Anion Gap Calculator

Frequently Asked Questions

What is the normal anion gap range?

The conventional normal range is 8 to 12 mEq/L. Some laboratories using newer analyzers report a slightly lower range of 6 to 10 mEq/L. Always compare results to your laboratory's reference range, as methods and electrolyte analyzer calibrations vary.

How do I read the values from a lab report?

Look for sodium (Na), chloride (Cl), and bicarbonate (HCO3 or CO2 - note that the reported CO2 on a metabolic panel is total CO2, which approximates bicarbonate) in the electrolyte section of a basic or comprehensive metabolic panel. Enter all three in mEq/L.

What if my anion gap is borderline, around 12 to 15?

A mildly elevated gap can be seen with dehydration (hemoconcentration), mild lactic acidosis, or early DKA. It should be interpreted with blood pH, lactate, ketones, and clinical context. Borderline values do not always indicate pathology but warrant further evaluation.

Can I use this calculator to diagnose myself?

No. This tool provides an educational estimate only. Metabolic acidosis and its causes require clinical assessment, additional laboratory tests (blood gas, lactate, ketones, osmolar gap), and medical judgment to diagnose and treat. Always consult a qualified healthcare provider.

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General information only. Not medical advice.

Health & Medical Disclaimer: General information only. Not medical advice.

This calculator provides general health information only and is not medical advice. Results do not replace professional medical evaluation or diagnosis. Consult a licensed healthcare provider before making health decisions. Always seek immediate medical attention for emergencies.

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How This Calculator Works

The serum anion gap (AG) estimates the concentration of unmeasured anions in plasma. It is calculated with the formula: AG = Na&sup+; − (Cl&sup- + HCO&sub3;&sup-), where sodium (Na), chloride (Cl), and bicarbonate (HCO3) are all measured in milliequivalents per liter (mEq/L). Enter the three values from a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP) and the calculator returns the gap and classifies it as high, normal, or low against the conventional 8 to 12 mEq/L reference range. The result is a clinical screening tool, not a diagnosis.

Why the Anion Gap Matters

In healthy blood, the total positive charges (cations) equal the total negative charges (anions). Sodium accounts for most measured cations; chloride and bicarbonate account for most measured anions. The gap between sodium and the sum of chloride plus bicarbonate represents unmeasured anions - mainly albumin, phosphate, sulfate, and organic acids. When an acid accumulates, it consumes bicarbonate and widens the gap, signaling a high-anion-gap metabolic acidosis (HAGMA). Identifying a HAGMA focuses the differential diagnosis on conditions that generate acids rather than on conditions that waste bicarbonate.

Causes of High Anion Gap Acidosis

The MUDPILES mnemonic captures the main causes: Methanol poisoning, Uremia (severe kidney failure), Diabetic ketoacidosis (DKA), Propylene glycol toxicity, Iron or Isoniazid toxicity, Lactic acidosis, Ethylene glycol poisoning, Salicylate toxicity. Lactic acidosis from shock, sepsis, or liver failure is the most common cause in hospitalized patients. DKA is the most common in the ambulatory setting. A gap above 20 mEq/L strongly suggests an organic acid accumulation and warrants urgent evaluation.

Normal and Low Anion Gap Acidosis

A normal-anion-gap metabolic acidosis (NAGMA, also called hyperchloremic acidosis) occurs when bicarbonate is lost while chloride rises to maintain electroneutrality. Common causes include diarrhea, renal tubular acidosis, and excessive normal saline administration. A low anion gap (below 8 mEq/L) is less common and may reflect hypoalbuminemia (since albumin is a major unmeasured anion), multiple myeloma with cationic immunoglobulins, severe hyperlipidemia, or laboratory error. When albumin is low, the corrected anion gap formula adds 2.5 mEq/L for each 1 g/dL decrease in albumin below 4 g/dL.

Albumin-Corrected Anion Gap

Because albumin is the primary unmeasured anion, hypoalbuminemia artificially lowers the gap. In critically ill patients, albumin is often low, which can mask a true HAGMA. The albumin-corrected anion gap formula is: corrected AG = measured AG + 2.5 × (4 − albumin in g/dL). For example, if the measured AG is 10 mEq/L but albumin is 2 g/dL, the corrected gap is 10 + 2.5 × (4 − 2) = 10 + 5 = 15 mEq/L, revealing a true HAGMA that the uncorrected value obscured. This calculator uses the uncorrected formula; if albumin is known and abnormal, apply the correction manually.

Important Note

This calculator is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider before making any health-related decisions. The anion gap is a screening tool that must be interpreted alongside clinical findings, the full metabolic panel, blood gas results, and the patient's history. Only a licensed clinician can diagnose and treat acid-base disorders.

Anion Gap Calculator

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