# Metabolic Acidosis: Gap, Cause, and Consequence

The gap narrows the cause; potassium, ammonium handling, and compensation identify additional processes and guide cause-specific treatment.

![Infographic: Metabolic Acidosis: Gap, Cause, and Consequence](https://urinenephrology.org/visual-reference/images/metabolic-acidosis.png?v=20261003c)

## Confirm the process

Low chemistry bicarbonate alone does not prove primary metabolic acidosis: respiratory alkalosis can also lower it. Obtain a blood gas when the distinction matters. Check pH and compare PaCO₂ with the expected compensation: 1.5 × HCO₃ + 8 ±2 mmHg.

## Calculate the gap

AG = Na − (Cl + HCO₃); use the laboratory reference and account for low albumin. High-gap acidosis directs attention to lactate, ketones, kidney failure, salicylate, and toxic alcohol exposure. Order the suspected acid or toxin directly when possible.

## Normal gap: GI loss or kidney defect?

Diarrhea and chloride-rich fluids are common causes. Low potassium suggests GI loss or selected tubular disorders; high potassium suggests impaired aldosterone activity, relevant drugs, or reduced kidney function. Urine pH alone cannot diagnose renal tubular acidosis.

## Ask whether ammonium excretion is appropriate

In normal-gap acidosis, increased urine ammonium supports an appropriate renal response to extrarenal bicarbonate loss. Direct measurement is preferable when available. The urine anion gap is confounded by unusual urinary anions, low distal sodium delivery, and CKD.

## Treat the generator of acid

Restore perfusion and treat sepsis for lactic acidosis; manage insulin deficiency and potassium in DKA; stop implicated drugs or obtain toxin-specific care. Bicarbonate is selective supportive treatment, not a replacement for controlling acid production or adequate ventilation.

## Separate chronic CKD from an ICU emergency

KDIGO 2024 suggests treatment to prevent clinically important acidosis, giving bicarbonate <18 mmol/L in adults as an example. Monitor BP, potassium, fluid status, and bicarbonate. Severe refractory acidemia with instability or other AKI complications may require KRT assessment.

## Supporting evidence

- [Official clinical guidance](https://kdigo.org/wp-content/uploads/2026/04/KDIGO-2024-CKD-Guideline.pdf)
- [PubMed 25295502](https://pubmed.ncbi.nlm.nih.gov/25295502/)

## Source lessons

- [metabolic acidosis](https://urinenephrology.org/2025_UDPA_Lectures_Live/electrolytes/acid-base/metabolic-acidosis.html)

Read alongside the full lessons; the findings and decisions shown here require the stated clinical context.