Metabolic Acidosis

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Topics

Indications for Testing

  • Patient with altered mental status
  • Patient with initial laboratory results that indicate the presence of acidosis

Laboratory Testing

  • Metabolic panel (Na, K, Cl, HCO3-) and arterial blood gases
    • Expect decreased bicarbonate level on both tests, along with acidosis on arterial blood gases
    • Calculate anion and osmolar gaps to further aid in differential
      • Anion gap = [Na] - ([Cl] + [HCO3-])
        • Normal = 7-16 mmol/L
      • Osmolar gap = calculated plasma osmolality - measured plasma osmolality (2[Na+] + [glucose]/18 + [blood urea nitrogen (BUN)]/2.8)
        • Normal = -10 to +10 mOsm/kg
  • Based on clinical scenario and anion gap calculation, further testing may be appropriate
    • Glucose – evaluate for diabetes mellitus (DM)
    • BUN/creatinine – evaluate for renal failure
    • Lactate/pyruvate levels – evaluate for lactic acidosis
    • Beta-hydroxybutyrate acid – evaluate for DM, starvation
    • Ethanol levels – evaluate alcohol poisoning
    • Microscopic examination of urine for crystals to differentiate methanol from ethylene glycol
      • Methanol and ethylene glycol serum levels may also be necessary
    • Salicylate levels – evaluate for salicylate poisoning
    • Anion gap may also be elevated by toxicants such as acetaminophen, iron, toluene, phenformin, paraldehyde, arsenic
    • Other testing (serum drug levels) based on results of above testing

Differential Diagnosis

  • Refer to the different types of metabolic acidosis in the Background section

Metabolic acidosis, a condition in which there is excess buildup of acid in body fluids, is heralded by a decreased concentration of plasma bicarbonate.


  • Type of metabolic acidosis is based on anion/osmolar gap calculation
    • Anion gap = [Na] - ([Cl ] + [HCO3-])
    • Osmolar gap = calculated plasma osmolality - measured plasma osmolality (2[Na+] + [glucose]/18 + [BUN]/2.8)
    • Osmolar gap may be used to differentiate between different types within high anion gap acidosis


  • Excess production of organic acids exceeds rates of elimination
    • Beta-hydroxybutyrate and acetoacetic acid production during diabetic acidosis
    • Lactic acid production during lactic acidosis
  • Reduced excretion of acids
    • Renal failure
    • Renal tubular acidosis
  • Excessive loss of bicarbonate
    • Renal losses
    • Gastrointestinal losses (eg, diarrhea)
Tests generally appear in the order most useful for common clinical situations. Click on number for test-specific information in the ARUP Laboratory Test Directory.

Basic Metabolic Panel 0020399
Method: Quantitative Ion-Selective Electrode/Quantitative Enzymatic/Quantitative Spectrophotometry

Osmolality, Serum or Plasma 0020046
Method: Freezing Point

Lactic Acid, Plasma 0020045
Method: Enzymatic

Beta-Hydroxybutyric Acid 0080045
Method: Quantitative Enzymatic

Alcohols 0090131
Method: Quantitative Gas Chromatography

Ethylene Glycol 0090110
Method: Quantitative Enzymatic

Salicylate Assay 0090251
Method: Spectrophotometry

General References

Ayers P, Warrington L. Diagnosis and treatment of simple acid-base disorders. Nutr Clin Pract. 2008; 23(2): 122-7. PubMed

Berend K, de Vries AP, Gans RO. Physiological approach to assessment of acid-base disturbances. N Engl J Med. 2014; 371(15): 1434-45. PubMed

Casaletto JJ. Differential diagnosis of metabolic acidosis. Emerg Med Clin North Am. 2005; 23(3): 771-87, ix. PubMed

Englehart MS, Schreiber MA. Measurement of acid-base resuscitation endpoints: lactate, base deficit, bicarbonate or what? Curr Opin Crit Care. 2006; 12(6): 569-74. PubMed

Kellum JA. Acid-base disorders and strong ion gap. Contrib Nephrol. 2007; 156: 158-66. PubMed

Morris CG, Low J. Metabolic acidosis in the critically ill: part 1. Classification and pathophysiology. Anaesthesia. 2008; 63(3): 294-301. PubMed

Morris CG, Low J. Metabolic acidosis in the critically ill: part 2. Causes and treatment. Anaesthesia. 2008; 63(4): 396-411. PubMed

Palmer BF, Clegg DJ. Electrolyte and Acid-Base Disturbances in Patients with Diabetes Mellitus. N Engl J Med. 2015; 373(6): 548-59. PubMed

Wilson JF. In clinic. Diabetic ketoacidosis. Ann Intern Med. 2010; 152(1): ITC1-1 - ITC1-15, quiz ITC1-16. PubMed

References from the ARUP Institute for Clinical and Experimental Pathology®

Gleicher N, McCulloh DH, Kushnir VA, Ganguly N, Barad DH, Goldman KN, Kushnir MM, Albertini DF, Grifo JA. Is there an androgen level threshold for aneuploidy risk in infertile women. Reprod Biol Endocrinol. 2015; 13: 38. PubMed

Lu J, Pulsipher BS, Grenache DG. Development of an enzymatic assay to measure lactate in perchloric acid-precipitated whole blood Clin Chim Acta. 2015; 444: 208-11. PubMed

Medical Reviewers

Last Update: July 2017