Clinical Conundrums: Is an Arterial Lactate Necessary?

Bottom Line Up Top: A peripheral venous blood lactate can reliably be used instead of an arterial blood lactate as a marker of systemic tissue hypoperfusion and to measure response to treatment. 

Clinical Scenario: A 63 year old woman with diabetes, hypertension and rheumatoid arthritis presents with fever, back pain and dysuria. Vitals are HR 115, BP 110/63, RR 16, Temp 102.4, O2 sat 99% on RA. She is non-toxic appearing and well-perfused on examination. Labs reveal a urinalysis with + leukocyte esterase, + nitrates and > 100 WBCs. Her peripheral venous lactate is 1.8 mmol/L. Due to her age and comorbidities, you decide to admit her to the hospital but the admitting service requests an arterial lactate to determine if the patient is hypoperfused and requires a higher level of care.

What Your Gut Says: The arterial lactate is the better measure. Just get it, make sure it’s not elevated, and call back for admission.

What The Evidence Says:

Arterial blood sampling is typically avoided in the ED as it has been shown to cause significantly more pain than peripheral venous blood sampling and is associated with a variety of complications (Chauvin 2020). Additionally, numerous studies have shown close correlation between the arterial blood gas (ABG) and peripheral venous blood gas (VBG) in terms of pH, PCO2, HCO3 and base excess (Kelly 2010, Razi 2012, McCanny 2012, Zeserson 2018). The crew from Life in the Fastlane has a great post with details on this correlation (LITFL 2016). 

Lactate correlation is a bit more complicated. Studies show that at lactate levels < 2 mmol/L, there is excellent correlation between absolute values of arterial and peripheral venous samples. (Gallagher 1997, Samaraweera 2017, Oi 2022). Essentially, if the venous lactate is 1.5, the arterial lactate will be very close to that number. More importantly, if the peripheral venous lactate is in the normal range, the arterial lactate will also be in the normal range. These studies show less consistent absolute value correlation if the venous lactate exceeds 2 mmol/L. However, it is important for us to be clear about the question we are asking. If we want to know the exact lactate level in the arterial blood, we can only get that answer with an arterial sample. If, on the other hand, we want to use the lactate to help predict mortality or severity of disease, the exact value isn’t necessary; we simply need to know if an elevated venous lactate correlates with an elevated arterial lactate i.e. if the venous lactate is > 2 mmol/L is the arterial lactate also > 2 mmol/L? Here, once again, the data shows strong correlation; if the venous lactate is elevated, the arterial lactate will be elevated as well (Gallagher 1997, Theerawit 2018, Oi 2022). 

In terms of trending serum lactate levels to aid in assessment of clinical response to treatment, either peripheral venous or arterial lactate can be used. Due to the discrepancies in absolute value at elevated levels, it is advised to be consistent and serially follow lactates from the same source (i.e. if the first lactate is a peripheral venous sample, the repeat should be a peripheral venous sample as well).

Bottom Line: A normal peripheral venous lactate strongly correlates with a normal arterial lactate both in absolute value as well as in range. An elevated peripheral venous lactate strongly correlates with an elevated arterial lactate but absolute values over 2 mmol/L are not strongly correlated.

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  9. Theerawit P et al. The correlation between arterial lactate and venous lactate in patients with sepsis and septic shock. J Intensive Care Med 2018; 33(2): 116-20. PMID: 27502951

Post Created By: Anand Swaminathan MD (Instagram: @EMSwami)

Post Peer-Reviewed By: Salim R. Rezaie, MD (Twitter/X: @srrezaie)

Cite this article as: Anand Swaminathan, "Clinical Conundrums: Is an Arterial Lactate Necessary?", REBEL EM blog, July 11, 2024. Available at:

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