is 99% compared to intravenous urogram (6, 7). However, non-contrast CT is associated with high risk of radiation exposure; in a multi-centre randomised controlled trial comparing CT to radiology-performed ultrasound and point-of-care ultrasound to rule out kidney stones in people 18 to 76 years of age reporting flank or abdominal pain, participants reached a cumulative radiation exposure of 17.2 mSv (8).

Certainty of the evidence

The certainty of the evidence is high. The available systematic reviews (6, 7, 9) demonstrating the diagnostic accuracy of low-dose CT compared to ultrasound or intravenous urogram are well conducted, with no major concern of risk of bias for included studies.

Preferences and values

People with kidney stones at our CARI Guidelines kidney stones involvement workshops highlighted the frustration of delayed detection of kidney stones. Participants often described not receiving adequate diagnosis – “The first few times that I had it, I didn’t know what it was. And it never really got found out, because they pretty much sent me away” (Male, 50-59 years old) – highlighting the importance of appropriate imaging protocols for the detection of kidney stones.

Equity

The Working Group does not identify any other issue of equity that may be of concern.

Resources and other considerations

A cost-evaluation study of the multi-centre randomised controlled trial comparing CT with ultrasound in people with suspected kidney stones (8) was undertaken (10). While the cost of CT scan compared to ultrasound is slightly increased in initial Emergency Department visits ($423 compared to $448) (10), access to trained staff is not limited out of hours (i.e., weekends and nights) in Australia and Aotearoa New Zealand.

We suggest ultrasound may be used in the detection of recurrent uncomplicated (no infection, pain that subsides, non-obstructive) kidney stones for people presenting with acute abdominal, flank or loin pain, or for non-acute review of kidney stones.
(Conditional recommendation, moderate certainty of the evidence)

Rationale

Ultrasound compared to computed tomography (CT) has a lower specificity and sensitivity for the detection of kidney stones (11, 12). However, despite the better diagnostic performance of CT in detecting kidney stones, there is little to no benefit on patient-important outcomes and serious adverse events (8, 13), and an increased cumulative radiation exposure risk compared to ultrasound (8). In the presence of hydronephrosis, ultrasound in acute settings has improved sensitivity and may, overall, better explain clinical outcomes (12). As such, Choosing Wisely Australia (14) and Choosing Wisely United States of America (15) recommend avoidance of CT in people under the age of 50 years old with uncomplicated kidney stones. However, the clinical trial included participants up to 76 years of age (8), and the Working Group determined that the use of ultrasound should be considered for the detection of recurrent kidney stones in adults presenting with acute pain suspected from kidney stones, or non-acute review of kidney stones. Despite the increased costs and harms of CT compared to ultrasound, limited access to trained sonographers, particularly out of hours, i.e., overnight and weekends, and outside of metropolitan cities in Australia and New Zealand, may limit the use of ultrasound in the detection of kidney stones.

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Figure 1. Sensitivity and specificity forest plots in the detection of kidney stones comparing point-of-care ultrasound with reference standard CT scan demonstrating hydronephrosis from Wong et al., 2018.

Benefits and harms

The diagnostic performance of ultrasound compared to CT was assessed in the evidence review for these guidelines. A systematic review reported the pooled sensitivity of point-of-care ultrasound as 70.2% (95% CI: 67.1%, 73.2%) and specificity of 75.4% (95% CI: 72.5%, 78.2%), with the presence of hydronephrosis increasing the diagnostic performance (12). Another literature review found articles that examined radiology-performed ultrasound reported sensitivity from 57% to 91% (11). A multi-centre non-inferiority randomised controlled trial found that, based on the first ultrasound imaging test compared to CT had a lower sensitivity but higher specificity (point-of-care sensitivity 57% (95% CI: 51%, 64%) and specificity 71% (95% CI: 67%, 75%); radiology-performed sensitivity 88% (95% CI: 84%, 92%) and specificity 73% (95% CI: 69%, 77%)) (8).

