Urology & Nephrology
Kidney stones - Renal lithiasis
Kidney stones - also known as urinary lithiasis or «kidney stones» in everyday language - are solid concretions formed in the upper urinary tract (calyces, renal pelvis) by the precipitation and crystallization of mineral or organic substances normally dissolved in urine. Urinary lithiasis is a very common pathology: it affects around 10 to 15 % of the Canadian population over the course of a lifetime, with prevalence rising steadily since the 1970s, in connection with the Western diet (hypercaloric, rich in animal proteins and salt), sedentary lifestyle, obesity and climate change (dehydration linked to rising temperatures). The recurrence rate is high - 50 % at 5 years and 75 % at 20 years without prevention - making urinary lithiasis a chronic disease requiring long-term metabolic and preventive management after a first episode. Urinary calculi differ from gallstones (vesicular lithiasis) in their location, composition and management - although the two conditions are often confused in common parlance. The majority of kidney stones remain silent as long as they remain in the renal cavities - they only become symptomatic when they migrate into the ureter and cause obstruction, manifesting as renal colic. Management is based on three complementary principles: treatment of the acute phase (analgesia, encouraging spontaneous expulsion), urological management of stones requiring intervention, and prevention of recurrence through targeted nutritional and medicinal measures depending on the composition of the stone.
Types of calculations and composition
| Type of calculation | Frequency | Radiopacity | Risk factors and context |
|---|---|---|---|
| Calcium oxalate monohydrate (whewellite) | 35–40 % | Radiopaque | Idiopathic hypercalciuria, hyperoxaluria (dietary or primary), hypocitraturia, chronic dehydration; very hard stones—resistant to extracorporeal shockwave lithotripsy (ESWL). |
| Calcium oxalate dihydrate (weddellite) | 35–45 % | Radiopaque | Hypercalciuria; more friable than whewellite — better response to ECR; often associated with a diet rich in oxalates (spinach, rhubarb, nuts, chocolate) |
| Uric acid | 5-10 % | Radiotransparent | Chronic acidic urine (pH < 5.5), hyperuricemia (gout, metabolic syndrome, type 2 diabetes), chemotherapy (lysis syndrome), diet rich in purines; the only type of stone that can be dissolved by urine alkalization (medical treatment) |
| Calcium phosphate (apatite, brushite) | 5-8 % | Very radiopaque | Distal renal tubular acidosis (urinary pH constantly > 6.0), primary hyperparathyroidism, hypercalciuria with alkaline urine; brushite - very hard, resistant to ESWL |
| Struvite (magnesium ammonium phosphate) | 2–5 % | Radiopaque | Recurrent urinary tract infections with urease-positive bacteriaProteus mirabilis, Klebsiella, Pseudomonas; coraliform calculations mold renal cavities; almost exclusively in women; risk of renal destruction if untreated |
| Cystine | 1–2 % | Slightly radiopaque | Hereditary cystinuria (autosomal recessive) - defect in tubular reabsorption of cystine, ornithine, lysine, arginine (COLA); first stone often before 20 years of age; multiple recurrences throughout life; yellowish stones with «frosted glass» appearance on CT scan |
General risk factors
- Chronic dehydration: a universal risk factor — insufficient diuresis (<1.5 L/day) concentrates all lithogenic solutes; exposed occupations (hot environment workers, firefighters, cooks), residence in hot regions, intensive sports practice without sufficient hydration compensation; urine should be clear to pale yellow — dark urine indicates insufficient hydration
- High intake of animal proteins: red meat, charcuterie, seafood — increases the urinary acid load (lower pH → uric acid precipitation), urinary calcium and oxalate excretion, and reduces calciuria (natural inhibitor of crystallization); hypercaloric Western diet — major explanatory factor for the increasing prevalence.
- High salt (sodium) diet: Idiopathic hypercalciuria is largely sodium-dependent — renal sodium excretion is accompanied by a parallel urinary calcium leak; 2 g/day sodium reduction → 50 to 100 mg/day calciuria reduction
- Oxalate-rich diet: spinach, rhubarb, beet, walnuts, almonds, dark chocolate, black tea, wheat bran - foods with very high oxalate content; limit but do not eliminate (dietary calcium taken at the same time as the meal chelates oxalate in the intestine, reducing its absorption).
- Low calcium intake (paradox): Contrary to intuition, a diet low in calcium increases the risk of calcium oxalate stones — in the absence of dietary calcium in the intestine, oxalate is absorbed in greater quantities by the intestinal lining → hyperoxaluria → precipitation in the urine; recommendation: normal dietary calcium (1,000–1,200 mg/day); calcium supplements taken between meals increase the risk (no intestinal chelation).
