Raised Lactate Interpreter: Type A, Type B or D-Lactate
Raised Lactate Interpreter: Type A, Type B or D-Lactate
Work out why a lactate is raised. Enter the lactate and the context — hypotension or vasopressors, infection, hypoxia, metformin, salbutamol, propofol, liver failure, thiamine risk, cancer, a recent seizure, short bowel — and the page separates type A (hypoperfusion or hypoxia) from type B causes and flags D-lactic acidosis, which the standard assay cannot detect. It applies the Sepsis-3 septic shock threshold and the Surviving Sepsis remeasurement advice.
Why is the lactate high?
Lactate + circulation, infection, drugs, context → type A, type B or D-lactateA 67-year-old with pyelonephritis has a blood pressure of 88/50 mmHg, not yet on vasopressors. Venous lactate 3.6 mmol/L.
Thresholds used
Septic shock (Sepsis-3): vasopressor for MAP ≥ 65 mmHg despite adequate fluid AND lactate > 2 mmol/L
Remeasure within 2–4 h if the first lactate is > 2 mmol/L (hour-1 bundle)
mmol/L = mg/dL × 0.111 (molar mass 90.08 g/mol)
- Type A
- inadequate oxygen delivery: shock, hypoxaemia, severe anaemia, CO or cyanide, ischaemia
- Type B
- no evidence of hypoperfusion: drugs, liver failure, thiamine deficiency, malignancy, inborn errors
- D-lactate
- the bacterial isomer; routine assays measure L-lactate only
Worked example
A 67-year-old with pyelonephritis has a blood pressure of 88/50 mmHg, not yet on vasopressors. Venous lactate 3.6 mmol/L.
Lactate 3.6 mmol/L (32 mg/dL): above 2, below 4
Hypotension without a vasopressor → Sepsis-3 septic shock criteria not met (yet); hypoperfusion present → type A
Hour-1 bundle: hypotension triggers 30 mL/kg crystalloid; remeasure the lactate within 2–4 hours
Causes of a raised lactate (Cohen–Woods classification, with D-lactate)
| Type | Mechanism | Examples |
|---|---|---|
| A | Oxygen delivery inadequate | Septic, cardiogenic or hypovolaemic shock; severe hypoxaemia; severe anaemia; CO or cyanide; mesenteric or limb ischaemia; cardiac arrest |
| B1 | Underlying disease | Liver failure, malignancy, thiamine deficiency, diabetic ketoacidosis |
| B2 | Drugs and toxins | Metformin, salbutamol and adrenaline, propofol, linezolid, NRTIs, toxic alcohols |
| B3 | Inborn errors | Mitochondrial disorders, pyruvate dehydrogenase deficiency |
| D-lactate | Bacterial fermentation in the gut | Short bowel, jejunoileal bypass — invisible to the routine L-lactate assay |
A high lactate is a question, not a diagnosis
Lactate is made whenever glycolysis outruns the mitochondria’s use of pyruvate, and cleared mainly by the liver and kidneys. A raised level therefore has two broad kinds of cause, named by Cohen and Woods in 1976: type A, where oxygen delivery is inadequate — shock, hypoxaemia, severe anaemia, ischaemia — and type B, where it is not, and the problem is a drug, a disease or an inborn error. The distinction matters because type A is treated by restoring the circulation, and chasing a type B lactate with more fluid does harm.
Sepsis is where the number is used most. The Sepsis-3 definition (Singer et al., 2016) makes a lactate above 2 mmol/L (18 mg/dL), together with a vasopressor needed to hold the mean arterial pressure at 65 mmHg despite adequate fluid, the clinical criteria for septic shock. The 2021 Surviving Sepsis guideline suggests measuring lactate in suspected sepsis and guiding resuscitation to lower it, but calls lactate neither sensitive nor specific enough to diagnose sepsis and not a direct measure of perfusion. The remeasurement interval — within 2 to 4 hours if the first value is above 2 mmol/L — comes from the 2018 hour-1 bundle, which also sets 4 mmol/L as a trigger for 30 mL/kg of crystalloid.
Two situations defeat the number. D-lactate, made by gut bacteria in short bowel syndrome, is not measured by the routine enzymatic or electrode assays, which are specific for L-lactate — so a patient with a high anion gap and a normal lactate can still have lactic acidosis. And glycolate from ethylene glycol is read as lactate by some blood gas analysers, so the gas lactate can be falsely high. Use the anion gap calculator and the delta ratio calculator to see whether the lactate accounts for the acidosis, and the lactate unit converter to convert units. This interpreter supports, and does not replace, clinical judgement.
Frequently asked questions
What lactate level defines septic shock?
Above 2 mmol/L (18 mg/dL), in a patient with sepsis who needs vasopressors to keep the mean arterial pressure at 65 mmHg or more despite adequate fluid resuscitation — the Sepsis-3 clinical criteria (Singer et al., JAMA 2016).
When should lactate be repeated in sepsis?
Within 2 to 4 hours if the first lactate is above 2 mmol/L, in the Surviving Sepsis Campaign’s 2018 hour-1 bundle. The 2021 guideline itself suggests guiding resuscitation to lower an elevated lactate but does not set an interval.
What is the difference between type A and type B lactic acidosis?
Type A comes from inadequate oxygen delivery — shock, hypoxaemia, severe anaemia, ischaemia. Type B occurs without it: drugs such as metformin, salbutamol and propofol, liver failure, thiamine deficiency, malignancy and inborn errors. Both can be present at once.
Why can D-lactic acidosis be missed?
Because routine lactate assays measure only L-lactate. D-lactate is produced by colonic bacteria in short bowel syndrome and needs a specific assay; the clue is an unexplained raised anion gap with episodes of confusion or ataxia.
Related calculators
References
- Singer M, Deutschman CS, Seymour CW, et al. The third international consensus definitions for sepsis and septic shock (Sepsis-3). JAMA. 2016;315(8):801–810.
- Evans L, Rhodes A, Alhazzani W, et al. Surviving Sepsis Campaign: international guidelines for management of sepsis and septic shock 2021. Intensive Care Med. 2021;47(11):1181–1247. Recommendations 3, 5, 7 and 8.
- Levy MM, Evans LE, Rhodes A. The Surviving Sepsis Campaign Bundle: 2018 update. Intensive Care Med. 2018;44(6):925–928. Table 1 (hour-1 bundle).
- Kraut JA, Madias NE. Lactic acidosis. N Engl J Med. 2014;371(24):2309–2319.
- Cohen RD, Woods HF. Clinical and Biochemical Aspects of Lactic Acidosis. Oxford: Blackwell Scientific; 1976. The type A / type B classification.
- Kowlgi NG, Chhabra L. D-lactic acidosis: an underrecognized complication of short bowel syndrome. Gastroenterol Res Pract. 2015;2015:476215.
- Hernández G, Ospina-Tascón GA, Damiani LP, et al. Effect of a resuscitation strategy targeting peripheral perfusion status vs serum lactate levels on 28-day mortality among patients with septic shock: the ANDROMEDA-SHOCK randomized clinical trial. JAMA. 2019;321(7):654–664.
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