It's a blood prick test.I have not taken the trouble to search through but do we know how lactate is being measured in these devices? Is it on optical spectrum or is blood actually sampled or what?
Reliability and Accuracy of Six Hand-Held Blood Lactate Analysers
The monitor I used rates well at both high and low lactate levels in that study.These devices interpret the electrical signal produced as a result of the reaction between lactate in the blood and the enzyme lactate oxidase on the inserted sensor. The voltage signal corresponds directly to the lactate concentration of the sample.