Can Lactic Acid Be Drawn from a Peripheral Line?
Yes, lactic acid can be drawn from a peripheral intravenous line, though arterial sampling remains the gold standard and peripheral venous values may differ from arterial values by approximately 0.5-0.6 mmol/L. 1, 2
Understanding the Difference Between Sampling Sites
Arterial vs. Peripheral Venous Lactate
Peripheral venous lactate (PV-LACT) runs approximately 0.54 mmol/L higher than arterial lactate (A-LACT) on average, with 95% limits of agreement ranging from -0.11 to 1.18 mmol/L 2
A separate study found the mean difference (bias) between arterial and venous lactate was -0.6 mmol/L, with limits of agreement from -1.7 to 0.6 mmol/L 1
The misclassification rate between arterial and venous sampling is approximately 8%, meaning one measurement may fall below 1.8 mmol/L while the other exceeds 2.2 mmol/L 1
Both arterial and peripheral venous lactate demonstrate similar prognostic value for predicting poor outcomes (in-hospital death or ICU admission >72 hours), with identical area under the curve values of 0.67 1
Central Venous vs. Arterial Lactate
Central venous lactate (Lact(cv)) and arterial lactate collected within a 30-minute interval are highly interchangeable for clinical practice 3
Central venous lactate with a cutoff of 2 mmol/L can predict arterial lactate above 2 mmol/L with sensitivity >92% and specificity >90% 3
The area under the curve for central venous lactate to predict arterial lactate above 2 mmol/L is 0.98 (95% CI: 0.97-0.99) 3
Practical Clinical Approach
When Peripheral Venous Sampling Is Acceptable
Use peripheral venous lactate for initial screening and risk stratification in emergency department patients, recognizing it may run slightly higher than arterial values 2
Peripheral venous lactate is particularly useful when arterial access is not available or when rapid assessment is needed 2
Serial measurements from the same site (peripheral venous) can effectively track lactate clearance and response to therapy 1
When to Prefer Arterial or Central Venous Sampling
For critically ill patients requiring precise lactate measurements to guide aggressive resuscitation (especially when lactate is near clinical decision thresholds of 2 or 4 mmol/L), arterial or central venous sampling is preferred 1, 3
When central venous access is already in place for ScvO2 monitoring, use central venous blood for lactate measurement as it closely approximates arterial values 3
In septic shock patients on vasopressors where lactate >2 mmol/L is part of the diagnostic criteria, arterial or central venous sampling provides more reliable values 1, 3
Critical Sampling Technique Considerations
Avoiding Contamination from IV Lines
Never draw lactate samples from a line that is being used for glucose-containing infusions, as even minimal contamination can cause dangerous sampling errors 4, 5
Use only sodium chloride 0.9% (with or without heparin) as flush solution for any line from which blood samples will be drawn 4, 5
When using arterial lines, employ 'closed' sampling systems to minimize contamination risk and blood wastage 4, 5
Proper Collection Technique
Collect lactate samples in prechilled fluoride-oxalate tubes, transport on ice to the laboratory, and process within 4 hours of collection 6
Draw samples without tourniquet application or fist-clenching, as these can artificially elevate lactate levels 6
Ensure adequate dead space removal when sampling from any indwelling catheter to prevent flush solution contamination 5
Common Pitfalls to Avoid
Do not assume peripheral venous and arterial lactate are identical—expect peripheral venous values to run 0.5-0.6 mmol/L higher 1, 2
Do not switch between sampling sites during serial monitoring without accounting for the systematic difference between sites 1
Do not draw lactate from lines carrying any glucose-containing solutions, as this creates serious risk of falsely elevated values that could lead to inappropriate insulin administration 4, 5
Be aware that the 8% misclassification rate means approximately 1 in 12 patients may be incorrectly categorized when comparing peripheral venous to arterial values around clinical decision thresholds 1
Remember that while peripheral venous lactate is acceptable for screening, patients with values near critical thresholds (2 or 4 mmol/L) may benefit from confirmatory arterial or central venous sampling 1, 3