Metabolic Acidosis

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Content

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 – rule out diabetes mellitus (DM)
    • BUN/creatinine – rule out renal failure
    • Lactate/pyruvate levels – rule out lactic acidosis
    • Beta-hydroxybutyrate acid – suggests DM, starvation
    • Ethanol levels – rule out 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 – rule out 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.


  • 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)


  • 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)

Indications for Laboratory Testing

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

Additional Tests Available

Bicarbonate (HCO3), Urine 0020245
Method: Enzymatic


Aids in diagnosis of metabolic acidosis

Electrolytes, Urine 0020498
Method: Quantitative Ion-Selective Electrode


Aids in differentiating renal from nonrenal causes of non-anion-gap metabolic acidosis

Test includes sodium, potassium, chloride, creatinine

Pyruvic Acid 0080310
Method: Quantitative Enzymatic


Differential diagnosis of lactic acidosis

An isolated pyruvic acid concentration has little clinical value

Preferred test is lactate to pyruvate ratio, whole blood, which reports concentrations for lactate, pyruvate, and L:P ratio on the same specimen

Calcium, Serum or Plasma 0020027
Method: Quantitative Spectrophotometry

Carbon Dioxide, Serum or Plasma 0020004
Method: Quantitative Enzymatic

Chloride, Serum or Plasma 0020003
Method: Quantitative Ion-Selective Electrode


Screening test to evaluate kidney function

Creatinine, Serum or Plasma 0020025
Method: Quantitative Enzymatic


Screening test to evaluate kidney function

Methanol 0090165
Method: Quantitative Gas Chromatography

Potassium, Plasma or Serum 0020002
Method: Quantitative Ion-Selective Electrode

Sodium, Plasma or Serum 0020001
Method: Quantitative Ion-Selective Electrode

Urea Nitrogen, Serum or Plasma 0020023
Method: Quantitative Spectrophotometry


Screening test to evaluate kidney function

Ethanol, Serum or Plasma - Medical 0090120
Method: Quantitative Gas Chromatography/Enzymatic


Serum test to identify acute alcohol ingestion

Arsenic, Urine with Reflex to Fractionated 0025000
Method: Quantitative High Performance Liquid Chromatography/Quantitative Inductively Coupled Plasma-Mass Spectrometry


Urine is preferred specimen for arsenic testing

Differentiates between toxic inorganic, organic, and methylated forms of arsenic

Reflex pattern – if total arsenic concentration is between 35-2000 ug/L, then arsenic, fractionated, will be added to determine the proportion of organic, inorganic, and methylated forms

Glucose, Plasma or Serum 0020024
Method: Quantitative Enzymatic

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 A, Gans R. Physiological approach to assessment of acid-base disturbances. N Engl J Med. 2014; 371(15): 1434-45. PubMed

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

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

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

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

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

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

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

Medical Reviewers

Last Update: January 2016