[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Physiology](https://durgical.com/en/physiology/) › [Renal, fluids and acid–base](https://durgical.com/en/physiology/#s-renal) › Glucose transport maximum and renal threshold

[Physiology](https://durgical.com/en/physiology/) · [Renal, fluids and acid–base](https://durgical.com/en/physiology/#s-renal)

# Glucose transport maximum and renal threshold

- Measurement
- Exam priority: medium

The kidney reclaims all filtered glucose up to a limit; when blood glucose goes past it, glucose spills into the urine.

Updated 2026-11-01

Also called: Glucose Tm, Glucosuria, Renal threshold for glucose

**See it in 3D:** [Kidneys](https://durgical.com/en/anatomy/kidney/)

## Key points

- Filtered load = GFR × plasma glucose: at 125 mL/min and 100 mg/dL, ≈125 mg/min, all reabsorbed.
- Renal threshold ≈180–200 mg/dL plasma glucose in adults; whole-kidney Tm ≈300–375 mg/min.
- Glucosuria starts before Tm because of nephron heterogeneity and transporter affinity (splay).
- Above Tm, excretion rises linearly with plasma glucose.
- Unreabsorbed glucose holds water in the tubule: osmotic diuresis, polyuria and thirst in diabetes.
- Glucosuria with normal blood glucose = low threshold: pregnancy, SGLT2 inhibitors, familial renal glucosuria, Fanconi syndrome.

## What it is

Glucose is freely filtered and the proximal tubule reclaims it with sodium-coupled transporters that can saturate. As long as the filtered load is below their capacity, there is no glucose in the urine. The renal threshold is the plasma glucose at which glucosuria begins; the transport maximum (Tm) is the whole kidney’s maximal reabsorption. Between the two lies a curved zone (“splay”) because not all nephrons saturate at once.

### The nephron: segments, transporters and diuretics

**Na⁺ reabsorbed** ≈ 65–70% **Water reabsorbed** ≈ 65–70%

#### Proximal tubule

- **What it does:** Reabsorbs ≈ 65–70% of filtered Na⁺ and water (isosmotically), nearly all glucose and amino acids, ≈ 80% of HCO₃⁻ and most K⁺ and phosphate. Secretes organic acids and bases (many drugs) and makes NH₄⁺ from glutamine.
- **Transporters:** NHE3 (Na⁺/H⁺) with carbonic anhydrase; SGLT2 (early segment, ≈ 90% of glucose) and SGLT1; NaPi-2a (phosphate); basolateral Na⁺/K⁺-ATPase.
- **Hormones:** Ang II stimulates NHE3 (more Na⁺ and HCO₃⁻: contraction alkalosis); PTH inhibits NaPi-2a (phosphaturia) and activates 1α-hydroxylase (active vitamin D).
- **Drugs:** Carbonic anhydrase inhibitors (1), SGLT2 inhibitors (2) and osmotic diuretics (3, with the thin descending limb).
- **Disorders:** Fanconi syndrome (loses glucose, amino acids, phosphate and HCO₃⁻); type 2 (proximal) renal tubular acidosis; familial renal glucosuria (SGLT2).

- Glomerulus and arterioles
- Proximal tubule
- Thin descending limb
- Thin ascending limb
- Thick ascending limb
- Distal convoluted tubule
- Collecting tubule and duct
- Juxtaglomerular apparatus (macula densa)
- Cortex
- Medulla
- Interstitial osmolality (≈ 300 → 1200 mOsm/kg)

Illustrative schematic drawn by Durgical (a long-loop juxtamedullary nephron); proportions and percentages are approximate and not for clinical decisions.

## Equations

**Filtered load**FL = GFR × Pglu

**P glu**
plasma glucose (mg/mL)

**Excretion**E = FL − R

**R**
reabsorption (at most, the Tm)

If FL ≤ Tm, E ≈ 0 (apart from the splay zone).

## Approximate figures (adult)

| Parameter | Value | Note |
| --- | --- | --- |
| Fasting plasma glucose | ≈70–100 mg/dL | |
| Renal threshold for glucose | ≈180–200 mg/dL | lower in pregnancy and with SGLT2 inhibitors |
| Transport maximum (Tm) | ≈300–375 mg/min | varies between sources and people |
| Reabsorption by SGLT2 / SGLT1 | ≈90 % / ≈10 % | early and late proximal tubule |

Approximate values for a healthy adult at rest; each laboratory sets its own ranges.

## Clinical notes

- In poorly controlled diabetes, glucosuria causes osmotic diuresis: polyuria, polydipsia, sodium and potassium loss, and a risk of dehydration.
- In pregnancy GFR rises: filtered load increases and glucosuria can occur with normal blood glucose.
- A urine dipstick detects glucose only once plasma glucose has passed the threshold: it is not a test for diagnosing diabetes.

## Memory aid

“The glucose bus has a fixed number of seats”: up to ≈180 mg/dL everyone rides back to the blood; whoever doesn’t fit leaves in the urine.

## Test yourself

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

## With a GFR of 120 mL/min, plasma glucose of 400 mg/dL and a Tm of 375 mg/min, how much glucose is excreted?

Filtered load = 1.2 dL/min × 400 mg/dL = 480 mg/min. 375 is reabsorbed; ≈105 mg/min is excreted.

## Why does glucose appear in urine before the whole kidney reaches its Tm?

Nephrons differ in reabsorptive capacity and in load: some saturate before others. That heterogeneity produces the splay.

## Why can heavy glucosuria cause hypernatraemia and dehydration?

Glucose left in the lumen prevents water reabsorption (osmotic diuresis): water is lost in greater proportion than sodium, and extracellular volume falls.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/physiology/glucose-transport-maximum-and-renal-threshold/)

## See it in 3D

The structures of Durgical's 3D anatomy where it happens.

- [Kidneys](https://durgical.com/en/anatomy/kidney/)

## Related topics

- [Proximal tubule transport](https://durgical.com/en/physiology/proximal-tubule-transport/)
- [Urine dilution, free water and osmotic diuresis](https://durgical.com/en/physiology/urine-dilution-free-water-and-osmotic-diuresis/)
- [Physiology of diabetes and ketoacidosis](https://durgical.com/en/physiology/physiology-of-diabetes-and-ketoacidosis/)
- [Renal clearance](https://durgical.com/en/physiology/renal-clearance/)

## Related conditions

- [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/)
- [Diabetic ketoacidosis](https://durgical.com/en/conditions/diabetic-ketoacidosis/)

## In Biochemistry

- [Glucose](https://durgical.com/en/biochemistry/molecules/glucose/)
- [Membrane transport](https://durgical.com/en/biochemistry/topics/membrane-transport/)

[← All of physiology](https://durgical.com/en/physiology/)

Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: [25.6 Tubular Reabsorption](https://openstax.org/books/anatomy-and-physiology-2e/pages/25-6-tubular-reabsorption) (OpenStax (Rice University), 2022); [Type 2 Diabetes](https://www.ncbi.nlm.nih.gov/books/NBK513253/) (StatPearls (NCBI Bookshelf), 2024); [Type 1 Diabetes](https://www.ncbi.nlm.nih.gov/books/NBK507713/) (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 28). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

## **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/physiology/glucose-transport-maximum-and-renal-threshold/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/glucose-transport-maximum-and-renal-threshold/