Despite the improved diagnostic performance of CT in detecting kidney stones, studies have found that CT, compared to ultrasound, may have little to no effect on adverse events and patient-important outcomes (8, 13). In a single-centre retrospective study conducted in the USA, with the introduction of unenhanced helical CT, there has been little to no change in patient-important outcomes, including hospital admission, length of stay, return visit to the emergency department, or subsequent admission to the hospital (13). A multi-centre randomised controlled trial that compared CT, radiology-performed ultrasound, and point-of-care ultrasound to rule out kidney stones in people 18 to 76 years of age reporting flank or abdominal pain found no difference in serious adverse events, and no difference in return emergency department visits or hospitalisations. However, the use of ultrasound (point-of-care 9.3 mSv and radiology-performed 10.1 mSv) did decrease the 6-month cumulative radiation exposure compared to CT (17.2 mSv) (8).

Certainty of the evidence

The certainty of the evidence is moderate. The available systematic reviews (11, 12) demonstrating the diagnostic accuracy of ultrasound compared to CT found methodological limitations in the included studies. Only one randomised controlled trial (8) showed the increase in cumulative radiation from CT; hence, the certainty of this recommendation has been downgraded due to imprecision.

Preferences and values

Our CARI Guidelines consumer involvement workshops found that detecting kidney stones was important to understanding patients’ health and symptoms. However, there was no indication of a preference for imaging. This was also highlighted in a qualitative study conducted in Ireland with 33 people with recurrent kidney stones (16). Both studies indicated that diagnosis was imperative to self-managing kidney stone formation and recurrence.

Equity

Our pain management guidelines have recognised the disparity in managing acute pain from kidney stones (17). The Working Group recognises that our recommendation to de-emphasise CT scans in the detection of uncomplicated kidney stones in those with a previous history of stones may help improve clinical diagnosis and may result in more timely and appropriate pain management for patients. The Working Group does not identify any other issue of equity that may be of concern.

Resources and other considerations

The Melnikow et al. (2016) (10) cost-evaluation study of the multi-centre randomised controlled trial (8) estimated the cost of care for all enrolled participants of the study, applying United States of America (USA) Medicare reimbursement averages to initial emergency department visits, and evaluating initial hospitalisation and medical care over the following seven days. The study found a modest decrease in initial Emergency Department visit costs using ultrasound compared to CT ($423 compared to $449). A Monte Carlo simulation model indicated that, based on USA data on avoiding 159 000 (±18 000) CT scans annually, the implementation of the USA Choosing Wisely guidelines (15) resulted in a mean saving of $16.5 million (±$2.5 million), with avoidance of unnecessary radiation exposure. Point-of-care ultrasound in the detection of kidney stones will reduce barriers to access, with no requirement for specialist radiology staff or CT machines.

In Australia and Aotearoa New Zealand, despite the increased harms and costs of CT, ultrasound may be limited due to the lack of trained staff, i.e., sonographers.

Practice Points

Computed tomography (CT) scan for the detection of suspected kidney stones is appropriate for people with first-time kidney stones but repeated scans for people with recurrent kidney stones is associated with increased harm from radiation.

Rationale

CT has been found to have increased diagnostic performance in the detection of kidney stones (11, 12). A multi-centre randomised controlled trial found that CT had better sensitivity and specificity in ruling out kidney stones in adults (18 to 76 years of age) presenting in emergency departments with flank or abdominal pain (8).

Ultrasound is preferred for the following:

    • Pregnancy
    • Children

All people diagnosed with a kidney stone (even asymptomatic) should be informed of their diagnosis to support self-management, monitoring and nutrition therapy.

Urine should be strained for 48 hours following an acute pain episode from kidney stones for collection and analysis.

The majority of incidentally diagnosed kidney stones will remain asymptomatic.

