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Léguillier commented on the methodological biases in our recent study. We thank Léguillier for his interest and here we provide further clarification of the points mentioned in his letter.
Firstly we would like to clarify that the two handheld analysers used: Nova StatStrip Xpress Lactate Meter (Nova Biomedical, Waltham, USA) and Lactate Scout+ (EKF Diagnostics, Leipzig, Germany), were both calibrated, maintained and tested for quality control by their respective companies. In the absence of prior evidence of the superiority of one make of machine over another, we chose to compare two standard models.
Regarding the comment on the sample size, the calculated sample size using Bland-Altman method[1,2] was directed at the primary outcome measure, which was the agreement of the capillary blood lactate level measured by handheld lactate analyser when compared with the reference standard technique. Due to the diverse spectrum of patients seen in the ED, the range of lactate levels was representative of our daily clinical practice and was thus pragmatic. Furthermore, our sample size of 240 was larger than previous studies [3-7] ranging from 24 to 120 patients.
Lastly, we chose to use a cut off of 2 mmol/L as this is the upper limit of a normal lactate value. As we mentioned in the paper, screening ED venous lactate levels using a handheld analyser could provide information to shorten the time to identify patients at risk and to allow rap...
Lastly, we chose to use a cut off of 2 mmol/L as this is the upper limit of a normal lactate value. As we mentioned in the paper, screening ED venous lactate levels using a handheld analyser could provide information to shorten the time to identify patients at risk and to allow rapid clinical decision making for further treatment and therefore it was important to test the use of handheld blood capillary lactate analysers for screening purposes.
1. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1:307-10.
2. Altman DG. An introduction to medical statistics. 3rd ed. New York: Oxford University Press; 2000. p. 272-5.
3. Fauchere JC, Bauschatz AS, Arlettaz R, Zimmermann-Bar U, Bucher HU. Agreement between capillary and arterial lactate in the newborn. Acta Paediatr. 2002;91:78-81.
4. Datta D, Grahamslaw J, Gray AJ, Graham C. Capillary and Venous Lactate Agreement: a pilot prospective observational study. Emerg Med J. 2017;34:195-7.
5. Gaieski DF, Drumheller BC, Goyal M, Fuchs BD, Shofer FS, Zogby K. Accuracy of Handheld Point-of-Care Fingertip Lactate Measurement in the Emergency Department. West J Emerg Med. 2013;14:58-62.
6. Bouzat P, Schilte C, Vinclair M, Manhes P, Brun J, Bosson JL, et al. Capillary lactate concentration on admission of normotensive trauma patients: a prospective study. Scand J Trauma Resusc Emerg Med. 2016;24:82.
7. Léguillier T, Jouffroy R, Boisson M, Boussaroque A, Chenevier-Gobeaux C, Chaabouni T, Vivien B, Nivet-Antoine V, Beaudeux JL. Lactate POCT in mobile intensive care units for septic patients? A comparison of capillary blood method versus venous blood and plasma-based reference methods. Clinical Biochemistry. 2018 May 1;55:9-14.
In a recent issue, Graham et al  compared the transferability for blood lactate measurement between two assays. These authors raised two conclusions. First, a poor agreement between blood capillary and venous lactate measurements was reported; second, the use of blood capillary lactate measurement for diagnosis purposes was discouraged. From our point of view, this paper presents some methodological bias which do not allow the authors to draw those conclusions. We would like to advance three important considerations to support this claim.
Firstly, in the same way that laboratory analysers, handheld analysers must be tested for their analytical performances and submitted to periodic quality control check to ensure proper functioning of the equipment, accuracy of measurement and consistent readings. In the report , neither analytical performance nor quality control have been mentioned for the handheld analysers.
Secondly, to confirm a correct agreement between the measurements provided by different devices, the number of patients enrolled appears quite low. Indeed, the devices measurement range must be taken into account . Lactate values ranged from 0.7 to 5.38 mmol.l-1 , and 62.8% of the patients had lactate values < 2 mmol.l-1 while the devices had a measurement lactate range from 0.5 to 25 mmol.l-1. By this way, authors draw their conclusion only with the lower end of the range without considering high blood lactate values. We...
Secondly, to confirm a correct agreement between the measurements provided by different devices, the number of patients enrolled appears quite low. Indeed, the devices measurement range must be taken into account . Lactate values ranged from 0.7 to 5.38 mmol.l-1 , and 62.8% of the patients had lactate values < 2 mmol.l-1 while the devices had a measurement lactate range from 0.5 to 25 mmol.l-1. By this way, authors draw their conclusion only with the lower end of the range without considering high blood lactate values. We consider that the authors may conclude with a greater caution that their results exhibit a poor agreement between blood capillary lactate and references values.
Finally, the authors cited a report of Shapiro et al. to highlight the association between high blood lactate levels, severity of sepsis and poor outcome: low-risk of mortality < 2.2 mmol.l-1, intermediate-risk 2.3-5 mmol.l-1 and high-risk > 5 mmol.l-1 . The latter classification has previously been used to evaluate the concordance between lactate handheld analysers and laboratory analysers for diagnosis purposes [5,6]. The authors might use this classification to verify the agreement between handheld analysers and blood gas analyser results for the risk of poor outcome occurrence.
Thus, these restrictions suggest that Graham et al.  might more carefully conclude that “[their] results do not currently support the use of capillary lactate measurement for diagnostic purposes”.
1 Graham CA, Leung LY, Lo RS, et al. Agreement between capillary and venous lactate in emergency department patients: prospective observational study. BMJ Open 2019;9:e026109. doi:10.1136/bmjopen-2018-026109
2 Nichols JH, Christenson RH, Clarke W, et al. Executive summary. The National Academy of Clinical Biochemistry Laboratory Medicine Practice Guideline: evidence-based practice for point-of-care testing. Clin Chim Acta 2007;379:14–28; discussion 29-30. doi:10.1016/j.cca.2006.12.025
3 Vassault A, Grafmeyer D, de Graeve J, et al. Quality specifications and allowable standards for validation of methods used in clinical biochemistry. Ann Biol Clin (Paris) 1999;57:685–95.
4 Shapiro NI, Howell MD, Talmor D, et al. Serum lactate as a predictor of mortality in emergency department patients with infection. Ann Emerg Med 2005;45:524–8. doi:10.1016/j.annemergmed.2004.12.006
5 Léguillier T, Jouffroy R, Boisson M, et al. Lactate POCT in mobile intensive care units for septic patients? A comparison of capillary blood method versus venous blood and plasma-based reference methods. Clin Biochem 2018;55:9–14. doi:10.1016/j.clinbiochem.2018.03.006
6 Karon BS. Point-of-Care Lactate for Sepsis Detection: Reconsidering Accuracy, Precision, and Concordance Criteria. Point of Care 2017;16:131. doi:10.1097/POC.0000000000000141