Recommendations
Key Recommendations
The cardinal symptom is severe, acute flank pain, which may radiate to the ipsilateral groin and is commonly associated with nausea and vomiting. Bear in mind that some patients are asymptomatic.
Request laboratory tests for all patients to include:
Urinalysis
FBC
Serum chemistry (calcium, electrolytes, serum urea/creatinine, phosphorus, and uric acid).
Request a urine pregnancy test if the patient is a woman of childbearing age.
Arrange urgent (within 24 hours of presentation) low-dose non-contrast computed tomography (NCCT) for adults with suspected renal colic.[16]
If the patient is pregnant or aged under 16 years, arrange an urgent ultrasound instead of CT.[16]
Consider referring children and young people aged under 16 years to a paediatric nephrologist or paediatric urologist for assessment and metabolic investigations.[16]
Suspect nephrolithiasis based on the clinical history, physical examination findings, and laboratory test results; confirm the diagnosis with imaging studies.
Consider referring children and young people (under 16 years) to a paediatric nephrologist or paediatric urologist with expertise in this area for assessment and metabolic investigations.[16]
Renal and ureteric stones can cause renal colic: severe, acute flank pain that may radiate to the ipsilateral groin, commonly associated with nausea and vomiting. Rarely, this is accompanied by macroscopic haematuria.
As stones pass and get lodged in the distal ureter or intramural tunnel, this can lead to bladder irritation manifested as urinary frequency or urgency.
Ipsilateral testicular and groin pain may occur rarely in men with passing stones. However, calculi may also be asymptomatic.
In patients with renal colic, costovertebral angle and ipsilateral flank tenderness may be pronounced. Signs of sepsis, including fever, tachycardia, and hypotension, might indicate an obstructing stone with infection, warranting urgent urology referral.
For all patients with suspected nephrolithiasis, request:
Urinalysis[48]
FBC
Serum chemistry; including:[47]
Calcium[16]
Electrolytes
Serum urea/creatinine (to assess renal function)
Phosphorus
Uric acid.
A urine pregnancy test in women of childbearing age
To rule out ectopic pregnancy as the cause of symptoms
Prior to imaging with ionising radiation; see Urgent imaging section below.
Urinalysis is helpful in confirming a diagnosis of renal stones as microscopic haematuria is present in the majority of patients.[49] However, the absence of haematuria does not exclude nephrolithiasis.[50] Presence of >5 to 10 WBCs per high-powered field in urine or pyuria could indicate presence of urinary tract infection or be secondary to inflammation. Urinary crystals of calcium oxalate, uric acid, or cystine may indicate the nature of the calculus, although only cystine crystals are pathognomonic for the underlying type of stones. A urine pH >7 suggests presence of urea-splitting organisms, such as Proteus, Pseudomonas, or Klebsiella species, and struvite stones. A urine pH <5.5 suggests uric acid stones.
Request a urine screen for cystine if the diagnosis of cystinuria is not excluded by stone analysis: in particular, if the patient is a child or young adult presenting with large or recurrent stones.[3]
Consider stone analysis for all adults with ureteric or renal stones.[16] Do this after they are extracted during surgery or when patients expel and collect them for analysis.[47]
Analysis of stone composition provides information on chemical composition and aetiology and can guide preventative management.
A raised WBC count may indicate infection (pyelonephritis or urinary tract infection). Hypercalcaemia may suggest hyperparathyroidism as an underlying aetiology; measure serum parathyroid hormone in patients with high or high-normal serum calcium results.[51] Hyperuricaemia may indicate gout. Bear in mind that patients with gout don't necessarily get uric acid stones (they may get other types) and patients with uric acid stones don't necessarily get gout.
