Comparison CMP Updated Apr 17, 2026

Sodium vs Potassium

Sodium (Na) and Potassium (K) are two lab values that can appear on the same metabolic panel and show different aspects of blood composition. They are often reviewed together on a metabolic panel or related lab report because both are measured in mmol/L and help describe how dissolved salts are distributed in blood. Na mainly reflects the amount of sodium in the sample, while K reflects potassium, so the difference between Na and K is in both the element measured and the balance each number represents.

Sodium

Na

Sodium (Na) is a lab value that measures the amount of sodium in blood, usually reported in mmol/L. Sodium on a blood test helps show how concentrated the blood sample is and how water balance is reflected in the result. On a metabolic panel, Na is read alongside other chemistry markers to describe the overall composition of the blood sample.

Adult Male mmol/L
135
145

Potassium

K

Potassium (K) is a blood electrolyte measured on a lab report to show how much K is circulating in the bloodstream. It is commonly included in a metabolic panel and helps describe fluid balance, cell function, and the overall chemical makeup of blood. High or low K values on a blood test are read alongside other markers such as sodium and creatinine.

Adult Male mmol/L
3.5
5

Sodium (Na) and Potassium (K) are two lab values that both appear on the metabolic panel and reflect related aspects of blood composition. Na vs K is a common comparison because each number is reported from the same blood sample but represents a different dissolved mineral. On a lab report, both help show how charged particles are distributed in the fluid portion of blood.

How They Relate

Na measures sodium concentration, while K measures potassium concentration. Both Na and K are listed in mmol/L on a metabolic panel, so the difference between Na and K is the specific mineral being counted. In blood, Na is usually the larger number, while K is usually the smaller number. Because both values come from the same sample, changes in how concentrated the sample is can affect Na and K together. When viewed side by side, Na and K give a quick read on the balance of two major salts in blood.

Key Differences

Aspect Sodium Potassium
What it measures Sodium level Potassium level
Units mmol/L mmol/L
Typical adult range 135–145 3.5–5.0
Reported as Concentration Concentration
Directly reflects Na in fluid K in fluid
Common pairing With chloride With sodium
Difference vs ratio Higher baseline Lower baseline

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Reading Them Together

When Na and K are read together, the pair helps show how the blood sample is balanced. If Na is higher than expected and K is also higher, the pattern often points to a more concentrated sample. If Na is lower while K stays near the usual range, the two numbers are not moving in the same way. When Na and K both sit in their usual ranges, the sample shows a typical balance of these two dissolved salts.

When Both Are Tested

Na and K are often included on the same metabolic panel, especially a basic metabolic panel and a comprehensive metabolic panel. They may also appear together on follow-up lab reports that reuse the same chemistry panel format. In these settings, Na and K provide a fast side-by-side view of two key blood electrolytes without needing separate orders. The same panel usually reports them in mmol/L, which makes the numbers easy to compare on one report.

Frequently Asked Questions

What is the difference between Na and K?
Na measures sodium concentration, while K measures potassium concentration. Both are reported on a blood test in mmol/L, but Na is usually the larger number and K is usually the smaller one. The difference between Na and K is the mineral being measured and the usual range each value falls into.
Which is more important, Na or K?
Na and K are both important, but they describe different parts of blood composition. Na usually changes the overall salt balance of the sample more visibly, while K is smaller in amount and often tracked for a separate reason. On a lab report, neither one replaces the other.
Why are Na and K tested together?
Na and K are tested together because they are part of the same chemistry panel and come from the same blood sample. Reading Na and K side by side makes it easier to compare two major dissolved salts at once. The paired result helps show whether the sample is balanced in a typical way.
Can Na be high while K is low?
Yes, Na and K can move in different directions on the same report. A higher Na with a lower K is a mixed pattern that shows the two minerals are not changing together. That is one reason Na vs K is useful as a comparison, not a single number.
How are Na and K related mathematically?
Na and K do not have a single fixed formula linking them. They are separate concentration values in mmol/L, so any ratio is just a comparison of two numbers on the same report. In many results, Na is several times higher than K.
What units are Na and K measured in?
Na and K are usually measured in mmol/L on a metabolic panel. Some reports may use different unit labels in other regions, but mmol/L is the common format for both values. Using the same units makes Na and K easy to compare.
Are Na and K part of the same panel?
Yes, Na and K are commonly part of the same metabolic panel. They often appear together on both a basic metabolic panel and a comprehensive metabolic panel. That shared placement is why Na and K on a blood test are often discussed together.
What does it mean if Na is 140 and K is 4.0?
Na 140 and K 4.0 are both within typical adult ranges on a metabolic panel. Together, that combination suggests a common side-by-side pattern for these two blood values. It shows Na is near the middle of its usual range while K is in its usual lower range.

Disclaimer

This content is for informational and educational purposes only. It is not intended as medical advice, diagnosis, or treatment recommendation. Reference ranges may vary by laboratory. Always discuss your results with a qualified healthcare professional.