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 the 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 + [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 tab

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

Classification

  • 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

Pathophysiology

  • 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

Related Tests

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 J, Gans RO B. 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

Medical Reviewers

Last Update: April 2016