Anion Gap: What Your Result Means

What is Anion Gap?

The anion gap (typically 8–12 mEq/L) represents unmeasured anions — the negative charge not accounted for by chloride and bicarbonate. The gap WIDENS when pathological unmeasured anions accumulate: lactic acid, ketones, uremic acids, salicylate, methanol/ethylene glycol metabolites.

Typical reference interval: Approximately 8–12 mEq/L (varies by laboratory; modern methods may have lower reference, ~3–10).. Laboratories differ — the interval printed on YOUR report always governs.

If your Anion Gap is high

Common reasons Anion Gap runs above the reference interval:

• Lactic acidosis — tissue hypoperfusion, sepsis, seizures — the most common high-gap acidosis
• Diabetic ketoacidosis — acetoacetate and beta-hydroxybutyrate accumulation
• Alcoholic ketoacidosis — starvation+alcohol metabolism generates ketones
• Renal failure — uremic acid retention
• Toxins — methanol, ethylene glycol, salicylates, paraldehyde
• Propylene glycol infusion — iatrogenic cause in ICU settings

If your Anion Gap is low

Common reasons Anion Gap runs below the reference interval:

• Laboratory error — the most common cause — check for spurious electrolyte values
• Multiple myeloma — cationic paraproteins reduce the gap
• Hypoalbuminemia — albumin is an unmeasured anion; low albumin LOWERS the gap (correct for albumin: add 2.5 mEq/L per 1 g/dL albumin deficit)

Symptoms worth knowing

Belongs to underlying acidosis: Kussmaul breathing, nausea, vomiting, lethargy progressing to stupor. The GAP itself is diagnostic, not symptomatic.

What usually happens next

1. High-gap acidosis → lactate, ketones, BUN/creatinine, osmolar gap (for toxins)
2. Normal-gap acidosis → stool history, urinary anion gap, consider renal tubular acidosis
3. Albumin-correct anion gap essential in hypoalbuminemic patients (ICU, malnutrition)

Frequently asked questions about Anion Gap results