Lactate (Blood)

Diagnostic Use

Lactate concentrations may be increased in:

Type I Lactic Acidosis: (increased lactate, no significant acidosis, normal lactate/pyruvate ratio).
Causes include muscular exercise, hyperventilation, glycogen storage disease, or severe anaemia.

Type II Lactic Acidosis: (increased lactate/pyruvate ratio, lowered pH)

Type IIa (hypoxic):
Caused by e.g. shock, heart failure, or haemorrhage. Blood lactate may indicate an imbalance between oxygen delivery and utilisation, but in most cases it offers no advantage over the measurement of arterial pH.

Splanchnic hypoperfusion is difficult to demonstrate in critically ill patients, and liver may have a reduced capacity to handle lactate, so the concentration of lactate may not be a good indicator of degree of tissue hypoxia. Isolated measurement is of little use. Serial measurements may be more useful, but only if raised concentrations can be attributed to tissue hypoperfusion.

Type IIb (metabolic/toxic):
The exact mechanisms are unknown but probably relate to mitochondrial function defect. Associated with e.g. renal infections, neoplasm, leukaemias/lymphoma, drugs/toxins (e.g. phenformin, methanol), sepsis before onset of shock, thiamine deficiency, inborn errors of metabolism, metabolic myopathies (e.g zidovudine induced).

Low (less than 2mmol/L), intermediate (2 to 4mmol/L, and high (>4mmol/L) venous lactate can be used to stratify mortality risk in those presenting with sepsis at the emergency department.

In suspected cyanide poisoning, based on anecdotal case reports / animal experiments, plasma lactate as a biologic indicator may suggest the diagnosis especially when no history is available. Plasma lactate levels that raise the possibility of cyanide poisoning:

≥10mmol/L in smoke inhalation victims (without severe burns)
≥8mmol/L in patients with cyanide exposure without concomitant carbon monoxide exposure

In ethylene glycol poisoning, there can be physiological rise in plasma lactate. In addition, because glycolic acid (a toxic metabolite of ethylene glycol) is similar to lactate, it reacts with some but not all lactate assays. By simultaneously testing the sample on 2 different lactate measurement systems, some qualitative information can be gathered. To obtain more information, contact on call chemical pathologist.

Reference Intervals