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Anion Gap (Blood) Calculated from Serum Ions

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

This test measures the difference between positively charged ions (like sodium) and negatively charged ions (like chloride and bicarbonate) in your blood. It helps identify conditions affecting acid-base balance.

Quick summary

["The anion gap helps diagnose metabolic imbalances, such as kidney issues or poisoning."]

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

Key facts at a glance

LOINC
73576-1
Short code
Anion Gap BldCoV Calculated.4Ions-sCnc
Synonyms
Anion Gap BldCoV 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 to check for conditions like diabetic ketoacidosis, kidney disease, or exposure to toxins that alter your blood chemistry. It’s often used alongside other blood tests to pinpoint problems with how your body handles acids and bases.

What Does an Anion Gap Tell Us?

A normal anion gap reflects balanced ions in your blood. A higher gap may suggest metabolic acidosis (too much acid) from causes like kidney failure or drug toxicity, while a lower gap could indicate conditions like hypercalcemia or certain blood disorders.

How Is This Test Performed?

A small blood sample is drawn from your arm. The lab analyzes the serum (liquid part of blood) to calculate the difference between sodium and the sum of chloride and bicarbonate ions.

What Are Common Causes of Abnormal Results?

Elevated anion gaps often occur due to metabolic acidosis, such as from diabetic ketoacidosis, lactic acidosis, or poisoning by substances like methanol or ethylene glycol. Low anion gaps are less common but may relate to hypercalcemia or certain blood disorders.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Anion Gap

Frequently asked questions

How often do I need this test?
This test is typically ordered as needed, often in response to symptoms like confusion, nausea, rapid breathing, or unexplained fatigue. Your doctor may also request it periodically if you have chronic conditions like kidney disease or diabetes.
What should I expect before the test?
No special preparation is usually needed, but avoid eating or drinking for at least 8 hours before the blood draw if instructed by your doctor. Wear a comfortable shirt with sleeves rolled up for easy access.
Can I take my usual medications before this test?
Yes, you can take your usual medications unless your doctor advises otherwise. Some medications (like certain diuretics or insulin) may affect blood chemistry, so always check with your healthcare provider.
  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