[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Kidney](https://durgical.com/en/general-pathology/areas/kidney/) › Kidney stones

# Kidney stones

- Lesion

Supersaturated urine lets salts crystallize into stones that obstruct, bleed and infect; calcium stones are most common.

Updated Nov 12, 2026

## Key points

- Calcium oxalate (with or without phosphate): about four fifths; hypercalciuria (absorptive, renal, or from hypercalcemia), hyperoxaluria, hyperuricosuria, hypocitraturia.
- Struvite (magnesium ammonium phosphate): Proteus and other urease producers; alkaline urine; staghorn stones.
- Uric acid: acid urine, gout, tumour lysis; radiolucent on plain films.
- Cystine: cystinuria (defective reabsorption of cystine, ornithine, lysine, arginine); hexagonal crystals; begins in youth.
- Low fluid intake and hot climates raise the risk; enteric hyperoxaluria after bowel disease or resection.

## What it is

Stones form when urine becomes supersaturated with a salt, when inhibitors of crystallization (citrate, pyrophosphate, uromodulin) are low, or when urine pH favours precipitation. Most are calcium oxalate, often with hypercalciuria; struvite stones form around urease-producing bacteria in alkaline urine and can grow into staghorn casts of the pelvis; uric acid stones form in acid urine with high urate; cystine stones come from an inherited transport defect. Stones are usually unilateral and form in the calyces and pelvis.

## Structure

- Stones range from sand to large branched casts of the pelvis and calyces (staghorn).
- Small stones pass into the ureter and lodge at narrow points: the ureteropelvic junction, the pelvic brim and the vesicoureteral junction.
- The kidney may show hydronephrosis, pyelonephritis and scarring.

## Kidney stones

| Stone | Setting | Urine pH | Clue |
| --- | --- | --- | --- |
| Calcium oxalate or phosphate | Idiopathic hypercalciuria, hyperparathyroidism, enteric hyperoxaluria | Oxalate: any; phosphate: alkaline | Radiopaque; envelope or dumbbell crystals |
| Struvite | Infection with urease-producing bacteria (Proteus) | Alkaline | Staghorn stones, recurrent infection; coffin-lid crystals |
| [Uric acid](https://durgical.com/en/conditions/gout/) | Gout, tumour lysis, acid urine, metabolic syndrome | Acid | Radiolucent on plain films; rhomboid crystals |
| [Cystine](https://durgical.com/en/conditions/cystinuria/) | Cystinuria (inherited) | Acid | Hexagonal crystals, stones from childhood or youth |

## Clinical notes

- Renal colic radiating from flank to groin, with hematuria; obstruction plus infection is an emergency.
- Recurrent stones call for a metabolic study of urine and blood, including calcium and parathyroid hormone.

## Memory aid

Calcium is common, struvite is infected, uric acid is invisible, cystine is hexagonal.

## Test yourself

Think of the answer, then tap the question to see it.

## Which stone forms in alkaline urine infected by Proteus?

Struvite (magnesium ammonium phosphate), often a staghorn stone.

## Which stones are radiolucent on plain radiographs?

Uric acid stones.

## What is the most common metabolic abnormality in calcium stone formers?

Hypercalciuria, usually without hypercalcemia.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/kidney-stones/)

[More Pathology questions →](https://durgical.com/en/practice/?f=pathology)

## Elsewhere in DurgiPedia

- [Uric acid](https://durgical.com/en/biochemistry/molecules/uric-acid/)
- [Pathologic calcification: dystrophic vs metastatic](https://durgical.com/en/general-pathology/pathologic-calcification-dystrophic-vs-metastatic/)

## Connections

## Related 4

- [Crystal nephropathies and nephrocalcinosis](https://durgical.com/en/general-pathology/crystal-nephropathies-and-nephrocalcinosis/)
- [Urinary tract obstruction and hydronephrosis](https://durgical.com/en/general-pathology/urinary-tract-obstruction-and-hydronephrosis/)
- [Acute pyelonephritis](https://durgical.com/en/general-pathology/acute-pyelonephritis/)
- [Pathologic calcification: dystrophic vs metastatic](https://durgical.com/en/general-pathology/pathologic-calcification-dystrophic-vs-metastatic/)

## Related conditions 8

- [Kidney stones (urolithiasis)](https://durgical.com/en/conditions/kidney-stones/)
- [Cystinuria](https://durgical.com/en/conditions/cystinuria/)
- [Primary hyperparathyroidism](https://durgical.com/en/conditions/primary-hyperparathyroidism/)
- [Gout](https://durgical.com/en/conditions/gout/)
- [Primary hyperoxaluria](https://durgical.com/en/conditions/primary-hyperoxaluria/)
- [Hypercalcaemia](https://durgical.com/en/conditions/hypercalcaemia/)
- [Medullary sponge kidney and medullary cystic disease](https://durgical.com/en/conditions/medullary-sponge-kidney-and-medullary-cystic-disease/)
- [Crohn disease](https://durgical.com/en/conditions/crohn-disease/)

## Microorganisms 1

- [Proteus mirabilis](https://durgical.com/en/microbiology/proteus-mirabilis/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Renal Calculi, Nephrolithiasis](https://www.ncbi.nlm.nih.gov/books/NBK442014/) (StatPearls (NCBI Bookshelf), 2024); [Cystinuria: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/cystinuria/) (MedlinePlus, US National Library of Medicine, 2025).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/general-pathology/kidney-stones/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/kidney-stones/