Nephrolithiasis encompasses the formation of all types of urinary calculi in the kidney, which may be deposited along the entire urogenital tract, from the renal pelvis to the urethra. Risk factors include low fluid intake and high-sodium, high-purine, low-potassium diets, which can raise the calcium, uric acid, and oxalate levels in the urine and thereby promote stone formation. Urinary stones are most commonly composed of calcium oxalate. Less common stones are composed of uric acid, struvite (due to infection with urease-producing bacteria), calcium phosphate, or cystine. Nephrolithiasis manifests as sudden-onset colicky flank pain that may radiate to the groin, testes, or labia, commonly called renal or ureteric colic, and it is usually associated with hematuria. Diagnostics include spiral CT without contrast and/or ultrasound of the abdomen and pelvis to detect the stone, as well as urinalysis to assess for concomitant urinary tract infection (UTI) and serum BUN and creatinine to evaluate kidney function. Small stones that do not require urgent urological intervention can be managed with symptomatic treatment and a trial of medical expulsive therapy to promote spontaneous passage. If spontaneous passage appears unlikely or fails because of the size or location of the stone, first-line urological interventions include shock wave lithotripsy, ureterorenoscopy, and, in patients with large kidney stones, percutaneous nephrolithotomy. The most important preventive measure is adequate hydration. In addition, the analysis of passed stones may provide information to guide dietary changes and/or medical therapy (e.g., thiazide diuretics, urine alkalinization) that can prevent future stone formation.
Overview of kidney stones
|Types||Incidence||Etiology/associated findings||Urine pH|
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|Uric acid stones|| || || |
|Struvite stones|| || || || |
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|Cystine stones|| || || || |
|Xanthine stones|| || || || |
Calcium oxalate stones 
- Calcium oxalate monohydrate (whewellite): brown or black calculi
- Calcium oxalate dihydrate (weddellite): light yellow calculi
- Hypercalciuria: presence of elevated calcium levels in the urine
Hyperoxaluria: presence of elevated oxalate levels in the urine
- Increased intake of dietary oxalate
Increased intestinal absorption of oxalate, e.g., due to fatty acid malabsorption (e.g., Crohn disease, ulcerative colitis, short bowel syndrome)
- Calcium normally binds oxalate to form calcium oxalate, which is excreted via feces.
- In conditions associated with fatty acid malabsorption due to impaired bile acid reabsorption, calcium preferentially binds free fatty acids, leading to excess free oxalate and, therefore, to increased oxalate absorption.
- Vitamin C supplements
- Pyridoxine deficiency 
- Hypocitraturia: decreased level of citrate in the urine
- Hyperuricosuria: increased urinary excretion of uric acid
- Develop in persistently acidic urine
- Dietary modification
- Thiazide diuretics for recurrent calcium-containing stones with idiopathic hypercalciuria (i.e., no hypercalcemia)
- (e.g., with potassium citrate)
- Possibly citrate supplementation
Uric acid stones
Uric acid stones are radiolUcent (x-ray negative).
Struvite stones (magnesium ammonium phosphate stones)
- Upper UTI with such as Proteus mirabilis, Klebsiella, Staphylococcus saprophyticus, and/or Pseudomonas
- Use of indwelling catheter increases risk
- Develop in persistently alkalic urine
Calcium phosphate stones 
- Carbonate apatite
Cystine stones 
- Clinical features: recurrent kidney stones (manifesting with e.g., flank pain) starting in childhood
- Etiology: xanthinuria
- Treatment: reduced dietary intake of purines
- Etiology: increased urinary 2,8-dihydroxyadenine concentration due to hereditary deficiency of adenine phosphoribosyltransferase
- Treatment: allopurinol OR febuxostat
Ammonium urate stones
- Etiology: urinary tract infection, malabsorption, hypokalemia
Can be caused by:
- Crystallization of drug compounds in the urine, which is most commonly associated with:
- Stone formation due to alterations in urine composition, which are most commonly associated with:
Stones usually form in the collecting ducts of the kidneys but may be deposited along the entire urogenital tract from the renal pelvis to the urethra. Their localization and size determine the specific symptoms. Small kidney stones may also be asymptomatic and detected incidentally. 
- Severe unilateral and colicky flank pain (renal colic) ; 
- Nausea, vomiting, and reduced bowel sounds
- Dysuria, frequency, and urgency
- Passage of gravel or a stone
- Patients are usually unable to sit still and move around frequently (opposed to patients with peritonitis, who usually prefer to lie still)
- Clinical suspicion: Consider nephrolithiasis in patients with unilateral colicky flank pain associated with nausea, vomiting, and/or hematuria.
- Initial diagnostics
- Further evaluation
Laboratory studies 
- CBC: ↑ WBC count 
- Nonspecific findings of nephrolithiasis
- Gross or microscopic hematuria
- Nonspecific leukocyturia, bacteriuria , e.g., positive or nitrites,
- Findings suggestive of stone composition
Imaging studies 
- Recommendations in this section are consistent with the 2015 American College of Radiology (ACR) appropriateness criteria for acute-onset flank pain with suspicion of stone disease. 
- In general, an initial presentation suspicious for nephrolithiasis requires confirmatory CT imaging.
