Lactic acidosis is caused by an increase in blood concentrations of L-lactate. This may occur as a normal physiologic response or it may reflect serious underlying disease.


Testing may be performed on arterial or venous blood samples, which have different reference ranges.


Suspect lactic acidosis when the anion gap is > 18 mmol/L in the absence of another explanation.

Metabolic Features

Lactate to Pyruvate Ratio



increased lactic acid but without acidosis



Type I

increased lactic acid with acidosis


hypoxia-related (decreased oxygen delivery)

Type IIA

increased lactic acid with acidosis


metabolic (drugs or toxin, concurrent disease, inborn error metabolism)

Type IIB


Criteria for Type II (Sacks, 1999):

(1) increased lactate concentration (> 5 mmol/L)

(2) pH < 7.25


Causes of Type I:

(1) muscular exercise

(2) hyperventilation

(3) glucagon administration

(4) glycogen storage disease

(5) severe anemia

(6) insulin administration

(7) Reye's syndrome


Causes of Type IIA:

(1) acute hemorrhage

(2) acute heart failure

(3) circulatory shock

(4) severe hypoxemia

(5) extracorporeal circulation

(6) cardiac arrest


Causes of Type IIB - drugs or toxins:

(1) ethanol

(2) phenformin

(3) fructose or sorbitol infusion

(4) recovery from diabetic ketoacidosis


Causes of Type IIB - inborn errors of metabolism

(1) glycogen storage disease type I

(2) defects in pyruvate metabolism


Causes of Type IIB - concurrent disease:

(1) mild uremia

(2) infection (pyelonephritis, subacute bacterial endocarditis, poliomyelitis)

(3) cirrhosis

(4) third trimester of pregnancy

(5) severe vascular disease

(6) leukemia or neoplastic disease

(7) anemia

(8) thiamine deficiency

(9) metabolic myopathy



• Lactate levels may be increased by improper collection, handling and testing.


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