- Obesity and metabolic syndrome: hyperinsulinism → urine acidification (pH < 5.5) → risk of uric acid stones; hypercalciuria associated with obesity; insulin resistance → reduced calciuria; management of metabolic syndrome directly reduces stone risk
- Predisposing pathologies: primary hyperparathyroidism (hypercalcemia → hypercalciuria); gout (hyperuricemia → uric acid stones); Crohn's disease and ileal resections (intestinal hyperabsorption of oxalate - enterogenic oxaluria); bariatric surgery (gastric bypass - post-bypass hyperoxaluria due to fat malabsorption); horseshoe kidney (anatomical anomaly → urinary stasis); medullary sponge kidney (ectatic collecting tubules); type 1 renal tubular acidosis
- Genetic factors: first-degree family history → risk multiplied by 2 to 3; hereditary cystinuria; primary hyperoxaluria type 1 (hepatic alanine-glyoxylate aminotransferase - AGXT - deficiency); xanthinuria
ℹ️
Kidney stones are distinct from gallstones (gallbladder or bile duct stones): they form in different organs, have different compositions, and are treated differently. A kidney stone typically causes flank pain that radiates to the groin (renal colic) accompanied by hematuria, whereas a gallstone causes pain in the right hypochondrium (right side under the ribs) that radiates to the right shoulder after a fatty meal, without hematuria.
Symptoms
- Silent intrarenal stones: The vast majority of stones in the renal cavities (calyces or renal pelvis) remain asymptomatic for months to years and are discovered incidentally during an abdominal ultrasound or CT scan performed for another indication; their size can gradually increase without symptoms until they migrate into the ureter.
- Renal colic (ureteral stone): acute unilateral lumbar pain of maximal intensity radiating along the ureteral path towards the iliac fossa, groin, and external genitalia; paroxysmal, with no relieving posture (the patient is agitated, writhing in pain—unlike peritoneal pain where the patient is immobile); nausea and reflex vomiting in 50–60 % of cases; microscopic or macroscopic hematuria in 85 % of cases
- Isolated hematuria: incidental finding of microscopic hematuria (on dipstick or urinalysis) without associated symptoms — may reveal a silent intrarenal stone or a small, minimally obstructive ureteral stone; always investigate hematuria, even isolated, to rule out a urological tumor
- Recurrent urinary tract infection on struvite stone: recurring urinary tract infections Proteus mirabilis or other urease-positive germs, sometimes with recurrent pyelonephritis; struvite stones serve as a bacterial reservoir—the infection promotes stone growth, and the stone promotes infection
- Silent chronic kidney disease: recurrent bilateral stones (cystinuria, primary hyperoxaluria), staghorn calculi progressively obstructing the renal cavities, or unrecognized chronic hydronephrosis can lead to insidious CKD discovered late.
Diagnostic and metabolic assessment
- Abdomino-pelvic scanner without injection (uro-CT): reference examination for diagnosis—sensitivity 96–99 %, specificity 95–99 %; localizes the stone, measures its size (mm), assesses its density in Hounsfield units (HU—predictive of composition and friability), and quantifies the degree of obstruction (hydronephrosis, ureteronephrosis); uric acid stones are radiolucent on KUB but visible on CT (density 200–500 HU); cystine stones have intermediate density (400–600 HU)
- Urinary tract ultrasound: first-line in pregnant women (avoiding radiation) and children; lower sensitivity than CT for small ureteral stones (45–70 %) but excellent for detecting hydronephrosis; useful for monitoring known kidney stones without acute colic
- Analysis of expelled or extracted stones (IRTF): essential for guiding relapse prevention — asking the patient to filter their urine (coffee filter, gauze) to retrieve the stone; Fourier Transform Infrared Spectrometry (FTIR) — reference method; X-ray crystallography
- Urinary and blood metabolic panel (after first episode or early recurrence): 24-hour urine - calciuria (normal < 6.25 mmol/day H, < 5 mmol/day F), oxaluria (normal 1.7 mmol/day - crystallization inhibitor), uricuria, phosphaturia, creatininuria, urinary sodium, urinary volume (target > 2 L/day); urinary pH on 3 morning fasting samples (pH 6.5 → struvite or ATR type 1); blood: creatinine and GFR, calcemia, phosphatemia, uricemia, intact parathyroid hormone (PTH) (hyperparathyroidism), 25-OH vitamin D, bicarbonates; urinary amino acid electrophoresis if cystinuria suspected (sodium nitroprusside test - positive if cystinuria)
Treatment and prevention of recurrence by stone type
| Type of calculation | Preventive measures and specific treatments |
|---|---|
| Calcium oxalate (any type) | Hydration: diuresis > 2.0–2.5 L/day (universal goal — most effective measure for all stones combined); normal dietary calcium 1,000–1,200 mg/day with meals (chelates intestinal oxalate); reduce extreme dietary oxalates; reduce animal protein (< 1 g/kg/day); reduce salt (< 5 g NaCl/day); if persistent hypercalciuria despite measures: hydrochlorothiazide 25 mg/day or chlorthalidone 25 mg/day (reduce calciuria by 40–50 %); if hypocitraturia: potassium citrate 20–40 mEq/day (alkalinizes urine, inhibits calcium crystallization) |
