A Simple Quantitative Bedside Test to Determine Methemoglobin
Study objective
Methemoglobinemia after pesticide poisoning is associated with a mortality of 12% in Sri Lanka. Treatment is complicated by the lack of laboratory facilities. We aimed to develop and validate a low-cost bedside test for quantitative estimation of clinically significant methemoglobin to be used in settings of limited resources.
Methods
A method to reliably produce blood samples with 10% to 100% methemoglobin was developed. Freshly prepared methemoglobin samples were used to develop the color chart. One drop (10 μL) of prepared methemoglobin sample was placed on white absorbent paper and scanned using a flatbed Cannon Scan LiDE 25 scanner. The mean red, green, and blue values were measured with ImageJ 1.37v. These color values were used to prepare a color chart to be used at the bedside. Interobserver agreement was assessed against prepared samples. The results from clinical use were compared with formal methemoglobin measurements.
Results
The red color value was linearly related to percentage methemoglobin (R2=0.9938), with no effect of absolute hemoglobin concentration. Mean interobserver (N=21) agreement and weighted κ for scanned methemoglobin spots using the color chart were 94% and 0.83, respectively. Mean interobserver (N=9) agreement and weighted κ for a freshly prepared methemoglobin sample with the chart were 88% and 0.71, respectively. Clinical use of the color chart also showed good agreement with spectrometric measurements.
Conclusion
A color chart can be used to give a clinically useful quantitative estimate of methemoglobinemia.
Please see page 185 for the Editor's Capsule Summary of this article.
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Supervising editor: Richard C. Dart, MD, PhD
Author contributions: FS wrote the first draft of the article, performed all laboratory analyses, analyzed the data, had access to all the data in the study, and had final responsibility for the decision to submit for publication. DMD and AHD designed and set up the study. NAB contributed ideas to design the study. NAB and AHD provided statistical advice on study design. All authors had a role in improving the study design and in reviewing and editing the final version of the article. FS takes responsibility for the paper as a whole.
Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article that might create any potential conflict of interest. The authors have stated that no such relationships exist. See the Manuscript Submission Agreement in this issue for examples of specific conflicts covered by this statement. This study was supported by the South Asian Clinical Toxicology Research Collaboration, which is funded by The Wellcome Trust/National Health and Medical Research Council International Collaborative Research Grant GR071669MA. The funding bodies had no role in analyzing or interpreting the data or writing the article.
Publication date: Available online October 8, 2009.
Reprints not available from the authors.
PII: S0196-0644(09)01281-5
doi:10.1016/j.annemergmed.2009.07.022
© 2009 American College of Emergency Physicians. Published by Elsevier Inc. All rights reserved.
