---
title: "What does a low Sodium mean?"
type: biomarker-interpretation
url: "https://www.test-well.com/biomarkers/sodium/low"
biomarker: Sodium
direction: low
reference_range:
  - "age 18+: 135 – 145 mmol/L"
reviewed_at: 2026-09-06
review_status: reviewed
date_published: 2026-09-05
---

# What does a low Sodium mean?

> Low sodium (hyponatremia) is the most common electrolyte abnormality and has many causes: thiazide diuretics, SSRIs and other medications, excess water intake, heart, liver or kidney disease, hypothyroidism, adrenal insufficiency and SIADH (inappropriate antidiuretic hormone from illness, pain, medications or lung and brain conditions). Mild, chronic low sodium is common in older adults; rapid or severe drops cause confusion and seizures.


## When does this result need same-day care?

- Sodium below about 125 mmol/L, or any low value with confusion, vomiting or seizures — emergency care

## What is the normal range for Sodium?

- age 18+: 135 – 145 mmol/L

Can reflect overhydration, certain medications (especially diuretics), or hormonal conditions.

## What are the common causes of low Sodium?

1. Thiazide diuretics, SSRIs, carbamazepine, antipsychotics, NSAIDs
2. Excess water intake relative to salt (endurance events, beer potomania, some diets)
3. Heart failure, cirrhosis, kidney disease
4. SIADH from illness, pain, surgery, or lung/brain disorders
5. Hypothyroidism, adrenal insufficiency
6. Vomiting, diarrhea with water replacement only

## What symptoms go with low Sodium?

- Often none when mild and chronic
- Nausea, headache, fatigue
- Confusion, unsteadiness, falls
- Seizures when severe or rapid

## What do clinicians usually check next?

- Repeat to confirm; review medications and fluid habits
- TSH and morning cortisol
- Urine sodium and osmolality to classify the cause
- Assessment of heart, liver and kidney function

Follow-up tests at TestWell: [TSH (Thyroid Stimulating Hormone)](https://www.test-well.com/tests/tsh) ($26.99), [TSH + Free T4](https://www.test-well.com/tests/tsh-with-free-t4) ($27.99), [Cortisol (AM)](https://www.test-well.com/tests/cortisol-am) ($26.99), [Cortisol](https://www.test-well.com/tests/cortisol-labcorp) ($32.99).

## How do you recheck Sodium?

| Test or panel | Type | Price | Fasting | Results |
| --- | --- | --- | --- | --- |
| [Basic Metabolic Panel](https://www.test-well.com/tests/basic-metabolic-panel) | Test | $20.99 | Yes | 1–3 business days |

Plus one $6 lab processing fee per order; physician authorization included.

## Common questions

### Can drinking too much water lower sodium?

Yes, especially during endurance exercise or with very high fluid intake and low salt. Most hyponatremia, though, is medication- or illness-related.

## Related

- [What does a high Sodium mean?](https://www.test-well.com/biomarkers/sodium/high)
- [Sodium reference ranges](https://www.test-well.com/biomarkers/sodium)
- [Glucose reference range](https://www.test-well.com/biomarkers/glucose)
- [Creatinine reference range](https://www.test-well.com/biomarkers/creatinine)
- [eGFR reference range](https://www.test-well.com/biomarkers/egfr)

## Sources

- [Mayo Clinic Labs](https://www.mayocliniclabs.com/test-catalog/overview/8533)

---

Medically reviewed by Youmna DiStefano, MD (Medical Reviewer, TestWell); last reviewed 2026-09-06. Review policy: https://www.test-well.com/editorial-policy

Canonical page: https://www.test-well.com/biomarkers/sodium/low
Machine-readable catalog: https://www.test-well.com/api/catalog.json · MCP server: https://www.test-well.com/mcp · Overview for agents: https://www.test-well.com/llms.txt

Prices are cash-pay, in USD, and include physician authorization; every order adds one flat $6 lab processing fee. Educational content is not a diagnosis — discuss results with a clinician.