Biomarkers

Low anion gap: What it means and when to follow up

Understand a low anion gap result, common explanations, and how metabolic panel results guide follow-up.

Published

September 29, 2026

Read time

5 min read

Medically reviewed by

Rhonda Collins, FNP-C

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A low anion gap is a clue from your blood test, not a diagnosis. The number is calculated from other results on a metabolic panel, so the first steps are to check your laboratory’s reference range and confirm an unexpected result. A measurement issue or low albumin often explains it. If the result persists, your other test results and health history help determine what to check next. The Cleveland Clinic Journal of Medicine review recommends confirming the result before investigating less common causes.

What is the anion gap?

The anion gap is a calculation: sodium − (chloride + bicarbonate). These are measured electrolytes, while the gap itself is not a substance measured directly. Bicarbonate may appear as carbon dioxide or CO2 on your report. The calculation helps clinicians interpret the balance of charged particles that a routine panel does not individually measure. It is not a direct measurement of blood pH, and it is different from the albumin/globulin, or A/G, ratio. The clinical review describes the calculation; MedlinePlus explains how panel results are used.

Both a basic metabolic panel (BMP) and a comprehensive metabolic panel (CMP) measure the electrolytes used in this calculation. A CMP also measures albumin, which can help put a low gap in context.

Some laboratories include a calculated anion gap on their reports. Mito reports the component values, but does not report an anion-gap value.

See our BMP versus CMP comparison, the Basic Metabolic Panel (BMP), or the Comprehensive Metabolic Panel (CMP) for the panel that fits the information you need. The MedlinePlus BMP and CMP descriptions list their included measurements.

What counts as a low anion gap?

Use the reference range printed by the laboratory that tested your sample. Methods and calculations differ. For example, a Cleveland Clinic Journal of Medicine review describes a method-dependent reference range of 3–9 mEq/L and defines a low result in that setting as 3 mEq/L or less. Those figures are examples, not a universal cutoff to apply to every report. MedlinePlus also notes that normal results vary by laboratory.

What causes a low anion gap?

Measurement error is the most common explanation for a low anion gap. Because the gap is calculated from three measured values, an error in any one can change it. The clinical review recommends repeating serum electrolyte testing when the result is unexpected.

Low albumin is an important explanation for a genuinely low result. Albumin is a negatively charged blood protein. When albumin is lower, the calculated gap often falls too. Low albumin itself can accompany health conditions, including kidney or liver disease, so it is a finding to interpret rather than a reason to dismiss the result. A clinician may account for albumin when interpreting the gap. Clinical review; MedlinePlus.

Less common explanations include medicines and unusual blood proteins. Lithium can lower the gap. A high concentration of certain positively charged proteins can do the same. One example is a monoclonal protein, sometimes called a paraprotein, made by one group of plasma cells. This pattern can occur in monoclonal gammopathies, including multiple myeloma. The gap alone cannot identify which, if any, condition is present. Clinical review; study of monoclonal gammopathies.

Does a low anion gap cause symptoms, and what happens next?

The calculated anion gap does not itself cause symptoms. Symptoms, when present, come from an underlying condition and vary with that condition. A clinician can review an unexpected result against the laboratory range, repeat the electrolytes if needed, and consider albumin, medicines, other panel results, symptoms, and whether the low value persists. An isolated low result cannot tell you which explanation applies. MedlinePlus; clinical review.

If your result shows low CO2 with a high anion gap, see our low CO2 explainer.

Frequently asked questions

Should I be worried if my anion gap is low?

An isolated low result does not establish a disease. Check the range on your report and whether repeat testing confirms it. A persistent result, other abnormal values, or symptoms gives your clinician more reason to investigate. Clinical review.

What cancers show a low anion gap?

Multiple myeloma can be associated with a low anion gap because some myeloma proteins affect the calculation. But a low gap alone neither diagnoses cancer nor screens reliably for it. In a study of people already known to have monoclonal gammopathies, the gap was not a sensitive clue to those conditions. That study does not tell us the chance that a person with an isolated low result has cancer.

How do you improve low anion gap?

There is no single treatment for the calculated number. The useful next step is to confirm the result and understand its cause. If albumin is low or a medicine affects the result, the next decision depends on the person’s other results and clinical context. Do not change a prescribed medicine based on this number alone. Clinical review.

Which disorder would be a common cause of a decreased anion gap?

Low albumin, also called hypoalbuminemia, is a common biological cause of a decreased gap. It is a finding with several possible causes, rather than one diagnosis. Measurement error is the most common overall explanation for an unexpectedly low calculated result. Clinical review; MedlinePlus.

Sources

• Evaluating a low anion gap: A practical approach, Cleveland Clinic Journal of Medicine
• Anion Gap Blood Test, MedlinePlus
• The anion gap and routine serum protein measurements in monoclonal gammopathies, Clinical Journal of the American Society of Nephrology
• Basic Metabolic Panel (BMP), MedlinePlus
• Comprehensive Metabolic Panel (CMP), MedlinePlus

Medical disclaimer

This article is for education and does not replace care tailored to your results, symptoms, and health history.