Top ten tips – renal and ureteric stones

1. CT of the kidneys, ureter and bladder (KUB) is the gold standard investigation for ureteric stones

Non-contrast CT is the gold standard investigation for patients with acute pain and suspected ureteric stones. CT KUBs are more accurate than intravenous urograms (IVU). They also have other benefits including speed of the test, detection of other pathology, and eliminating risks of intravenous contrast (nephrotoxicity and anaphylaxis). Imaging should be organised within seven days but sooner where possible. The finding of a ureteric stone should prompt an urgent urology outpatient opinion. If non-obstructing renal stones are identified, this should be followed up with a routine referral. If no stones are identified, stone passage may have occurred but an alternative diagnosis must be considered.

Ultrasonography is good at identifying renal stones larger than 5mm and can be used to diagnose hydronephrosis, which may be an indication of a ureteric stone.

2. Dipstick haematuria is not present in all patients with ureteric colic

Some 20% of patients with ureteric stones do not have dipstick haematuria, and therefore the absence of dipstick haematuria does not rule out a ureteric or renal stone.¹ Urine dipstick may suggest other pathology such as UTI.

3. Beware abdominal aortic aneurysm as an alternative diagnosis

Acute loin or ‘loin to groin’ pain may have several causes.

A thorough history and examination is important. A leaking abdominal aortic aneurysm may mimic ureteric colic and patients at high risk (for instance, an arteriopath over 60 years) require immediate referral for imaging.

4. Infection and stones don’t mix

An infected, obstructed kidney is a urological emergency requiring urgent drainage. If you suspect a stone and there are any signs of infection (fever, rigors, positive nitrites on urinalysis) refer the patient for immediate urological assessment.

5. Diagnostic uncertainty is an indication for acute hospital admission

So too are:

• uncontrolled pain

• fever (>37.5°C) in association with suspected ureteric colic

• renal or ureteric colic in a patient with a solitary or transplanted kidney

• suspected bilateral ureteric stones

• derangement in renal function with suspected ureteric colic.

Also refer if there is difficulty arranging prompt outpatient assessment.

6. The immediate management of a patient with acute ureteric colic is analgesia

First-line analgesia should be NSAIDs.² They achieve better pain control with fewer side-effects than opiates in patients with ureteric colic. As these patients often vomit, rectal administration is best and has rapid absorption. If there are no contraindications, we use 100mg diclofenac PR with opiates as second line.³

7. More than 80% of stones <4mm in size pass spontaneously within four to six weeks

Patients with small ureteric stones without infection or renal impairment can be reassured that it is likely that their stone will pass. It is important to confirm that the stone has passed with follow-up imaging unless the patient sees it happen.

An outpatient referral to a urology service is required so that the patient can be seen within four weeks and appropriate treatment provided if the stone fails to pass.

8. Consider medical expulsive therapy

α-blockers (such as tamsulosin) can increase the likelihood of spontaneous stone passage by up to 65%. They have also been shown to reduce time to expulsion, pain episodes and analgesic requirements. It is currently an ‘off-label’ indication but the evidence is good and most guidelines advocate the use of α-blockers.

Patients should be warned of the side-effects and women should be advised to use contraception while taking the drug.

9. There is no evidence that ‘flushing out’ a kidney stone works

Although a good fluid intake is important (see below), patients should not be asked to drink excessively to try to ‘flush out’ an existing stone. There is no evidence to suggest that this works.

10. Consider prevention

All first-time stone formers should have a limited metabolic evaluation consisting of renal function, serum calcium and urate.

Dietary interventions that can reduce stone growth or recurrence include:

• increased fluid intake with a target urine output of more than 2l/day

• reduced salt (less than 2300mg sodium/day)

• reduced animal protein (no more than two meals daily with less than eight ounces/day)

• moderate calcium intake (1000 to 1200mg/day)

• reduced consumption of high-oxalate foods (such as spinach, strawberries, nuts, rhubarb, dark chocolate, cocoa, brewed tea)

• increased intake of citrate-rich fluids (for instance, real lemonade, orange juice).

Mr Matthew Bultitude is a consultant urological surgeon and Ms Archana Fernando is a ST5 urology registrar at Guys and St Thomas’ Hospital, London

References