Sodium in Cats: Normal Range, High and Low Levels (2026)

Q: What is the normal sodium level for cats?

Normal sodium (Na+) in cats is approximately 145–158 mEq/L — slightly higher than the dog reference range. Sodium is the primary extracellular electrolyte and is tightly regulated by the kidneys under the influence of aldosterone and antidiuretic hormone (ADH). It determines plasma osmolality and governs water distribution between body fluid compartments.

Q: What causes low sodium in cats?

Low sodium (hyponatremia) in cats is most commonly caused by: chronic kidney disease with concurrent heart disease or hypertension-driven fluid retention; congestive heart failure; pleural or abdominal effusions — when fluid builds up in body cavities, it reflects dilutional fluid retention; liver failure; and, less commonly, Addison's disease (rare in cats). The mechanism in most of these is dilutional — sodium concentration drops because excess water is retained.

Q: What causes high sodium in cats?

High sodium (hypernatremia) in cats most commonly means dehydration — the cat has lost more water than sodium. Additional causes include diabetes insipidus (central or nephrogenic — the kidneys cannot concentrate urine, causing continuous dilute urine production and progressive water loss), and hyperosmolar diabetic crisis. Dehydration is by far the most common cause in everyday clinical practice.

Q: Can CKD cause low sodium in cats?

CKD alone rarely causes hyponatremia directly. However, cats with advanced CKD often have concurrent conditions — systemic hypertension managed with amlodipine (which doesn't affect sodium directly), concurrent heart disease, or antidiuretic hormone dysregulation — that can contribute to sodium abnormalities. When a CKD cat has low sodium, it often points to a concurrent problem like CHF, effusion, or the sodium loss from repeat fluid therapy with inadequate electrolyte balance.

Q: Does high sodium mean my cat is just thirsty?

Mild hypernatremia can reflect simple dehydration — if your cat has been eating less, vomiting, or had diarrhea. However, persistent or severe hypernatremia despite water availability suggests a water balance disorder such as diabetes insipidus. In DI, cats drink large volumes but cannot retain water due to ADH deficiency (central DI) or renal tubule resistance to ADH (nephrogenic DI). The diagnostic test is measuring urine specific gravity: a very dilute urine despite high plasma sodium confirms a concentrating defect.

Sodium is the body's primary fluid-control electrolyte. Its concentration tells you less about how much sodium there is and more about how water is being handled — too little water relative to sodium, or too much. In cats, sodium abnormalities most often reflect underlying conditions like CKD complications, cardiac disease, or dehydration rather than sodium intake per se.

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Normal Sodium Range in Cats

Normal sodium (Na+) in cats is 145–158 mEq/L — slightly higher than the dog reference range. The body maintains this concentration through the interplay of aldosterone (promotes sodium retention at the kidney) and ADH/vasopressin (promotes water retention). When sodium is outside this range, one of these systems — or the conditions they're responding to — has gone wrong.

<135 mEq/L

Severe hyponatremia — neurological risk, controlled correction required

135–145 mEq/L

Mild hyponatremia — investigate cause

145–158 mEq/L

Normal

158–168 mEq/L

Mild hypernatremia — dehydration most likely

>168 mEq/L

Severe hypernatremia — urgent controlled rehydration

Na+ Level (mEq/L)	Interpretation
<135	Severe hyponatremia — neurological risk, controlled correction required
135–145	Mild hyponatremia — investigate underlying cause
145–158	Normal
158–168	Mild hypernatremia — dehydration most likely, rehydrate
>168	Severe hypernatremia — urgent controlled rehydration

Low Sodium (Hyponatremia) in Cats

Low sodium in cats is almost always dilutional — meaning there's excess water relative to sodium, rather than sodium deficiency per se. The kidney is either retaining too much water or fluid is accumulating in body cavities.

Congestive Heart Failure (CHF)

Cats with hypertrophic cardiomyopathy (HCM) or other cardiac diseases can develop CHF, and fluid retention is a key feature. The renin-angiotensin-aldosterone system activates to retain fluid, but water is retained in excess of sodium, diluting plasma Na+. Concurrent pleural effusion — fluid in the chest cavity — is extremely common in cats with CHF and amplifies this pattern. A cat with hyponatremia alongside respiratory difficulty and a pleural effusion should be evaluated for cardiac disease urgently.

