NEPHROLITHIASIS

✓ Medically ReviewedDISEASEID: MDBT0214🚨 TRIAGE: URGENTICD-10: N20.0

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Definition

CLINICAL DEFINITION

Nephrolithiasis is the formation or presence of solid concretions (calculi) within the renal pelvis or calyces, resulting from the supersaturation and crystallisation of urinary solutes such as calcium, oxalate, uric acid, and cystine.

IN PLAIN ENGLISH

Kidney stones are hard deposits made of minerals and salts that form inside the kidneys. They can cause severe pain if they move into the tubes connecting the kidneys to the bladder.

COMMON MISCONCEPTION / WHAT IT DOES NOT MEAN

Nephrolithiasis is NOT synonymous with ureterolithiasis (stones in the ureter) or cystolithiasis (bladder stones), though they share similar pathophysiological mechanisms and are collectively termed urolithiasis. It is also distinct from nephrocalcinosis, which refers to the diffuse deposition of calcium salts within the renal parenchyma rather than the collecting system.

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Word Breakdown

nephro-

=kidney (from Greek 'nephros')

lith-

=stone (from Greek 'lithos')

-iasis

=condition or process (from Greek suffix denoting disease or abnormal condition)

Literal Meaning: A condition of stones in the kidney

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Abbreviations

KUB=Kidneys, Ureters, and Bladder — standard plain radiograph for stone evaluation

SWL=Shock Wave Lithotripsy — non-invasive stone fragmentation procedure

URS=Ureteroscopy — endoscopic procedure for stone retrieval or laser lithotripsy

PCNL=Percutaneous Nephrolithotomy — minimally invasive surgical removal of large renal stones

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Synonyms & Variants

Kidney Stones›Renal Calculi›Renal Lithiasis›

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Category-Specific Context

Nephrolithiasis is a Disease characterised by the crystallisation and aggregation of urinary solutes into solid calculi within the renal collecting system. It is classified by stone composition (calcium oxalate, calcium phosphate, uric acid, struvite, cystine) and anatomical location, which dictate both acute management and long-term metabolic prevention strategies.

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Clinical Context & Usage

CLINICAL SETTINGS

Emergency DepartmentUrology ClinicNephrology ClinicGeneral PracticeInpatient Ward

USAGE & DOCUMENTATION NOTES

Clinicians frequently document 'renal colic' to describe the symptomatic presentation of a migrating stone, though nephrolithiasis refers strictly to the presence of stones in the kidney. Imaging reports often describe stone size in millimetres and location (e.g., 'lower pole', 'renal pelvis', 'ureteropelvic junction'). Measurements guide the likelihood of spontaneous passage and the need for urological intervention.

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Primary Causes & Pathophysiology

PATHOPHYSIOLOGY

Nephrolithiasis develops when the concentration of stone-forming solutes (e.g., calcium, oxalate, uric acid) exceeds their solubility in the urine, a state known as supersaturation. This leads to nucleation, where crystals form and aggregate into a solid mass. Inhibitors of crystallisation, such as citrate, magnesium, and pyrophosphate, normally prevent this process; their depletion promotes stone growth. Stones may remain asymptomatic within the renal calyces or cause severe pain (renal colic) and mucosal injury if they migrate and obstruct the urinary tract, leading to increased intraluminal pressure, capsular stretch, and ureteral spasm. Obstruction can also precipitate urinary stasis and secondary bacterial infection.

PRIMARY CAUSES

Idiopathic Hypercalciuria

Excessive renal calcium excretion despite normal serum calcium levels, leading to supersaturation of calcium oxalate or calcium phosphate.

Hyperoxaluria (Enteric or Dietary)

Increased intestinal absorption of oxalate (e.g., in fat malabsorption or high-oxalate diets) results in high urinary oxalate, strongly promoting calcium oxalate crystallisation.

Hyperuricosuria / Gout

Elevated urinary uric acid lowers the pH and provides a nidus for heterogeneous nucleation of calcium oxalate or forms pure uric acid stones in acidic urine.

Hypocitraturia

Reduced urinary citrate removes a key inhibitor of calcium crystallisation, allowing calcium salts to precipitate more readily.

Primary Hyperparathyroidism

Excess parathyroid hormone increases bone resorption and renal calcium filtration, causing hypercalcaemia and hypercalciuria.

Recurrent Urinary Tract Infections (Urease-producing bacteria)

Bacteria such as Proteus mirabilis secrete urease, which hydrolyses urea into ammonia, alkalinising the urine and precipitating magnesium ammonium phosphate (struvite) stones.

