Urine Sodium to Potassium Ratio Calculator
Urine Sodium to Potassium Ratio Calculator
Calculate the urine sodium to potassium ratio, used as a rough marker of mineralocorticoid effect and, on a timed collection, as a dietary surrogate — with descriptive bands rather than guideline thresholds.
Urine Sodium to Potassium Ratio
Na ÷ KUrine sodium 60 mmol/L, urine potassium 30 mmol/L
Formula
- sample type
- a spot sample for the mineralocorticoid question; a 24-hour collection for the dietary question, where a spot sample is a poor substitute
- bands
- descriptive categories used on this page for orientation — they are not guideline thresholds and no society defines them
- diuretics
- loop and thiazide diuretics raise sodium and potassium excretion independently of the underlying physiology and invalidate the ratio entirely
Worked example
Urine sodium 60 mmol/L, urine potassium 30 mmol/L
60 ÷ 30 = 2.00
Between 1 and 3 → typical, and not by itself diagnostic of anything
Descriptive bands used on this page
| Na:K ratio | Description | Consider |
|---|---|---|
| < 1 | Sodium-avid | Mineralocorticoid excess, or simple volume depletion — the ratio cannot distinguish them |
| 1 – 3 | Typical | No diagnostic meaning on its own |
| > 3 | High sodium relative to potassium | High sodium and low potassium intake; also diuretics and recent salt load |
Causes of a low ratio
| Mechanism | Examples |
|---|---|
| Primary mineralocorticoid excess | Primary hyperaldosteronism, Cushing’s syndrome, liquorice ingestion |
| Tubular channel defects | Bartter and Gitelman syndromes |
| Appropriate secondary hyperaldosteronism | Volume depletion, heart failure, cirrhosis, nephrotic syndrome |
Two uses that should not be confused
The urine sodium to potassium ratio is used in two quite different ways, and conflating them is the commonest error. The first is as a marker of mineralocorticoid effect: aldosterone and related steroids drive sodium reabsorption and potassium secretion in the distal nephron, so a strong mineralocorticoid signal pushes urine sodium down and urine potassium up, and the ratio below one. The second is as a dietary surrogate for the sodium-to-potassium intake ratio, an epidemiological measure associated with blood pressure and cardiovascular outcomes.
Those two uses need different samples. The dietary question requires a 24-hour collection, because spot sodium and potassium concentrations swing with the last meal and the last drink; a spot sample is a poor substitute and should not be reported as though it estimated intake. The mineralocorticoid question can be asked of a spot sample, but only alongside the plasma potassium, the acid-base picture and, where relevant, aldosterone and renin.
Be clear about what the bands on this page are. They are descriptive categories, offered for orientation, and no guideline or professional society defines diagnostic cut-offs for this ratio. A value of 0.8 or of 4 is a description of what the kidney is doing on that sample, not a diagnosis, and it should not be recorded as though it were one.
The limitations are substantial. Diuretics invalidate the ratio entirely, because loop and thiazide agents raise sodium and potassium excretion regardless of the underlying physiology. And while the ratio falls in hyperaldosteronism, Cushing’s syndrome, liquorice ingestion and the Bartter and Gitelman syndromes, it falls equally in any state of true volume depletion, where sodium retention is entirely appropriate. The ratio therefore cannot separate appropriate from inappropriate sodium retention on its own, and it is best read as one strand of evidence within a fuller assessment.
Frequently asked questions
How is the urine sodium to potassium ratio calculated?
Divide the urine sodium by the urine potassium, both in mmol/L and from the same sample. On a spot sample the ratio reflects the moment; the dietary version requires a 24-hour collection.
Are the bands on this page diagnostic thresholds?
No. They are descriptive categories used here for orientation. No guideline or professional society defines diagnostic cut-offs for the urine sodium to potassium ratio, and a value should not be recorded as a diagnosis.
What does a ratio below one mean?
Sodium is being retained relative to potassium, which is the pattern of a strong mineralocorticoid effect. The same pattern occurs in ordinary volume depletion, so the ratio cannot separate appropriate from inappropriate sodium retention.
Can the ratio be used in a patient on diuretics?
No. Loop and thiazide diuretics raise both sodium and potassium excretion independently of the underlying physiology, which invalidates the ratio entirely.
Can a spot sample estimate dietary sodium to potassium intake?
Poorly. Spot concentrations vary with the last meal and the last drink, so a 24-hour collection is required if the question is about intake.
Related calculators
References
- Mente A, O’Donnell MJ, Rangarajan S, et al. Association of urinary sodium and potassium excretion with blood pressure. N Engl J Med. 2014;371(7):601–611.
- Rose BD, Post TW. Clinical Physiology of Acid-Base and Electrolyte Disorders. 5th ed. McGraw-Hill; 2001.