Validity and Reliability of Portable Blood Lactate Analyzers: A Systematic Review with COSMIN and GRADE Assessment

Portable blood lactate analyzers (PBAs) are increasingly used in sports and clinical contexts to assess physiological responses. Blood lactate is a critical biomarker for evaluating performance and metabolic thresholds. However, variability in device accuracy, sampling procedures, and calibration raises concerns about their validity and reliability. To systematically review peer-reviewed studies assessing the validity and reliability of commercially available PBAs compared to laboratory reference methods and to evaluate the methodological quality and certainty of evidence using the Consensus-based Standards for the selection of health Measurement INstruments (COSMIN) and Grading of Recommendations Assessment, Development and Evaluation (GRADE) frameworks. Following PRISMA 2020 guidelines, a systematic search was conducted across PubMed, Web of Science, Scopus, and SPORTDiscus. Of 253 records identified, 25 studies met the inclusion criteria. Validity was assessed using statistical measures such as Pearson’s correlation coefficient (r), concordance correlation coefficient (CCC), Bland–Altman limits of agreement (LoA), and mean absolute error (MAE). Reliability was evaluated using intraclass correlation coefficient (ICC), coefficient of variation (CV), and standard error of measurement (SEM). COSMIN and GRADE were used to rate study quality and evidence certainty. PBAs (e.g., Lactate Pro, Lactate Scout, Accutrend, Lactate Plus) showed strong correlations with reference standards (r = 0.95–0.99) and high reliability (ICC > 0.90; CV < 5%). However, systematic biases at higher lactate concentrations were common. Thirteen studies had high methodological quality. PBAs demonstrate strong reliability and moderate-to-high validity. Standardized protocols and improved calibration are needed to ensure consistency with laboratory-grade analyzers.