Investigations
1st investigations to order
urinalysis
Test
Microhaematuria is seen in the majority of patients with renal stones.[49]
Result
may be normal; dipstick positive for leukocytes, nitrates, blood; microscopic analysis positive for WBCs, RBCs, or bacteria
FBC and differential
Test
A raised WBC may suggest infection (pyelonephritis or urinary tract infection).
Result
variable
serum electrolytes, urea, and creatinine
Test
These include calcium, sodium, potassium, chloride, bicarbonate, creatinine, urea, uric acid, and phosphorus.[47]
Hypercalcaemia may suggest hyperparathyroidism as an underlying aetiology; hyperuricaemia may indicate gout.
Result
variable
urine pregnancy test
Test
Request in women of childbearing age prior to exposure to ionising radiation and to exclude ectopic pregnancy.
Result
negative
non-contrast helical CT scan (nonpregnant adult)
Test
Request an urgent (within 24 hours of presentation) low-dose non-contrast computed tomography (NCCT) scan for any nonpregnant adult patient with suspected renal colic.[16]
NCCT is the preferred imaging modality for nephrolithiasis due to its high sensitivity and specificity, and should be ordered as soon as nephrolithiasis is suspected. NCCT accurately determines presence, size, and location of stones; if negative, nephrolithiasis can be ruled out with high likelihood.
A low-dose scan (<4 mSv) is preferred for patients with a body mass index (BMI) ≤30 kg/m², as this imaging study limits the potential radiation exposure while maintaining both sensitivity and specificity at 90% or higher. Low-dose CT is not recommended for those with a BMI >30 kg/m², owing to lower sensitivity and specificity in these patients.[52] A size-adjusted, reduced-dose CT protocol has been shown to be 96% sensitive for the detection of ureteral stones requiring intervention in all patients, regardless of BMI.[65]
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 used as a last-line option in pregnant women after the first trimester to aid in difficult-to-diagnose cases.[47][52][61][62]
Consider low-dose NCCT if the patient is aged under 16 years and the diagnosis remains uncertain after ultrasound.[16][47][52]
Result
calcification seen in renal collecting system or ureter; hydronephrosis; perinephric stranding (indicative of inflammation or infection)
renal ultrasound (pregnant or child)
Test
If the patient is pregnant or under 16 years of age, request an urgent (within 24 hours of presentation) renal ultrasound.[16][47][53]
In children and young people, consider low-dose NCCT if the diagnosis remains uncertain after ultrasound.[16][47][52]
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.
Result
calcification seen within urinary tract, along with dilation
Investigations to consider
stone analysis
Test
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.
Result
stone composition
plain abdominal radiograph (KUB)
Test
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.
Result
calcification seen within urinary tract
MRI
Test
Although conferring no radiation to the patient, MRI is a second-line imaging modality in pregnant women because stones are not directly visible on MRI and only seen as a filling defect in the collecting system. It can help to define the level of urinary tract obstruction.[47]
Result
filling defect seen in the collecting system
spot urine for cystine
Test
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 with large or recurrent stones.[3]
Result
cystinuria
Emerging tests
dual-energy CT
Test
Dual-energy CT 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]
Result
visualisation of uric acid stones
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