| Uric acid | Urine alkalization — target urinary pH 6.0–6.5: potassium citrate 20–60 mEq/day in 3 doses or sodium bicarbonate 3–6 g/day; uric acid stones can dissolve completely with medical alkalization (chemolysis — the only type of medically dissolvable stone); reduction of dietary purines (red meat, offal, beer); allopurinol 300 mg/day if persistent hyperuricemia (> 480 µmol/L); treatment of metabolic syndrome |
| Calcium phosphate (apatite) | Abundant hydration; treatment of renal tubular acidosis type 1 (potassium citrate — alkalizes urine and provides citrate); surgery if primary hyperparathyroidism (parathyroidectomy — lithiasis cured in 90 % of cases); reduce salt and animal protein |
| Struvite | Prolonged antibiotic treatment targeting urease-positive bacteria (guided urine culture); complete surgical removal of all fragments (PNL + ureteroscopy) — essential as residual fragments are a permanent infectious focus maintaining stone growth; acetohydroxamic acid (inhibitor of bacterial urease) — effective but poorly tolerated (nausea, headaches, thrombosis); urine acidification (ascorbic acid) — poorly effective and not recommended for routine use |
| Cystine | Very intensive hydration: diuresis of > 3 L/day mandatory (to dilute cystine below its solubility); intense urinary alkalinization: potassium citrate for a target pH > 7.5 (cystine solubility increases exponentially at pH > 7.0); D-penicillamine (cystine chelator — very effective but significant toxicity: nephrotoxicity, thrombocytopenia, induced lupus); tiopronin (Thiola — α-MPG) — less toxic than D-penicillamine, preferred as a first-line chelator; captopril (ACE inhibitor — forms soluble cystine-captopril complexes) — limited data |
Urologic interventions
- Expulsion spontanée et traitement médical expulsif : calculs ≤ 5 mm — taux d'expulsion spontanée 60–80 % en 4 semaines ; calculs 5–10 mm — 40–60 % avec traitement médical expulsif ; tamsulosine (Flomax) 0,4 mg/jour — alpha-1 bloquant relaxant la musculature lisse urétérale distale ; calculs > 10 mm — expulsion spontanée < 10 % — intervention urologique quasi systématique
- Extracorporeal shock wave lithotripsy (ESWL): kidney or proximal ureteral stones ≤ 20 mm; CT density < 900 HU (very dense stones—whewellite, brushite, cystine—are resistant); no complete obstruction; contraindications: pregnancy, bleeding disorders, pacemaker, aortic aneurysm, stone on a single kidney without an available urologist
- Flexible ureteroscopy (FURS) with holmium laser: ureteral stones of any size; renal stones ≤ 15–20 mm; treatment of choice for radiolucent uric acid stones (well fragmented by laser); treatment of choice if ESWL is contraindicated
- Percutaneous Nephrolithotomy (PCNL): kidney stones > 20 mm; staghorn (struvite) stones; failure of ESWL or URS; lower pole stones > 15 mm difficult to drain by PCNL; mini-PCNL (Mini-PCNL) technique reducing bleeding
- Double-J stent (ureteral stent): Emergency internal drainage for febrile nephritic colic (infected obstruction - pyonephrosis) or obstruction of a single kidney; can be left in place for 4 to 6 weeks during planned lithotripsy
Feverish calculation - absolute emergency: dial 911
Dial 911 Go immediately to the emergency room if severe lower back pain is accompanied by fever (> 38.5°C) and chills—this indicates an infected urinary obstruction (pyonephrosis) requiring urgent urinary drainage (Double-J stent or percutaneous nephrostomy) and IV antibiotics. Without rapid drainage, the risk of septic shock and irreversible kidney destruction is significant. Also, go to the emergency room if the pain is refractory to usual painkillers, or if you have a single kidney, a kidney transplant, or are currently pregnant.
For metabolic assessment, relapse prevention, and interpretation of imaging or stone analysis results, Clinique Omicron physicians will guide you and coordinate your urological care. Consultations are available at our service points in Quebec as well as through telemedicine. To book an appointment, visit cliniqueomicron.ca.
Consult at Clinique Omicron
Clinique Omicron manages uncomplicated urinary stones, prescribes urinary CT scans and complete metabolic stone workups (24-hour urine collection, hormonal profile, stone analysis), initiates expulsion treatment and recurrence prevention measures tailored to the stone type, and refers to partner urologists for stones requiring intervention. Consultations are available at our service points in Quebec as well as through telemedicine. To book an appointment, visit cliniqueomicron.ca.
The content of this page is for informational purposes only and does not substitute for the advice of a qualified healthcare professional. Any febrile kidney stone is a urological emergency requiring immediate hospitalization.
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