Smaller (<4mm in diameter) kidney stones will increase the likelihood of spontaneous passage.

Rationale

Observational studies have reported that 38% to 71% of kidney stones <4 mm will be spontaneously passed, and only 4.8% of kidney stones <2 mm require intervention for removal (18). The location of the kidney stone has also been associated with spontaneous passage, with a higher likelihood for stones in the distal ureteral tract (45% – 71%) compared to the middle ureteral tract (22% – 46%) and proximal ureteral tract (12% – 22%). A systematic review of observational studies (18) reported a linear relationship between stone size and spontaneous passage, as detailed in Table 1.

Table 1. Association between size of kidney stone and spontaneous passage (18)

Size of kidney stone % spontaneously passed
1 mm 87%
4 mm 72%
7 mm 47%
10 mm 27%

Risk factors for first-time stone formation:

  • Caucasian ethnicity
  • Family history of stones
  • Hot climates
  • Occupations associated with greater likelihood of experiencing dehydration (e.g., physical labour, teaching, truck driving), heat exposure (e.g., steel workers), and toxin exposure (e.g., manufacturing, ethylene glycol).
  • Medical conditions associated with kidney stones (hyperparathyroidism, sarcoidosis, gout, malabsorption (e.g., bariatric surgery), cystic fibrosis, immobilisation)
  • Metabolic abnormalities (hypercalciuria, hyperoxaluria, hyperuricosuria, hypocitraturia, type 2 diabetes, metabolic acidosis)
  • Kidney conditions (e.g., autosomal dominant polycystic kidney disease, medullary sponge kidney, distal renal tubular acidosis)
  • Medications and supplements associated with kidney stone formation (e.g., aspirin, certain antibiotics, certain antiretrovirals, certain anti-epileptics, prolonged high dose (1000 mg/day) vitamin C exposure, protease inhibitors, diuretics, and calcium supplements)

Risk factors for kidney stone recurrence:

Modifiable Non-modifiable
  • Higher BMI
  • High blood pressure
  • Low fluid intake
  • Low calcium intake
  • High sodium intake
  • High oxalate intake
  • High dietary acid load
  • Certain medications and supplements
  • Low urine pH
  • Brushite stones (calcium phosphate stone core)
  • Caucasian ethnicity
  • Family history of stones
  • Previous kidney stones
  • Hot climates (e.g., Southern Asia, Middle East)
Rationale

The evidence review undertaken by CARI Guidelines identified five relevant systematic reviews (19-23). A systematic review (23), which included 53 observational studies, mainly from the United States of America and no studies from Australia and New Zealand, found the following likely unadjusted associations:

  • Higher BMI compared to lower BMI was associated with kidney stone recurrence (16 studies, n = 28 315, OR = 1.045, 95% CI: 1.008, 1.083).
  • High blood pressure, or the presence of hypertension compared to no hypertension was associated with increased stone recurrence (5 studies, n = 29 938, OR = 1.126, 95% CI: 1.076, 1.178)
  • Caucasian populations, compared to other ethnicities, had an increased rate of kidney stone recurrence (3 studies, n = 41 466, OR = 1.338, 95% CI: 1.003, 1.732).
  • Compared to non-uric acid stones, uric acid stones had a stronger association with kidney stone recurrence (4 studies, n = 4602, OR = 1.957, 95% CI: 1.414, 2.707). Brushite stones have also demonstrated elevated rates of kidney stone recurrence (24, 25).
  • Family history, compared to no family history had higher odds of kidney stone recurrence (12 studies, n = 11 912, OR = 1.194, 95% CI: 1.078, 1.323).
  • People with a history of kidney stones were more likely to have increased kidney stone recurrence (11 studies, n = 10 784, OR = 1.428, 95% CI: 1.230, 1.658) (23). In 25 randomised controlled trials, the median recurrence in people with a single kidney stone episode was 6 per 100 person-years compared to 16 per 100 person-years at trial enrolment (20).
  • In 12 of 13 identified studies across Asia, Europe, and New Zealand, higher monthly temperature has been associated with increased incidence of kidney stone recurrence over a mean of 5.5 years follow-up (21).
  • Brushite stones consist of a calcium phosphate core that is difficult to manage due to its high density and solidity.