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Drug-Induced Causes

💊 Topiramate and Acetazolamide (Carbonic Anhydrase Inhibitors) ↗

Mechanism: Induce a mild metabolic acidosis and increase urinary pH while decreasing urinary citrate excretion, promoting calcium phosphate stone formation.

→ Ensure adequate hydration. Consider discontinuation or switching to an alternative agent if stones recur; potassium citrate may be used to correct hypocitraturia if the drug must be continued.

💊 Loop Diuretics (e.g., Furosemide) ↗

Mechanism: Increase renal calcium excretion by inhibiting calcium reabsorption in the thick ascending limb of the loop of Henle.

→ Discontinue if clinically feasible and switch to a thiazide diuretic, which reduces urinary calcium excretion, for patients requiring diuresis.

💊 Indinavir and other Protease Inhibitors ↗

Mechanism: The drug itself is poorly soluble in urine and precipitates to form radiolucent drug-induced calculi.

→ Increase fluid intake significantly to maintain high urine output. Consider switching to an alternative antiretroviral regimen if stones are recurrent or symptomatic.

💊 Vitamin D and Calcium Supplements (Excessive dosing) ↗

Mechanism: Excessive intake can lead to hypercalciuria and supersaturation of calcium salts, particularly if taken without food.

→ Review supplement necessity and dosage. Ensure calcium supplements are taken with meals to bind dietary oxalate in the gut, reducing oxalate absorption.

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Epidemiology

Prevalence:The lifetime prevalence of nephrolithiasis is approximately 10–15% in developed countries, with a rising global incidence over the past few decades. It is more common in industrialised nations, likely linked to dietary factors, obesity, and metabolic syndrome.

Age Group:Peak incidence occurs in adults aged 30–60 years. It is relatively uncommon in children, though paediatric cases are increasing, often associated with metabolic anomalies or anatomical abnormalities.

Sex Predilection:Male

Geographic Distribution:Higher prevalence is observed in the 'Stone Belt' of the southeastern United States, as well as in regions with hot, arid climates where chronic mild dehydration is common. Incidence is also rising globally in parallel with Westernised diets and increasing rates of obesity.

Red Flags & Triage ★

TRIAGE LEVEL

🚨 URGENT

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

Obstructed infected kidney (pyonephrosis) — presents with renal colic, fever, and systemic toxicity; requires immediate urological consultation for emergency decompression via ureteric stent or percutaneous nephrostomy to prevent fatal urosepsis.
Solitary kidney with obstruction — an obstructing stone in a patient with a single functioning kidney constitutes acute renal failure and requires urgent decompression to preserve renal function.

URGENT EVALUATION TRIGGERS

Fever, rigors, or haemodynamic instability in the presence of an obstructing stone — indicates infected hydronephrosis
Intractable pain or persistent vomiting unresponsive to standard emergency department analgesia and antiemetics
Acute kidney injury (rising serum creatinine) or anuria, particularly in bilateral obstruction or a solitary kidney
Stone size >10 mm with no signs of spontaneous passage or failure of medical expulsive therapy after 4 weeks

Contraindications & Precautions

SPECIAL PRECAUTIONS

Avoid prescribing NSAIDs in patients with pre-existing chronic kidney disease
volume depletion
or concurrent nephrotoxic drug use due to the risk of acute kidney injury.
Do not delay decompression (stent or nephrostomy) in a patient with an obstructed
infected kidney
regardless of stone size or location.
Use caution with opioid analgesics in elderly patients or those with respiratory compromise; monitor for sedation and respiratory depression.

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Acute Kidney Injury (AKI) — post-renal obstruction causing elevated intratubular pressure and reduced glomerular filtration rate
Urosepsis and Pyonephrosis — infected obstructed kidney leading to systemic inflammatory response and potential renal parenchymal destruction
Chronic Kidney Disease (CKD) — recurrent obstruction
infection
and repeated surgical interventions causing cumulative nephron loss
Ureteral Stricture — chronic inflammation and mucosal injury from impacted stones or repeated endoscopic procedures leading to fibrotic narrowing

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Confused With (LASA & DDx) ★

LEXICAL (LASA) — SIMILAR NAMES

Nephrocalcinosis

Sounds similar and involves renal calcium; however, nephrocalcinosis refers to diffuse calcium deposition within the renal parenchyma (tissue), whereas nephrolithiasis refers to discrete stones within the collecting system (urinary tract).

Cholelithiasis

Shares the '-lithiasis' suffix; cholelithiasis refers to gallstones in the biliary system, which can present with right-sided abdominal pain that must be differentiated from right-sided renal colic.

CLINICAL DIFFERENTIAL DIAGNOSES (DDx)

Acute Appendicitis

Key Distinguishing Feature: Right lower quadrant pain with peritoneal signs, fever, and anorexia; imaging shows an inflamed appendix rather than a urinary tract calculus.

