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Clinical Chemistry 45: 1313-a-1314-a, 1999;
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(Clinical Chemistry. 1999;45:1313-1314.)
© 1999 American Association for Clinical Chemistry, Inc.

Letters

Comment on the Overestimation of Methemoglobin Concentrations in Neonatal Samples with the Chiron 800 System CO-Oximeter Module

Marinus H. de Keijzera

a Author for correspondence. Fax 31 243541743; e-mail R.deKeijzer{at}ckcl.azn.nl

Rob Brandts and Belinda A.J. Giesendorf

Central Clinical Chemical Laboratory, University Hospital St. Radboud Nijmegen 564 CKCL, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands


To the Editor:

We wish to comment on the Technical Brief of Lynch et al. (1), who reported overestimation of methemoglobin concentrations in neonatal samples containing fetal hemoglobin and analyzed with the Chiron 800 system CO-oximeter. Overestimation of methemoglobin in the presence of fetal hemoglobin may have serious implications, with the possibility of premature termination of nitric oxide treatment. In our hospital, >1000 methemoglobin analyses are performed annually on request of our neonatal intensive care unit. These measurements have been performed with a CIBA Corning 270 CO-oximeter and, at present, are also performed with a Chiron 865 blood gas analyzer equipped with a CO- oximetry module (Chiron Diagnostics NV).

We decided to investigate this alarming report and used both analyzers to measure methemoglobin concentrations in three sets of samples. The first set consisted of 10 samples from our neonatology department. In these samples, the concentration of fetal hemoglobin was 65% or higher. The second and third sets of samples consisted of adult blood and umbilical cord blood, respectively, collected in heparin-containing tubes and divided into two portions. In one portion of each sample, 100% methemoglobin was obtained by adding potassium nitrite (2). The other portion was not treated (<2% methemoglobin). All portions were washed with saline several times and subsequently used to produce samples with nominal percentages of methemoglobin of 2–25%. Samples were measured within 2 min on both blood gas analyzers. The results are given in Table 1 .


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  		Table 1. Percentages of methemoglobin measured with the Corning 270 and the Chiron 865 blood gas analyzer.

In the samples from neonates, no statistical differences between the methemoglobin percentages mea-sured with the Corning 270 and the Chiron 865 analyzer were observed (paired t-test, P <0.05). The results obtained for adult blood and umbilical cord blood revealed that measurement of 5% methemoglobin or less was not markedly influenced by the presence of fetal hemoglobin on both analyzers. Above 10% methemoglobin, the Corning 270 blood gas analyzer has a tendency to underestimate the amount of methemoglobin compared with the Chiron 865 analyzer. This, however, was not influenced by the presence or absence of fetal hemoglobin because the discrepancy was present in adult blood as well as umbilical cord blood. These findings were also reported by Lynch et al. (1).

The divergence between our results and those of Lynch et al. in the low methemoglobin range (<5%) may be explained by the different software versions that were used. The analyzer used by Lynch et al. was equipped with software that uses 10 wavelengths to calculate the various hemoglobin fractions. The new software program (Ver. 4.4c) implemented in our Chiron 865 blood gas analyzer uses 40 wavelengths, including wavelengths in the optimal region for the measurement of methemoglobin.

We conclude that the Chiron 865 analyzer equipped with the 40-wavelength software (Ver. 4.4c) is suitable for measuring methemoglobin concentrations in the clinically relevant range, even in samples with high concentrations of fetal hemoglobin.


Acknowledgments

We thank H.E. Aaldring for expert technical support.


References

  1. Lynch PLM, Bruns DE, Boyd JC, