However, the enzyme is isomer-specific so that production and metabolism of D-lactate requires D-LDH and L-lactate requires L-LDH. Mammalian cells only contain L-LDH so that in humans the lactate produced is almost exclusively L-lactate. Carbohydrate-fermenting bacterial species (e.g. Lactobacillus spp) have by contrast both enzymes and therefore the capacity to produce both D-lactate and L-lactate. Some species produce only D-lactate, some only L-lactate and others both forms.
Tissue hypoxia, which is the result of inadequate perfusion of tissues and/or reduced blood oxygen (hypoxemia), is a common feature of many kinds of critical illness so that lactate measurement is most frequently used to monitor tissue oxygenation in the critically ill patients. L-lactate within the reference range is considered reliable evidence that tissues are adequately oxygenated.