- Imaging is also indicated for acute flank pain of uncertain etiology, e.g., to rule out AAA.
- Routine CT is controversial in young patients with uncomplicated presentations of renal colic , especially those with a history of nephrolithiasis. 
CT abdomen and pelvis without IV contrast
- Type: low-dose, helical (spiral) CT without contrast
- Indication: first-line for nonpregnant patients with suspected nephrolithiasis
- Findings 
The addition of IV contrast may help to differentiate ureteral stones from phleboliths and increases the likelihood of detecting alternative causes of abdominal pain (e.g., appendicitis, diverticulitis). However, IV contrast reduces the sensitivity for kidney stones to ∼ 80% compared to > 95% in CT without contrast. 
Ultrasound abdomen and pelvis
- Indications: suspected nephrolithiasis in patients for whom radiation exposure should be minimized (e.g., pregnant patients, pediatric patients, those with recurrent stones)
- Indications: follow-up for previously identified radiopaque stones after the initiation of treatment
- Findings: radiographic densities (e.g., stones, phleboliths, vascular calcifications)
Because KUB sensitivity is proportional to stone size, it is usually only suitable for larger stones.
- Indications: suspected nephrolithiasis in patients for whom radiation exposure should be minimized (e.g., pregnant patients or children)
- Findings: similar to CT
Intravenous pyelogram (IVP)
- Indications: rarely indicated given the broad availability of CT
- Provides a complete outline of the urinary tract system
- Size and location of stone, degree of obstruction
Further evaluation 
For initial episodes of nephrolithiasis, patients should undergo a limited metabolic evaluation to rule out underlying systemic disorders and guide preventative therapy. This workup is typically unnecessary following repeat visits for renal colic where the underlying etiology is already known.
- Dietary history: fluid intake, protein, calcium, sodium, fruits, vegetables, high-oxalate foods, over-the-counter supplements
- Laboratory studies: BMP , calcium , uric acid , urinalysis
- Stone composition analysis 
- 24-hour urine profile
Provide patients with a first-time diagnosis of nephrolithiasis with a urine strainer at the time of discharge to collect passed stones for compositional analysis during their follow-up.
Recommendations in this section are consistent with the 2016 American Urological Association (AUA) guideline on the surgical management of kidney stones and the 2019 AUA guideline on the medical management of kidney stones. 
- Initiate symptomatic management prior to confirmatory imaging for patients with renal colic.
- Consult urology urgently for interventional treatment in the following cases:
- Attempt a trial of conservative management for patients with small (≤ 10 mm), uncomplicated stones.
- Disposition: Most patients with uncomplicated nephrolithiasis can be treated successfully with
during an emergency department visit of a few hours.
- Admit patients requiring urgent urology consult and intervention.
- Ensure outpatient urology follow-up for all patients eligible for discharge (e.g., no indications for urgent urology consult, resolved symptoms, no complications).
- Tailor recurrence prevention measures to the type of stone; see “Prevention” for details.
The larger the stone, the less likely it is to pass spontaneously.
Obstructing nephrolithiasis with suspected infection requires urgent urology consultation and management. 
Symptomatic management 
- Antiemetics, e.g., ondansetron (off-label)
- Intravenous fluids for dehydration
Conservative management 
- Initiate medical expulsive therapy (MET).
- Provide antibiotic treatment if urinalysis indicates a UTI; for specific recommendations, see:
- “ ”
- “ ”
Interventional management 
The choice of interventional treatment is based on the size and location of the stone, suspected infection, and shared decision-making.
- Infected stones: or to relieve obstruction; delayed definitive management
- Ureteral stones
- Renal stones ≤ 20 mm OR lower renal pole stones ≤ 10 mm: URS or ESWL
- Renal stones > 20 mm OR lower renal pole stones > 10 mm: percutaneous nephrolithotomy (PCNL)
|Urological interventions for nephrolithiasis |
|Extracorporeal shock wave lithotripsy (ESWL)|| |
|Percutaneous nephrolithotomy (PCNL)|| |
The need for follow-up imaging after conservative or interventional management depends on the symptoms, stone type, and intervention modality.
Acute management checklist
- Keep patient NPO.
- Provide symptomatic management (e.g., analgesia, antiemetics).
- Obtain CT abdomen and pelvis without IV contrast if indicated (e.g., first presentation of renal colic, flank pain with uncertain diagnosis).
- Evaluate for indications for urgent interventional management of nephrolithiasis.
- Consider conservative management with medical expulsive therapy.
- Refer to urology for follow-up and further workup of etiology of nephrolithiasis.
- Hydration: sufficient fluid intake (≥ 2.5 L/day) 
- For calcium stones:
- For uric acid stones: low in purine
- For cystine stones: low in sodium
Change urinary pH: depends on stone composition
- Urine alkalinization: a treatment regimen to raise urinary pH to 6.5–7.5
- Urine acidification: a treatment regimen to lower the urinary pH to ≤ 7
Low calcium diets increase the risk of calcium-containing stone formation because they increase oxalate reabsorption.
Special patient groups
Nephrolithiasis in pregnancy
- Epidemiology: ∼ 1:3000 pregnancies 
- Risk factors
- Clinical features: See above.
- Diagnostics: Renal ultrasonography is preferred.