What does an elevated lactate level indicate?

Elevated blood lactate, above 2 millimoles per liter, indicates tissue hypoxia and anaerobic metabolism. When cells do not receive adequate oxygen, they shift to anaerobic glycolysis, producing lactate as a byproduct. Common causes include sepsis, shock, severe heart failure, respiratory failure, and tissue ischemia. Lactate levels above 4 millimoles per liter are associated with high mortality and indicate a need for aggressive resuscitation. In sepsis, serial lactate measurements guide treatment adequacy. Decreasing lactate levels indicate improving tissue perfusion.