Sodium blood test (Na)
A sodium test measures blood sodium to assess hydration and electrolyte balance, with convenient Quest lab ordering and PocketMD guidance at Vitals Vault.
This panel bundles multiple biomarker tests in one order—your report explains how results fit together.
Sodium is one of the main electrolytes in your blood. It helps control how much water is inside and outside your cells, and it supports nerve signaling and muscle function.
A sodium blood test is usually ordered as part of a broader chemistry panel, so it often shows up on your results even if you did not specifically request it. When it is out of range, the “why” is often more important than the number itself.
Because sodium is tightly regulated by your kidneys and hormones, an abnormal result can point to dehydration or overhydration, medication effects, or a medical condition that changes how your body handles water and salt.
Do I need a Sodium test?
You may want a sodium test if you have symptoms that could reflect an electrolyte or fluid-balance problem, such as unusual fatigue, headaches, nausea, confusion, muscle cramps, weakness, or new swelling. More severe sodium shifts can contribute to dizziness, fainting, or changes in alertness, which should be evaluated urgently.
Testing is also common if you are managing a condition or situation that can shift sodium, including vomiting or diarrhea, heavy sweating, very high water intake, kidney disease, heart failure, liver disease, uncontrolled diabetes, or recent hospitalization. Your clinician may also monitor sodium if you take medications that affect water and salt handling, such as diuretics (“water pills”), certain antidepressants, anti-seizure medications, or desmopressin.
If you are comparing options, sodium is most useful when it is interpreted alongside related markers (especially potassium, chloride, bicarbonate/CO2, glucose, and kidney function). Your result can support clinician-directed care, but it is not a stand-alone diagnosis.
Sodium is measured on automated chemistry analyzers in CLIA-certified laboratories; results should be interpreted with your symptoms, medications, and companion labs rather than used for self-diagnosis.
Lab testing
Order sodium as part of a BMP or CMP so you can interpret it with the electrolytes and kidney markers that matter.
Schedule online, results typically within about a week
Clear reporting and optional clinician context
HSA/FSA eligible where applicable
Get this test with Vitals Vault
If you want a clear, convenient way to check sodium, Vitals Vault lets you order lab testing directly and complete your blood draw at a Quest location. Sodium is typically included in common panels (like a BMP or CMP), which can be a better value than ordering it in isolation when you also want kidney function and other electrolytes.
After your results are in, you can use PocketMD to ask targeted questions such as what a mildly low sodium might mean for your specific medications, whether your pattern suggests dehydration versus water retention, and what follow-up tests are commonly paired with sodium.
If your sodium is meaningfully abnormal or you feel unwell, the next step is usually not “more sodium” or “less sodium” on your own. It is clarifying the cause and confirming the trend with repeat testing and related labs, ideally with clinician guidance.
- Order online and draw at a Quest location
- Results you can track over time in one place
- PocketMD helps you prepare smarter follow-up questions
Key benefits of Sodium testing
- Helps assess hydration status and overall fluid balance when symptoms are nonspecific.
- Flags hyponatremia or hypernatremia early, which can affect brain and muscle function if severe.
- Adds context to dizziness, weakness, confusion, cramps, nausea, or unexplained fatigue.
- Supports medication monitoring, especially when you use diuretics or other drugs that shift water and salt handling.
- Pairs with kidney markers (BUN, creatinine, eGFR) to clarify whether the kidneys are contributing to the imbalance.
- Improves interpretation of acid–base and electrolyte patterns when reviewed with chloride and bicarbonate (CO2).
- Makes it easier to trend changes over time and decide when a repeat test is warranted.
What is Sodium?
Sodium (Na) is a mineral and electrolyte that circulates in your blood and body fluids. It is the main positively charged electrolyte outside your cells, so it strongly influences where water sits in your body.
Your body regulates sodium through a balance of thirst, kidney function, and hormones such as antidiuretic hormone (ADH/vasopressin), aldosterone, and natriuretic peptides. In many real-world cases, an “abnormal sodium” result is actually telling you about a water-balance problem (too much or too little body water) rather than a simple dietary salt issue.
Most labs report sodium as a concentration in blood (often called serum sodium). The number can shift quickly with acute illness, changes in fluid intake, IV fluids, or medication changes, so timing and context matter.
