Non-clinical sciences/Lab medicine · Acid–base

Metabolic acidosis (normal anion gap)

[object Object]

What it means

↓pH, ↓HCO₃, normal anion gap (hyperchloraemic) — bicarbonate is lost and replaced by chloride. Causes (HARDUPS): Hyperalimentation, Acetazolamide/Addison's, Renal tubular acidosis, Diarrhoea, Ureteroenterostomy, Pancreatic fistula, Saline excess. Diarrhoea and RTA are the big ones.

Worked example

Profuse diarrhoea: pH 7.28, HCO₃ 16, Cl 112, anion gap 9.

In the exam

After days of profuse diarrhoea a patient has pH 7.28, HCO₃ 16, a high chloride and a normal anion gap.

What settles it

Normal-gap = GI/renal HCO₃ loss (hyperchloraemic); raised-gap = added acid (ketones, lactate, toxins).

Classically confused with

Metabolic acidosis (raised anion gap)

Source: StatPearls — Acid-base