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# Essential fructosuria

Essential fructosuria is a benign inherited trait: fructose is not processed and leaves in the urine, causing no symptoms.

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/)
- [Urinary bladder](https://durgical.com/en/anatomy/urinary-bladder/)
- [Liver](https://durgical.com/en/anatomy/liver/)

## In biochemistry

- [Fructose metabolism: Step 3 · Fructokinase (ketohexokinase)](https://durgical.com/en/biochemistry/pathways/fructose-metabolism/#paso-3)
- [Fructose](https://durgical.com/en/biochemistry/molecules/fructose/)

## What it is

Lack of fructokinase (ketohexokinase, KHK gene). Dietary fructose stays in the blood and is cleared by the [kidney](https://durgical.com/en/anatomy/kidney/).

## Who gets it

Rare; its true frequency is unknown because it causes no symptoms and many cases go unnoticed.

## Causes

- Autosomal recessive inheritance: KHK gene variants

## Risk factors

- Carrier parents

## Pathophysiology

Without fructokinase, fructose is not phosphorylated in the [liver](https://durgical.com/en/anatomy/liver/). Part of it is slowly phosphorylated by muscle and adipose hexokinase to fructose 6-phosphate; the rest leaves in the urine. Since no fructose 1-phosphate forms, phosphate is not trapped and ATP does not fall: hence no damage.

## Symptoms and signs

- It causes no symptoms
- It is found through a positive urine reducing-sugar test

## Red flags

- None of its own; if symptoms follow fructose intake, consider hereditary fructose intolerance

## Diagnosis

**Clinical**
Incidental finding of sugar in the urine in a healthy person with normal blood glucose.

**Tests**
Positive reducing-sugar test with a negative glucose strip; identification of fructose in urine by chromatography; KHK gene testing if needed.

**Imaging**
No imaging is needed.

## Treatment

**Follow-up**
No treatment needed; explaining the finding avoids a mistaken diagnosis of diabetes

## Complications

- None known; the risk is a wrong diagnosis of diabetes

## Prognosis

Excellent: normal life.

## Test yourself

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

## Which enzyme is missing in essential fructosuria?

Fructokinase (ketohexokinase, KHK).

## Why is essential fructosuria benign while hereditary fructose intolerance is not?

Without fructokinase no fructose 1-phosphate forms, the toxic molecule that traps phosphate.

## Which urine test pattern suggests fructosuria?

Positive reducing sugars with a negative glucose strip.

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## Related conditions

- [Hereditary fructose intolerance](https://durgical.com/en/conditions/hereditary-fructose-intolerance/)
- [Type 1 diabetes mellitus](https://durgical.com/en/conditions/type-1-diabetes-mellitus/)
- [Type 2 diabetes mellitus](https://durgical.com/en/conditions/type-2-diabetes-mellitus/)

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

Sources: [KHK: Ketohexokinase (human)](https://www.uniprot.org/uniprotkb/P50053/entry) (UniProt, 2026); [Fructose metabolism](https://reactome.org/PathwayBrowser/#/R-HSA-5652084) (Reactome, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Representative model, for educational purposes only.

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