 

Studies have demonstrated that nutrition status may be associated with kidney stone recurrence:

  • A higher calcium intake is associated with a decrease in kidney stone recurrence compared to a low calcium intake (26, 27). The Health Professionals Follow-up study found that, in 45 619 adults aged 40 to 75 years, the highest quintile of calcium intake compared to the lowest quintile reduced kidney stones risk (adjusted RR = 0.56, 95% CI: 0.43, 0.73) (26). Similarly, the United States National Health and Nutrition Examination Surveys confirmed the reverse association in lowest dietary calcium quintiles compared to highest quintiles (adjusted OR = 0.59, 95% CI: 0.41, 0.85) across models in 15 364 adults in 1976 to 1980 and 16 115 adults in 1988 to 1994 (27).
  • Animal protein is negatively associated with renal acid load, reducing urine pH, while fruits and vegetables contribute a strong alkali load, increasing urine pH (28). Observational studies have demonstrated that, in people who experience calcium stone formation, dietary renal acid load is higher (12.7 mEq/day) compared to healthy controls from the same single centre in Italy (29). A case-control study found that the highest tertile of net endogenous acid production was associated with an increased risk (OR = 1.88, 95% CI: 1.14, 3.09) of calcium oxalate stones (30).

The CARI Guidelines consumer involvement workshops conducted in Aotearoa New Zealand in May 2021 found that participants who were not considered ‘typical’ stone formers, e.g., women, non-white, were often overlooked and undiagnosed with new or recurrent kidney stones.

Suggestions for future research

  • Further examination of monogenetic forms of kidney stone disease are required to inform genetic testing and clinical management of disease.

Systematic reviews of observational studies and genome-wide association studies have identified various gene polymorphisms that may be associated with kidney stone formation and recurrence (19, 22).

  • Data analysis of acute urolithiasis presentation, stone characteristics, and identified risk factors is required to improve approaches to diagnosis, management, and prevention.

Kidney Stones Working Group

David J. Tunnicliffe1,2

Andrew J Mallett3,4,5,

Hicham Hassan 6,7*

Adam Mullan8

Lyn Lloyd9

Ieuan Wickham10

Brydee Cashmore1,2

Adela Yip1,2

Alex Currie10

Matthew Jose12, 13*

*Authors have contributed equally as Co-Convenors of the Guideline Working Group.

Affiliations

  1. Sydney School of Public Health, The University of Sydney, Sydney, NSW, Australia
  2. Centre for Kidney Research, The Children’s Hospital at Westmead, Sydney, NSW,
  3. Department of Renal Medicine, Townsville University Hospital, Douglas, Queensland, Australia
  4. College of Medicine and Dentistry, James Cook University, Douglas, Queensland, Australia
  5. Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
  6. Graduate School of Medicine, University of Wollongong, Wollongong, NSW, Australia
  7. School of Medicine, Lebanese American University School of Medicine, Beirut, Lebanon
  8. Northland Renal Services, Te Tai Tokerau, Northland, New Zealand
  9. Nutrition and Dietetics, Te Toka Tumai, Auckland, Health New Zealand
  10. Consumer partner
  11. University of Tasmania, Hobart
  12. Department of Renal Medicine Royal Hobart Hospital, Hobart

Conflict of interest

The CARI Kidney Stones Working Group have no relevant conflicts of interests to report.

Funding

CARI Guidelines receives funding from the Australian and New Zealand Society of Nephrology, the Australian Living Evidence Collaboration, and the National Health and Medical Research Council Emerging Leadership 1 Investigator grant (APP1197337).

References

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