Non-pregnant patients
Request an urgent (within 24 hours of presentation) low-dose non-contrast computed tomography (NCCT) scan for any non-pregnant adult patient with suspected renal colic.[16]
Request an urgent (within 24 hours of presentation) ultrasound for any child or young person (under 16 years) with suspected renal colic.[16]
NCCT is the preferred imaging modality in non-pregnant adults due to its high sensitivity and specificity. NCCT accurately determines presence, size, and location of stones; if it is negative, nephrolithiasis can be ruled out with high likelihood. A low-dose non-contrast CT (<4 mSv) is preferred for patients with a body mass index (BMI) ≤30 kg/m², as this limits the potential radiation exposure while maintaining both sensitivity and specificity at 90% or higher.[52] Low-dose CT is not recommended for those with a BMI >30 kg/m², owing to lower sensitivity and specificity in these patients. CT scans are also used when patients with known stones have new onset of renal colic because stones commonly change location or new ones are formed. Bear in mind that there is a risk of significant radiation exposure with repeated CT scans, and you should use your clinical judgement.
If the patient's stone is not visible on the NCCT scout film, use plain abdominal kidney-ureter-bladder radiography (KUB) to determine whether stones are radiopaque and to monitor the stone episode.[52] If the patient’s stone is visible on the NCCT scout film, consider follow up with KUB. In practice in the UK, NCCT and KUB are often both carried out at initial presentation.
Calcium oxalate and calcium phosphate stones are radiopaque, whereas pure uric acid and indinavir stones are radiolucent and cystine stones are partially radiolucent.
Renal ultrasound can be used to diagnose renal stones, particularly in pregnancy (see Pregnant women below), in children, or other situations where avoiding radiation exposure is advised, although it can be operator dependent and has low sensitivity for diagnosing mid and distal ureteric stones.[53] The combination of renal ultrasonography with KUB has been proposed as a reasonable initial evaluation protocol when a CT scan cannot be performed or is unavailable. For a known stone former who has previously had radiopaque stones, it has been suggested that a combination of renal ultrasonography and KUB is a viable option for follow-up imaging; sensitivities and specificities each up to 100% have been reported for this combination of modalities.[54][55][56]
Renal ultrasound and CT have been investigated to compare their safety and efficacy as an initial diagnostic test for patients who present to the emergency department with suspected nephrolithiasis. The results of a large, multicentre study showed no significant difference in high-risk diagnoses, serious adverse events, subsequent emergency department visits, or hospitalisations in those undergoing CT or renal ultrasound in this setting.[57] Another multicentre randomised trial found that of 1666 patients diagnosed with nephrolithiasis in the emergency department (following abdominal ultrasound or CT), the majority of patients (78%) ultimately had CT performed before elective intervention. Patients whose ultrasound was performed by an emergency department physician were 2.6 times more likely to undergo CT before intervention than those whose ultrasound was performed by a radiologist. Ultrasound as the initial imaging modality did not result in a significant delay to intervention.[58]
Point-of-care ultrasound (POCUS) may have a role in screening symptomatic patients. A systematic review and meta-analysis assessing POCUS performed in the emergency department studied 1773 patients, and showed sensitivity of 70% and specificity of 75% for diagnosing nephrolithiasis.[59] Moderate to severe hydronephrosis was shown to be highly specific for the presence of stones, and any hydronephrosis is suggestive of a large stone (>5 mm) in those presenting with renal colic.[59] POCUS was not shown to be associated with any increased risk to the patient.[59] POCUS may therefore have a role in sparing patients with a negative POCUS from further imaging, although those with a positive test will likely need definitive imaging to guide further management.
Dual-energy CT is an emerging test that is able to detect uric acid stones without needing stone analysis.[60] It may be able to replace stone analysis as the diagnostic test for these types of stones, and therefore potentially facilitate earlier initiation of treatment with urinary alkalinisation.[60]
Pregnant women
If the patient is pregnant, request an urgent (within 24 hours of presentation) renal ultrasound instead of CT.[16][47]
For pregnant patients when renal ultrasound is non-diagnostic, transvaginal ultrasound can assist with diagnosis by determining if ureteral dilation extends beyond the pelvic brim; it can also diagnose stones in the distal ureter.
Magnetic resonance imaging (MRI), which confers no radiation to the patient, is a second-line imaging modality because stones are not directly visible on MRI and only seen as a filling defect in the collecting system.[47]
Radiation doses of <50 mGy have not been associated with increased risk of fetal anomalies or loss; therefore, low-dose protocol CT (<4 mGy) can be considered as a last-line option in pregnant women after the first trimester to aid in difficult-to-diagnose cases.[47][52][61][62]
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