What Does Lactate Mean on a Blood Test?

What it means

Cells normally use oxygen to turn sugar into energy. When they cannot get enough oxygen, or cannot use it properly, they switch to a back-up method that produces lactate. The liver and kidneys usually clear lactate quickly, so a high level means it is being made faster than it can be removed. A raised lactate in someone who is very unwell can be a sign of a medical emergency, such as sepsis or shock, which needs urgent hospital care.

Lactate is often measured on a blood gas machine in the emergency department or on a ward, and the result comes back within minutes. Doctors use it to judge how seriously ill someone is and whether blood and oxygen are reaching the tissues well. They often repeat it to see whether it is coming down with care. A single number is read alongside blood pressure, heart rate, breathing and other results.

Lactate and lactic acidosis are related but not the same. Lactate is the measurement. Lactic acidosis is when lactate builds up enough to make the blood more acidic than usual. Lactate is also unrelated to lactose, the sugar in milk.

Where you may see it

• Blood gas printouts in the emergency department, often labelled "Lac"
• Sepsis screening forms and hospital observation charts
• Intensive care results, sometimes checked several times a day
• Discharge summaries describing a hospital stay for infection or shock