creation date: 2026-01-05 14:49
tags: Pathologies
Nephrolithiasis
Background
Definitions
Nephrolithiasis, or kidney stones, refers to calculi within the kidney.
Urolithiasis refers to stones within the urinary tract which includes nephrolithiasis as well as stones within the ureters, bladder, and urethra.
Etiology
The most common causes of stones are inadequate hydration and low urine volume.
Calcium stones
Stones composed of primarily of calcium oxalate or calcium phosphate and make up of 75-85% of cases.
- Hyperparathyroidism
- Renal calcium leak
- Hypercalciuria
- Hyperoxaluria
- Hypomagnesemia
- Hypocitraturia
Uric acid stones
8-10% of cases. Associated with:
- pH <5.5
- High intake of purine-rich foods
- Cancer
- Possibly gout
Struvite stones
Made up of calcium magnesium ammonium phosphate and make up 7-8% of cases.
- Gram-negative, urease-producing organisms that break down urea into ammonia
- Psuedomonas, Proteus, Klebsiella
Cystine stones
Visually opaque and amber stones making up 1-2% of cases.
- Metabolic defect causing renal tubules to not reabsorb cystine, lysine, ornithine, and arginine
Drugs known to cause stones
- Atazanavir
- Guaifenesin
- Indinavir
- Silicate overuse
- Sulfonamide
- Triamterene
Pathogenesis
Most stones form at the junction of the nephron’s collecting tubule and the renal pelvis.
Initially a Randall plaque made up of calcium phosphate forms which acts as a nidus of which calcium oxalate layers form onto. The composition of the stone depends on the solutes which crystallize out of the urine, as such supersaturation of the urine is involved in all cases of stones.
Once the stone is formed, dilatation and spasm of the ureter and stretching of the renal capsule results in colicky pain associated with kidney stones.
Clinical Presentation
Signs & Symptoms
Stones that are smaller and in the lower pole are often asymptomatic. These are typically found incidentally.
Symptomatic stones may present as:
Pain:
- Ranges from mild/discomfort to requiring parenteral analgesics
- Waxes and wanes, develops in waves or paroxysms
- Waves typically 20-60 minutes
- Resolves with passage of stone
- Localizes to location of stone in urinary tract
Hematuria:
- Gross or microscopic
- Relatively specific with unilateral flank pain, but not sensitive
Other symptoms:
- Nausea
- Vomiting
- Dysuria and/or urinary urgency (if stone in distal ureter)
History & Physical Exam
Risk factors
Risk factors include:
- Positive family history of urolithiasis
- Prior history
- Male sex (2:1 to female)
- Diabetes, hypertension, gout, metabolic syndrome, obesity
- Increased urinary acidity (pH ≤5)
- Increased oxalate absorption
- Low urinary volume due to inadequate fluid intake
- Urinary tract infections (increases pH)
Dietary risk factors include:
- High salt intake
- High animal protein
- High oxalate foods
- Very low dietary calcium intake (increases oxalate absorption)
- Higher sugar-sweetened beverages
- Lower coffee consumption
Diagnosis
Criteria
Diagnosis of nephrolithiasis requires visualization of stones.
- CT is the gold standard
- Ultrasound and radiograph has poorer sensitivity (especially if less dense and smaller) - often requires follow-up CT if stones not identified with U/S
Work-up
Laboratory studies
- CBC
- Basic metabolic panel (glucose, calcium, electrolytes, BUN, creatinine)
- Urinalysis (for hematuria and/or concurrent UTI)
Imaging
Choice of modality depends on diagnostic accuracy weighed against radiation dose required.
- Nonpregnant adults: Low-dose noncontrast CT abdomen pelvis or kidney/bladder ultrasound
- Pregnant adults: ultrasound of kidney/bladder
Noncontrast imaging is preferred to detect hydronephrosis. CT is also capable of suggesting composition.
Differential
The flank pain associated with nephrolithiasis can also be:
- Clots from bleeding within the kidney (eg. renal cell carcinoma); note that glomerular bleeding does not lead to clot formation
- Pyelonephritis (eval: fever)
- Ectopic pregnancy (eval: ultrasound)
- Ovarian cyst rupture or torsion (eval: ultrasound)
- Dysmenorrhea (eval: onset with menses and exclusion of others)
- Intestinal obstruction, diverticulitis, appendicitis (eval: abdominal tenderness vs. flank)
- Biliary colic and cholecystitis (not associated with hematuria)
Red Flags / Complications
Persistent kidney obstruction can result in permanent kidney damage (recurrent post-renal AKI). Staghorn calculi (large renal pelvic stones that extend into the calyces) can result in kidney failure if bilaterally over time despite being asymptomatic.
If urine is infected proximal to the obstructing stone, the patient may become septic and is an emergency.
Management
Acute Management
If the patient is able to take oral medication and fluids, conservative management consist of:
- Pain medication
- Hydration
In the emergency department, this consist of:
- Ketorolac
- Prescription for oral NSAIDs (eg. ibuprofen) for subsequent attacks while awaiting stone passage
Stone passage depends on location and size of the stone. Stones ≤5 mm and more distal are likely to spontaneously pass. In patients with 5-10mm stones, medical expulsion therapy (MET) is suggested:
- Tamsulosin 0.4 mg PO once daily
- Other options: other alpha blockers, nifedipine, tadalafil
Patients should be instructed to strain urine for the stone for analysis. If stone has not passed after 4 weeks, ultrasound and radiograph should be used to assess. While more sensitive, CT is not preferred due to radiation unless the former is inadequate.
Refer to urology for patients with:
- UTI
- AKI
- Anuria
- Intractable pain, nausea, or vomiting
- Stone >10 mm in diameter
- Stone does not pass following 4 week trial of management including medical expulsive therapy, especially if stone >5 mm
Urologic intervention include:
- Shockwave lithotripsy (SWL)
- Ureteroscopy with laser lithotripsy
- Percutaneous nephrolithotomy (PNL)
- Lapsoscopic stone removal (rare)
Subsequent Management
Following stone analysis, patient should be evaluated for underlying causes of stone disease. Patients should also be educated on risk factors to avoid recurrence.