Evaluation of metabolic acidosis

Last reviewed: August 2019

Last updated: June 2018

Summary

The presence of metabolic acidosis is a clue to the possible existence of several underlying medical conditions. Arterial pH <7.35 defines acidosis. Metabolic acidosis is indicated by a decrease in the plasma bicarbonate level and/or a marked increase in the serum anion gap (AG).

Metabolic acidosis may occur due to the following reasons:

Addition of strong acid that is buffered by and consumes bicarbonate ion
Loss of bicarbonate ion from the body fluids, usually through the GI tract or kidneys
Rapid addition to the extracellular fluid of a nonbicarbonate solution.

Differentiating between the causes of metabolic acidosis begins with calculation of serum AG. Serum AG is calculated by subtracting the sum of major measured anions, chloride (Cl) and bicarbonate (HCO3), from the major measured cation, sodium (Na+).

AG = Na - (Cl + HCO3)

Normal serum AG is due to the difference between unmeasured anions such as sulfate (SO4), phosphate (PO4), albumin, and organic anions, and unmeasured cations such as potassium (K+), magnesium (Mg+), and calcium (Ca2+). Plasma proteins also play a role in maintaining normal serum AG. [1]

Differentials

Common

GI loss of bicarbonate
Renal loss of bicarbonate - renal tubular acidosis type 1 and 2
Renal tubular acidosis type 4
Diabetic ketoacidosis
Alcohol ketoacidosis
Ingestion of toxic substances
Acetaminophen ingestion (5-oxoproline toxicity)
Salicylate intoxication
Lactic acidosis
Acute renal failure
Chronic renal failure

Full details

Uncommon

Addition of acid

Full details

Contributors

Authors VIEW ALL 

Dinkar Kaw, MD

Professor of Medicine

Division of Nephrology

Department of Medicine

University of Toledo College of Medicine

Toledo

Disclosures

DK declares that he has no competing interests.

Acknowledgements

Dr Dinkar Kaw would like to gratefully acknowledge Dr Joseph I. Shapiro, a previous contributor to this monograph. JIS declares that he has no competing interests.

Peer reviewers VIEW ALL 

Tausif Zar, MD

Staff Nephrologist

Division of Nephrology

Department of Medicine

Southern Arizona Veterans Affairs Health Care System

Tucson

Disclosures

TZ declares that he has no competing interests.

Andrew Fenves, MD

Professor of Medicine

Baylor University Medical Center

Dallas

Disclosures

AF declares that he has no competing interests.

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Evaluation of metabolic acidosis

Summary

Differentials

Common

Uncommon

Contributors

Authors VIEW ALL 

Dinkar Kaw, MD

Disclosures

Acknowledgements

Peer reviewers VIEW ALL 

Tausif Zar, MD

Disclosures

Andrew Fenves, MD

Disclosures

View PDF