How to interpret lactate

Lactate as a Screening Tool for Critical Illness in a Pediatric Emergency Department

OBJECTIVES

Lactate has in some pediatric emergency departments (PEDs) gained acceptance as a screening tool for critical illness, with cut-off values of 2.0 to 2.5 mmol/L. We aimed to investigate if lactate could predict the need of acute resuscitation in patients in a PED.

PATIENTS AND METHODS

This retrospective observational cohort study included patients aged 0 to 17 years admitted to the PED at Copenhagen University Hospital in Denmark from January 1, 2019 to January 1, 2021. Patients were included if they had lactate measured as part of their routine blood sampling because of acute PED evaluation. Area under the receiver operating characteristic (ROC) curve (AUC) was calculated to assess the ability of lactate to predict the need of acute resuscitation. In patients without need of acute resuscitation, we calculated the lactate upper limit as the 95th percentile, and significant predictors were included in a multiple linear regression model.

RESULTS

A total of 1355 children were included. Fourteen (1%) children with a need of acute resuscitation had a median lactate of 1.7 mmol/L (interquartile range, 1.4-2.3) versus 1.6 mmol/L (interquartile range, 1.3-2.1) in children without need of resuscitation ( P > 0.05). The AUC for lactate to predict acute resuscitation was 0.56 (95% confidence interval, 0.54-0.59). In children without need of acute resuscitation, the 95th percentile of lactate was 3.2 mmol/L, and 392 (29.8%) had lactate greater than 2.0 mmol/L. Increasing age and venous sampling were associated with lower lactate. Lactate was not associated with sex, pediatric early warning score, or duration of hospital admission. The 95th percentile of lactate after inhaled beta-2-agonists was 5.0 mmol/L.

CONCLUSIONS

In children evaluated in a PED, lactate achieved a low AUC, suggesting a poor ability of predicting acute resuscitation. In children without need of acute resuscitation, the 95th percentile for lactate was 3.2 mmol/L, higher than the generally accepted cut-off values. This is important to recognize to avoid concern in otherwise clinically stable children. Our data did not support the use of lactate as a screening tool for early recognition of critical illness in a PED.

Can lactate be valuable in early diagnosis and prognosis of neonatal sepsis?

Background

Sepsis monitoring tissue perfusion is crucial for detecting circulatory failure early, implementing the right treatments, and assessing response. Insufficient oxygenation leads to a rise in lactate level and has been shown to be useful in predicting mortality and morbidity in newborns. There have not been many studies on how lactate measurement affects neonatal sepsis diagnosis and prognosis.

Aim

The aim of our study was to determine the impact of lactate on early diagnosis and prognosis in neonatal sepsis.

Materials and Methods

Eighty-seven newborns diagnosed with neonatal sepsis at a neonatal intensive care unit between January 2010 and July 2021 were included in the study. Venous blood gas, lactate, and C-reactive protein (CRP) levels and complete blood count on the first, second, and third day of hospitalization were noted. Lactate values were correlated with other variables to determine the impact of hyperlactatemia on morbidity and to determine factors affecting the length of stay. IBM SPSS Statistics version 22.0 for Windows was used to analyze the data (SPSS Inc., Chicago, IL, United States).

Results

A strong negative correlation between lactate and oxygenation and perfusion indicators (HCO3, BE, PaO2) during the therapeutic process was observed. With treatment, the initial measured lactate value decreased, and a significant increase in CRP and oxygen saturation was observed, which was interpreted as the observation of an early lactate response to infection before a CRP response. The initial lactate level, as well as the change in lactate levels, was not, however, significantly correlated with the length of stay.

Conclusion

Lactate can be used in the early diagnosis of neonatal sepsis and for determining prognosis.

Portable Near-Infrared Fluorometer for a Liposomal Blood Lactate Assay

In sepsis, plasma lactate is a key biomarker of disease severity, prognosis, and treatment success. However, the median time to result for clinical lactate tests is 3 h. We recently reported a near-infrared fluorescent (NIRF) blood lactate assay that relies on a two-step enzymatic reaction in a liposomal reaction compartment. This assay was optimized in human blood and was capable of quantifying lactate in fresh capillary blood from human volunteers at clinically relevant concentrations in 2 min. However, these studies were performed with a tabletop fluorescence plate reader. For translation to the point of care, the liposomal lactate assay needs to be combined with a small portable NIR fluorometer. Portable NIR fluorometers were successfully used for the analysis of skin and soil samples, but reports for blood metabolite assays are scarce. We aimed at testing the performance of the liposomal lactate assay in combination with a commercial small portable NIR fluorometer. First, we tested the fluorophore of the liposomal lactate assay using the NIR dye sulfo-cyanine 7; we observed strong fluorescence signals and high linearity. Second, we performed the liposomal lactate assay in lactate-spiked human arterial blood using the portable fluorometer as the detector and observed strong and highly linear lactate sensing at clinically relevant lactate concentrations after 2 min. Finally, spiking fresh mouse blood with three clinically relevant lactate concentrations led to a significantly different response to all three concentrations after 5 min. These results highlight the usefulness of the tested portable NIR fluorometer for the liposomal lactate assay and motivate a clinical evaluation of this rapid and easy-to-use lactate assay.