Pleural and Abdominal Effusions

Any condition causing effusion — FIP, cancer, hepatic disease, cardiac failure — involves third-spacing of fluid. This activates compensatory hormonal mechanisms that retain sodium and water in the bloodstream, but the net effect on measured sodium concentration can be dilutional. The hyponatremia here is a marker of the overall fluid-retaining state, not a primary electrolyte disorder.

Liver Disease

Portal hypertension from hepatic lipidosis, cholangiohepatitis, or cirrhosis causes fluid to shift into the abdominal cavity (ascites) and activates the same fluid-retaining cascade as heart failure. Sodium dilution follows. A cat with ascites, low albumin, and low sodium has a hepatic disease pattern worth investigating with ultrasound and liver biopsy.

Hypoadrenocorticism (Rare in Cats)

Addison's disease is uncommon in cats compared to dogs, but when it occurs, the same aldosterone-failure pattern produces low Na+ and high K+. Cats with Addison's may be less dramatically ill than dogs and are sometimes diagnosed late. The electrolyte pattern mirrors the dog pattern: hyponatremia with concurrent hyperkalemia and Na:K ratio below 27.

High Sodium (Hypernatremia) in Cats

Dehydration

The most common reason a cat's sodium is elevated is simple dehydration. Cats are notoriously poor water drinkers — a dry food diet provides minimal moisture, and sick or stressed cats drink even less. Dehydration concentrates all dissolved electrolytes including sodium. This is typically mild (Na+ 160–170 mEq/L) and corrects with rehydration and addressing the underlying illness or diet.

Diabetes Insipidus

Diabetes insipidus (DI) is uncommon in cats but recognized. In central DI, the hypothalamus or pituitary fails to produce or release ADH. In nephrogenic DI, the kidneys are resistant to ADH. Both result in massive dilute urine production that cannot be stopped. Cats with DI drink enormous volumes but still develop hypernatremia and dehydration because output exceeds intake. The diagnostic clue is a low urine specific gravity (often below 1.006) despite elevated plasma sodium — the kidney is making dilute urine when it should be concentrating.

Hyperosmolar Diabetic Crisis

Severe hyperglycemia causes osmotic diuresis — glucose pulls water into the urine. Cats can develop a hyperosmolar state with very high glucose and elevated sodium as severe dehydration follows. This is an endocrine emergency requiring careful insulin and fluid management.

Cats vs. Dogs: Key Sodium Differences

Cats have a higher normal Na+ range (145–158) than dogs (140–155).
Addison's disease is far less common in cats — don't lead with that diagnosis as you would in dogs.
Pleural effusion from HCM is a very feline reason for dilutional hyponatremia.
Chronic dehydration from dry food diets makes mild hypernatremia common in cats.

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Frequently Asked Questions

What is the normal sodium level for cats?

Normal sodium in cats is approximately 145–158 mEq/L — slightly higher than the dog range. It's tightly regulated by aldosterone and ADH and governs water distribution between body fluid compartments.

What causes low sodium in cats?

Hyponatremia in cats most commonly comes from: congestive heart failure, pleural or abdominal effusions (dilutional fluid retention), liver failure, and occasionally CKD with concurrent disease. The mechanism in most cases is dilutional — excess water retention drops the concentration.

What causes high sodium in cats?

Hypernatremia in cats most commonly means dehydration. Diabetes insipidus (central or nephrogenic) causes continuous dilute urine production and persistent water loss despite drinking. Hyperosmolar diabetic crisis is another cause.

Can CKD cause low sodium in cats?

CKD alone rarely causes hyponatremia directly. When a CKD cat has low sodium, it typically points to a concurrent condition — CHF, effusion, or the dilutional effects of fluid therapy. The sodium abnormality is usually a signal of the overall clinical picture, not CKD itself.

Does high sodium mean my cat is just thirsty?

Mild elevation can reflect simple dehydration. Persistent or severe hypernatremia despite water access suggests diabetes insipidus — the diagnostic clue is a very dilute urine (low specific gravity) despite high plasma sodium, confirming a concentrating defect.

Sodium in Cats: What High and Low Na+ Levels Mean