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# Cystinuria

In cystinuria the [kidney](https://durgical.com/en/anatomy/kidney/) does not reabsorb cystine, which is poorly soluble and forms repeated urinary stones from a young age.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Kidneys](https://durgical.com/en/anatomy/kidney/)
- [Renal pelvis](https://durgical.com/en/anatomy/renal-pelvis/)
- [Ureters](https://durgical.com/en/anatomy/ureter/)
- [Urinary bladder](https://durgical.com/en/anatomy/urinary-bladder/)
- [Jejunum](https://durgical.com/en/anatomy/jejunum/)

## In biochemistry

- [Membrane structure](https://durgical.com/en/biochemistry/topics/membrane-structure/)
- [Membrane transport](https://durgical.com/en/biochemistry/topics/membrane-transport/)
- [Urinalysis](https://durgical.com/en/biochemistry/topics/urinalysis/)
- [Amino acids: structure, charge and pKa](https://durgical.com/en/biochemistry/topics/amino-acids-structure-charge-and-pka/)
- [Protein structure and folding](https://durgical.com/en/biochemistry/topics/protein-structure-and-folding/)

## In physiology

- [Protein digestion and absorption](https://durgical.com/en/physiology/protein-digestion-and-absorption/)
- [Proximal tubule transport](https://durgical.com/en/physiology/proximal-tubule-transport/)

## What it is

An inherited disorder of amino acid transport in the renal proximal tubule and the gut. Cystine, ornithine, lysine and arginine are lost in urine.

## Who gets it

It affects about 1 in 10,000 people and causes a small share of kidney stones, but a larger share in children.

## Causes

- Variants in SLC3A1 or SLC7A9, the two subunits of the dibasic amino acid and cystine transporter

## Risk factors

- Family history
- Low water intake
- Acidic urine
- Diet high in sodium and animal protein

## Pathophysiology

The brush-border transporter does not recover cystine or the dibasic amino acids (ornithine, lysine, arginine; mnemonic COLA). Cystine is poorly soluble in acidic urine and crystallises as hexagons that form stones. The other amino acids are lost without clinical effect.

## Symptoms and signs

- Recurrent renal colic
- Haematuria
- Urinary infections
- Stones from childhood or youth

## Red flags

- Colic with fever (obstructive infection)
- Falling kidney function
- Anuria from bilateral obstruction

## Diagnosis

**Clinical**
Recurrent stones in a young person or with a family history.

**Tests**
Hexagonal crystals in urine sediment; positive cyanide–nitroprusside test; high 24-hour urinary cystine; stone analysis; genetic testing.

**Imaging**
Non-contrast CT or ultrasound to locate the stones; they are faintly radio-opaque on plain X-ray.

## Treatment

**Lifestyle**
Plenty of water day and night, less salt and less animal protein

**Medical**
Alkalinising urine with potassium citrate so cystine dissolves better

**Medical**
Thiol drugs (tiopronin, D-penicillamine) that form a soluble compound with cysteine

**Procedure**
Ureteroscopy or percutaneous nephrolithotomy for stones that do not pass

## Complications

- Urinary obstruction
- Pyelonephritis
- Chronic kidney disease from stones and repeated procedures

## Prognosis

A lifelong disease with frequent recurrences; well-kept hydration and alkalinisation reduce stones.

## Test yourself

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

## Which amino acids are lost in urine in cystinuria?

Cystine, ornithine, lysine and arginine (COLA), from failure of one proximal tubule transporter.

## What shape are cystine crystals?

Flat hexagons in urine sediment.

## Why is urine alkalinised in cystinuria?

Cystine is much more soluble in alkaline urine, so it crystallises less.

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## Related conditions

- [Hartnup disease](https://durgical.com/en/conditions/hartnup-disease/)
- [Kidney stones (urolithiasis)](https://durgical.com/en/conditions/kidney-stones/)
- [Acute pyelonephritis](https://durgical.com/en/conditions/acute-pyelonephritis/)
- [Chronic kidney disease](https://durgical.com/en/conditions/chronic-kidney-disease/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Cystinuria: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/cystinuria/) (MedlinePlus, US National Library of Medicine, 2026); [SLC3A1 gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/slc3a1/) (MedlinePlus, US National Library of Medicine, 2026); [Amino acid transport across the plasma membrane](https://reactome.org/PathwayBrowser/#/R-HSA-352230) (Reactome, 2026).

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Source: https://durgical.com/en/conditions/cystinuria/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/cystinuria/