Ovarian Torsion or Ruptured Ectopic Pregnancy

Key Distinguishing Feature: Pelvic pain in females of reproductive age; transvaginal ultrasound and beta-hCG testing differentiate gynaecological emergencies from urological colic.

Biliary Colic / Acute Cholecystitis

Key Distinguishing Feature: Right upper quadrant pain radiating to the right scapula, often postprandial; ultrasound shows gallstones or gallbladder wall thickening, with normal renal imaging.

Abdominal Aortic Aneurysm (AAA) Rupture or Leak

Key Distinguishing Feature: Severe back or flank pain in older adults with cardiovascular risk factors; may present with hypotension and a pulsatile mass. Requires immediate CT angiography.

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Clinical Pearls

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A non-contrast CT KUB is the gold standard imaging modality for suspected nephrolithiasis, offering near 100% sensitivity and specificity. Ultrasound is preferred as the initial imaging choice in pregnant women and children to avoid ionising radiation.

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Medical expulsive therapy (MET) with alpha-blockers like tamsulosin is most effective for distal ureteral stones between 5 and 10 mm. It provides little to no benefit for stones <5 mm (which pass spontaneously) or >10 mm (which rarely pass).

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The presence of 'staghorn calculi' filling the renal pelvis and calyces is almost always associated with chronic infection by urease-producing bacteria (struvite stones). These require complete surgical removal, as leaving fragments behind guarantees rapid recurrence and progressive renal destruction.

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Thiazide diuretics are the mainstay of pharmacological prevention for recurrent calcium stones associated with hypercalciuria. They work by enhancing calcium reabsorption in the distal convoluted tubule, thereby reducing urinary calcium supersaturation.

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Example Usage & SOAP

CLINICAL SENTENCE

"A 45-year-old male presented to the Emergency Department with sudden-onset, severe left flank pain radiating to the groin; non-contrast CT revealed a 6 mm obstructing calculus at the left ureterovesical junction with mild proximal hydroureteronephrosis."

IN A SOAP NOTE

S: 38-year-old female complains of acute right-sided flank pain starting 4 hours ago, associated with nausea and one episode of vomiting. Pain is colicky and radiates to the right groin. O: Vitals: BP 145/85, HR 102, Temp 37.1°C. Abdomen soft, non-tender, but marked right costovertebral angle tenderness is present. Urinalysis: 3+ blood, negative leukocyte esterase and nitrites. P: CT KUB performed showing a 4 mm radiopaque stone in the distal right ureter with mild hydronephrosis. Serum creatinine is normal at 0.8 mg/dL. A: Right distal ureterolithiasis with renal colic, uncomplicated by infection or acute kidney injury. P: Discharged with PRN diclofenac for pain, tamsulosin 0.4 mg daily for medical expulsive therapy, and a urine strainer. Advised to return immediately if fever, intractable pain, or inability to tolerate oral fluids develops. Outpatient urology follow-up in 2 weeks.

DIFFERENTIAL DIAGNOSIS CONTEXT

Differential for acute flank pain: (1) Nephrolithiasis/Renal Colic — sudden onset, colicky, radiating to groin, accompanied by microscopic haematuria. (2) Pyelonephritis — constant flank pain with fever, systemic symptoms, and positive urinary nitrites/leukocyte esterase. (3) Musculoskeletal pain — reproducible with movement or palpation, lacks autonomic symptoms like nausea or haematuria. (4) Ruptured AAA — older patient, tearing back pain, hypotension, pulsatile abdominal mass.

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Prognosis

SHORT-TERM OUTCOME

Most small, uncomplicated stones (<5 mm) pass spontaneously within 4 weeks with adequate analgesia and hydration. Acute renal colic typically resolves rapidly once the stone passes or is surgically removed.

LONG-TERM PROGNOSIS

The recurrence rate is high, approximately 50% within 5–10 years without targeted metabolic prevention. Long-term prognosis for renal function is generally excellent for unilateral stones, but recurrent bilateral stones or chronic obstruction can lead to progressive CKD.

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References & Coding

ICD-10 DIAGNOSTIC CODE

N20.0

LITERATURE CITATIONS & GUIDELINES

[1]Pearle MS, Goldfarb DS, Assimos DG, et al. Medical management of kidney stones: AUA guideline. J Urol. 2014;192(1):13-21. doi:10.1016/j.juro.2014.05.006

[2]European Association of Urology (EAU). Guidelines on Urolithiasis. 2023.

[3]Worcester EM, Coe FL. Clinical practice. Calcium kidney stones. N Engl J Med. 2010;363(10):954-963. doi:10.1056/NEJMcp1000027

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