Serum/plasma sodium concentration (qualitative probe)

Doctors order a sodium blood test to check how well your body is balancing water and electrolytes. Sodium helps control blood pressure, nerve signals, and muscle function, so this test is often part of a basic metabolic panel. It may be done if you have symptoms such as dehydration, confusion, weakness, or swelling, or if you take medicines like diuretics that affect fluid balance.

Your healthcare provider may order this test to check for conditions like dehydration, high blood pressure, kidney problems, or electrolyte imbalances. It can also help diagnose or monitor certain medical conditions, such as heart failure or syndrome of inappropriate antidiuretic hormone (SIADH).

A normal result means your sodium level falls within the typical range of 135 to 145 mEq/L. A level below this range, called hyponatremia, may mean your body is holding too much water, while a level above it, called hypernatremia, often points to dehydration. Your doctor will interpret your result alongside your symptoms, medical history, and other test values.

Results are qualitative (not numerical), so they indicate whether sodium levels are too high (hypernatremia) or too low (hyponatremia) compared to what’s typical for healthy blood. Your provider will interpret the result in the context of your symptoms and overall health.

Abnormal sodium levels can be linked to conditions such as kidney disease, heart failure, liver cirrhosis, adrenal gland disorders like Addison's disease, diabetes insipidus, and severe vomiting or diarrhea. Certain medicines, including diuretics, antidepressants, and some pain relievers, can also lower sodium, while not drinking enough water can raise it.

High sodium levels may be linked to conditions like severe dehydration, kidney disease, or excessive use of salt. Low sodium levels might suggest conditions like heart failure, liver disease, or excessive water intake.

This test requires a simple blood draw, usually from a vein in your arm. A healthcare professional will clean the site, wrap a band around your upper arm, and collect a small sample into a tube. The procedure takes only a few minutes, and you may feel a brief pinch. You can usually eat and drink beforehand unless your doctor gives other instructions, and you can return to normal activities right away.

A small blood sample is drawn from a vein, usually in your arm. The process is quick and typically painless. You may feel a slight pinch, but it usually doesn’t cause discomfort afterward.