Lactate for Safely Screening Sepsis?

Fernando  et. al.  HELPFUL ONLY WHEN ELEVATED: INITIAL SERUM LACTATE IN STABLE EMERGENCY DEPARTMENT PATIENTS WITH SEPSIS IS SPECIFIC, BUT NOT SENSITIVE FOR FUTURE DETERIORATION Journal of Emergency Medicine, Vol. 54, No. 6, pp. 766–773. https://doi.org/10.1016/j.jemermed.2018.01.040 

BOTTOM LINE:

A lactate >4 in this prospective observational cohort study of almost 1000 patients with the “CMS” definition of sepsis was helpful in predicting “clinical deterioration” with an positive likelihood ratio (+LR) of 10.7 but only a negative likelihood ratio (-LR) of 0.8. Approximately 9% of patients with lactate >4 where sent home. However, a lactate of >2 only had a positive likelihood ratio (+LR) of 2 and a negative likelihood ratio(-LR) of 0.8. Lactate alone of >2 and less than 4 was not useful in predicting who had clinical deterioration or who didn’t. CMS uses a cutoff of 2 mmol/L

Ever since “sepsis” has become the only reason for a fever, the screening for mortality predictors has been the holy grail. Lactate has been promulgated as the “Lost Ark” of these biomarkers. However, just as with any single biomarker that has since been used it lacks the sensitivity and specificity we need and has rarely been tested agains physician gestalt. Remember that the THREE BIGGEST Sepsis trials all used a cutoff of lactate >4 after “fluid resuscitation”. Remember that CMS uses a lactate of >2…

Here, another article to remind us of the test characteristics of lactate arrives. In this very good prospective observational cohort study of adult ED patients satisfying the original sepsis definition the authors seek to find how good is lactate.  The authors looked at cutoff of both 2 and 4 mmol/L as the “discriminatory” zone of mortality. They do use a composite outcome of “clinical deterioration” which they define as: death, endotracheal intubation, vasoactive medication administration for a minimum of 1 h, noninvasive positive pressure ventilation (NIPPV) for a minimum of 1 h, or ICU admission for a minimum of 24 h. 985 patients met the original sepsis definition. Of these 84 patients (8.5% – shows you how good our sepsis definition is….) met the primary outcome of clinical deterioration and half of that 4% met the primary outcome while still in the ED. 

A lactate > 4.0 mmol/L  had a +LR of 10.7 (95% CI 6.3–18.3)and -LR 0.8 (95% CI, 0.7–0.9) for for predicting deterioration ( Sp 97.4% (95% CI 94.1–100%); Sn 27.4% (95% CI 17.8–36.9%). Of those patients with a lactate of 4 8.7% were discharged home and did not meet the primary outcome. 

A lacate of >2.0 mmol/L  had a +LR of 2.0 (95% CI 1.7–2.3) and -LR 0.5 (95% CI 0.4–0.7) for predicting deterioration, (Sn 67% (95% CI 55–76%); Sp of 66% (95% CI 63–69%). Of patients with a lactate < 2.0 mmol/L, 224 (56.1%) were discharged home and did not meet the primary outcome (which means half DID meet the primary outcome)

Of note those with a lactate 2.0-3.9 mmol/L 90% did NOT meet “clinical deterioration” and 10% did meet clinical deterioration 

Thus a lactate >4 was useful in predicting poor outcome but anything less was not useful either way (in reassuring no detioration or not).

This literature isn’t new but it is recent and should remind us that a normal lactate doesn’t help, nor does a lactate less than 4. Thanks CMS for more useless “meaningful use”…