Renal, Fluids, Electrolytes & Acid-Base · Topic 6 of 22

Nephrolithiasis

Renal & GU · urolithiasis

Nephrolithiasis

Most renal colic passes with an NSAID and an alpha-blocker; an obstructing stone with infection is an emergency that needs urgent decompression.

Key numbers

Tamsulosin: distal stones ≤ 10 mm≤ 10 mm

Most stones pass; fewer when over 6 mm86% pass

01 · DoNoncontrast CT is the preferred imaging

Noncontrast CT is the preferred initial imaging: it shows stone location, degree of obstruction and alternative diagnoses. Ultrasound avoids radiation and is acceptable first-line but misses small ureteral stones without hydronephrosis.

02 · FirstObstruction plus infection: decompress urgently

A stone with obstruction and suspected infection is a urologic emergency: relieve the obstruction as soon as possible with a cystoscopic ureteral stent or percutaneous nephrostomy, treat the infection, and remove the stone later.

03 · GiveTamsulosin: distal stones ≤ 10 mm

Medical expulsive therapy: offer an alpha-blocker (tamsulosin 0.4 mg daily) for distal ureteral stones 5–10 mm; it speeds passage and reduces pain, admissions and procedures. Outpatient only if no infection, pain controlled, tolerating liquids.

Causes & risk factors

Why it happens

Most stones are calcium oxalateAbout 85% of stones contain calcium, mainly calcium oxalate; uric acid stones (5–10%) form in acidic urine (pH < 5.5); cystine stones occur only with cystinuria.

Struvite stones mean urease-producing infectionStruvite (magnesium ammonium phosphate) stones, including staghorn calculi, come from urea-splitting bacteria such as Proteus or Klebsiella; treat as infected foreign bodies and remove them completely.

Presentation

What you'll see

Renal colic: severe intermittent flank pain must knowRenal colic is excruciating, intermittent flank pain lasting 20–60 minutes, with nausea and vomiting; the patient cannot lie still. Flank pain radiating to the groin or genitals suggests a lower ureteral stone.

Diagnosis & monitoring

Work-up

Most stones pass; fewer when over 6 mmAbout 86% of stones pass spontaneously — about 90% of stones up to 6 mm but only 59% of larger stones; obstruction can still occur with small (2–5 mm) ureteral stones.

Order urinalysis, urine culture and creatinineOrder urinalysis, urine culture and serum creatinine: hematuria is common but urine can be normal; pyuria, especially with fever, suggests infection.

Do right now

In this order

First moves

Give an NSAID first for renal colic

→

Order urinalysis, urine culture and creatinine

→

Noncontrast CT is the preferred imaging

→

Obstruction plus infection: decompress urgently

Why each step

Give an NSAID first for renal colicPain relief is the first priority: an NSAID such as ketorolac 30–60 mg IM is more effective with fewer adverse effects than opioids; add an opioid (morphine, fentanyl) and an antiemetic as needed.

Order urinalysis, urine culture and creatinineOrder urinalysis, urine culture and serum creatinine: hematuria is common but urine can be normal; pyuria, especially with fever, suggests infection.

Noncontrast CT is the preferred imagingNoncontrast CT is the preferred initial imaging: it shows stone location, degree of obstruction and alternative diagnoses. Ultrasound avoids radiation and is acceptable first-line but misses small ureteral stones without hydronephrosis.

Obstruction plus infection: decompress urgentlyA stone with obstruction and suspected infection is a urologic emergency: relieve the obstruction as soon as possible with a cystoscopic ureteral stent or percutaneous nephrostomy, treat the infection, and remove the stone later.

Management

Orders

Reimage within 14 days; remove if not passedWith conservative management, reimage within 14 days to check stone position and hydronephrosis; refer for removal if the stone has not passed after about 4–6 weeks.

Extra IV fluid does not speed passageForced high-volume oral or IV hydration does not speed stone passage or relieve colic; give normal maintenance volumes.

PCNL for renal stones over 2 cmStone removal: shock wave lithotripsy for symptomatic stones < 1 cm in the kidney or proximal ureter; ureteroscopy with laser for larger or distal stones; percutaneous nephrolithotomy for renal stones > 2 cm.

The rules

Know these

Refer emergently: sepsis, anuria, solitary kidneySend for immediate urology or ED care for uncontrolled pain, suspected sepsis, anuria, bilateral obstruction, UTI with obstruction, an obstructed solitary kidney, or pregnancy.

Simple renal colic or obstructed infected kidney?

Commonly confused

Fever or sepsis	Absent
Urinalysis	Hematuria; may be normal
Disposition	Home if pain controlled, stone < 10 mm, tolerating liquids
Key move	NSAID plus tamsulosin; reimage within 14 days

Commonly confused

Tell apart

Older patient with colic: exclude aortic aneurysmIn an older patient (especially over 60 with vascular disease), a leaking abdominal aortic aneurysm or aortic dissection can mimic renal colic, including hematuria — CT also screens for it.

Teach & follow up

Patient education

Prevent recurrence: 2.5 L urine dailyFor prevention, drink enough to make at least 2.5 L of urine daily, keep normal dietary calcium, and limit sodium and animal protein; strain urine and send the stone for analysis.

More detail

Reference

Show 5 reference facts

Recurrent calcium stones: a thiazide (chlorthalidone or indapamide) lowers urinary calcium in hypercalciuria; potassium citrate treats hypocitraturia and offsets thiazide-induced hypokalemia.

Uric acid stones can be dissolved by alkalinizing the urine with potassium citrate to pH 6–6.5 plus high fluid intake; calcium stones cannot be dissolved.

After a first stone, recurrence risk is about 11% at 2 years and 39% at 15 years.

Metabolic work-up: a single calcium stone needs serum calcium to exclude hyperparathyroidism; recurrent or high-risk formers need two 24-hour urine collections (volume, pH, calcium, oxalate, uric acid, citrate, sodium).

Without infection, complete obstruction causes permanent renal damage only after about 28 days; even partial obstruction lowers GFR temporarily.

Pearl

Fever plus an obstructing stone: drain first with a stent or nephrostomy, treat the infection, and take the stone out later.

Sources · Merck Manual Professional — Urinary Calculi (2025) · Fontenelle LF, Sarti TD. Kidney Stones: Treatment and Prevention. Am Fam Physician 2019;99(8):490–496 · Merck Manual Professional — Bacterial Urinary Tract Infections (2026: catheter drainage of an obstructed infected tract) · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).