Sodium vs. salt intake
Dietary salt (sodium chloride) influences long-term health, especially blood pressure, but a single sodium blood level usually does not reflect how salty your diet is. Your kidneys and hormones keep blood sodium in a narrow range by adjusting water and sodium excretion.
Why sodium is often ordered with other labs
Sodium is most informative when you also see potassium, chloride, bicarbonate (CO2), glucose, and kidney function. Those results help distinguish dehydration from water retention, medication effects, kidney-related causes, and acid–base patterns.
What do my Sodium results mean?
Low sodium (hyponatremia)
Low sodium often means your body has relatively too much water compared with sodium, although true sodium loss can also occur. Common contributors include certain medications (especially diuretics and some antidepressants), vomiting/diarrhea with fluid replacement, hormonal signaling that causes water retention (such as SIADH), and advanced heart, liver, or kidney disease. Mild low sodium may cause few symptoms, but larger drops can lead to headache, confusion, unsteadiness, or worsening fatigue. Because rapid correction can be dangerous, persistent or symptomatic hyponatremia should be managed with clinician guidance rather than self-treatment.
In-range sodium (typical balance)
An in-range sodium result usually suggests your kidneys and hormones are keeping water and electrolytes in balance at the time of testing. It does not rule out dehydration, overhydration, or illness entirely, but it makes a major sodium disturbance less likely. If you still have symptoms, your clinician may look at trends over time and at companion markers like potassium, chloride, bicarbonate (CO2), glucose, and kidney function to find a better explanation.
High sodium (hypernatremia)
High sodium most often reflects a relative water deficit, meaning you have lost more water than sodium or you are not taking in enough fluids. This can happen with dehydration from fever, sweating, diarrhea, or inadequate access to water, and it can also occur with conditions that increase water loss (such as uncontrolled high blood sugar with frequent urination). Some cases relate to impaired thirst or hormonal regulation (for example, diabetes insipidus). Because significant hypernatremia can affect brain function, a high result—especially with symptoms like confusion or marked weakness—deserves prompt medical evaluation.
Factors that influence sodium results
Your sodium level can shift with recent fluid intake, IV fluids, vomiting/diarrhea, heavy exercise and sweating, and acute illness. Medications are a frequent driver, including diuretics, SSRIs/SNRIs, carbamazepine/oxcarbazepine, and desmopressin, among others. High blood glucose can lower measured sodium concentration (a dilution effect), so sodium is often interpreted alongside glucose. Lab handling issues are uncommon but possible, and repeating the test can help confirm an unexpected result.
What’s included
- Sodium
Frequently Asked Questions
What is a normal sodium level?
Most labs use a reference range around 135–145 mmol/L (mEq/L), but the exact range can vary by lab and method. Your best comparison is the range printed next to your result, plus your prior results if you have them.
Do I need to fast for a sodium blood test?
Fasting is not usually required for sodium by itself. However, sodium is commonly ordered in a BMP or CMP that includes glucose, and some clinicians prefer fasting for the most consistent glucose interpretation. Follow the collection instructions provided with your order.
Can drinking a lot of water lower sodium?
It can, especially if you drink large amounts quickly or if your body is already retaining water due to hormones, medications, or illness. Mild changes may be temporary, but persistent low sodium should be evaluated to identify the underlying cause.
Is low sodium caused by not eating enough salt?
Usually not. Blood sodium is regulated mainly by water balance and kidney/hormone control, so low sodium more often reflects too much body water relative to sodium, medication effects, or illness rather than low dietary salt intake.
What symptoms can high or low sodium cause?
Mild abnormalities may cause no symptoms. Larger shifts can cause headache, nausea, cramps, weakness, irritability, confusion, or trouble concentrating, and severe abnormalities can affect alertness and balance. If you have significant symptoms, seek medical care promptly.
How often should sodium be rechecked if it is abnormal?
That depends on how abnormal it is, whether you have symptoms, and what is suspected to be causing it. Mild, stable abnormalities may be rechecked in days to weeks, while more significant changes or medication adjustments may require faster follow-up. Your clinician can set the safest interval for your situation.
What other tests help interpret sodium?
Common companions include potassium, chloride, bicarbonate (CO2), glucose, BUN, creatinine, and eGFR. In specific situations, clinicians may add serum and urine osmolality, urine sodium, thyroid testing, or cortisol testing to clarify why sodium is off.