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Anion Gap (Blood) Calculated from Serum Ions

Published: August 9, 2026Updated: August 16, 2026

This test measures the difference between measured and calculated ions in your blood to help identify potential metabolic imbalances.

Quick summary

["The anion gap helps detect acid-base disorders, such as ketoacidosis or poisoning."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
73577-9
Short code
Anion Gap BldCoA Calculated.4Ions-sCnc
Synonyms
Anion Gap BldCoA Calculated.4Ions-sCnc
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
calculated-ions
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your doctor may order this test if you have symptoms like confusion, shortness of breath, or unusual fatigue, or if they suspect conditions like diabetic ketoacidosis, kidney failure, or exposure to toxins that alter ion balance.

What Does the Test Measure?

The test calculates the gap between sodium (a positively charged ion) and the sum of chloride and bicarbonate (both negatively charged ions) in your blood. This gap can reveal whether your body has too many or too few acids or bases.

How Is the Test Performed?

A small blood sample is drawn from a vein, typically in your arm. The sample is sent to a lab where ions are measured and the gap is calculated.

What Are Common Causes?

Elevated anion gaps may occur due to conditions like diabetic ketoacidosis, methanol poisoning, or severe kidney problems. A normal gap suggests other causes of acid-base imbalance, such as respiratory issues.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: The anion gap is a critical tool for diagnosing metabolic acidosis. An elevated gap often points to conditions that produce unusual acids (e.g., lactic acid, ketones) or toxins, while a normal gap may indicate metabolic or respiratory causes of acid-base disturbances.

Short name

Anion Gap

Frequently asked questions

What does an elevated anion gap mean?
An elevated anion gap suggests your blood may have excess acids not accounted for by typical lab measurements, which could signal conditions like diabetic ketoacidosis, poisoning, or kidney problems.
How often should I get this test?
Your doctor will determine how often you need this test based on your health condition, symptoms, or treatment plan. It’s often done as part of a broader evaluation.
Can I eat or drink before this test?
You may eat and drink normally unless instructed otherwise. Avoid alcohol or certain medications that could affect ion balance before the test.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy