Investigations

1st investigations to order

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Microhaematuria is seen in the majority of patients with renal stones.

Result

may be normal; dipstick positive for leukocytes, nitrates, blood; microscopic analysis positive for WBCs, RBCs, or bacteria

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A raised WBC may suggest infection (pyelonephritis or urinary tract infection).

Result

variable

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These include sodium, potassium, chloride, bicarbonate, creatinine, urea, calcium, uric acid, and phosphorus.

Hypercalcaemia may suggest hyperparathyroidism as an underlying aetiology; hyperuricaemia may indicate gout.

Result

variable

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Prior to exposure to ionising radiation.

To exclude ectopic pregnancy.

Result

negative

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Non-contrast helical computed tomography scan (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.

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. However, low-dose computed tomography (CT) is not recommended for those with a BMI >30 kg/m², owing to lower sensitivity and specificity in these patients.[31] 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.[42]

NCCT accurately determines presence, size, and location of stones; if negative, nephrolithiasis can be ruled out with high likelihood.

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.[37][38][31][39]

Result

calcification seen in renal collecting system or ureter; hydronephrosis; perinephric stranding (indicative of inflammation or infection)

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Provides information on chemical composition and aetiology. Stones are analysed after they are extracted during surgery or when patients expel and collect them for analysis.

Result

stone composition

Investigations to consider

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Plain abdominal film could be ordered initially along with computed tomography (CT) scan to determine whether stone is radiolucent. Up to 85% of stones are visible on KUB, although uric acid stones are radiolucent.[43]

A KUB x-ray should be performed if the stone is not visible on a CT scout, so that patients with stones identifiable on initial KUB x-ray or CT scout can be followed by KUB.[31]

Before definitive surgical therapy, a KUB should be ordered in an asymptomatic patient to ensure that patient has not already passed the stone.

Result

calcification seen within urinary tract

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In pregnancy, renal ultrasound is the first-line imaging modality. It should also be the modality of choice when there is a desire to reduce or eliminate radiation exposure, such as for evaluation of children. Low-dose computed tomography (CT) can be considered in children if renal ultrasound is non-diagnostic.[31]

Result

calcification seen within urinary tract, along with dilation

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This test has for the most part been replaced by the computed tomography (CT) scan (the new diagnostic standard) for the evaluation and diagnosis of renal stones; however, it is still useful to assess renal function and collecting system drainage.

Result

calcification seen within urinary tract or a filling defect seen when dye is passing through the kidney and down the ureter

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Although conferring no radiation to the patient, MRI 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. It can help to define the level of urinary tract obstruction.[38]

Result

filling defect seen in the collecting system

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Helps in determining underlying metabolic cause or aetiology for nephrolithiasis. Should be ordered once the patient is stone free.

Basic measurements should include volume, pH, creatinine, sodium, calcium, oxalate, uric acid, and citrate.

Patients with recurrent renal stones should have subsequent periodic 24-hour urine monitoring.

Result

increased or decreased values for urinary electrolytes; reduced urine volume

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A urine screen for cystine should be considered if the diagnosis of cystinuria is not excluded by stone analysis.

Result

cystinuria

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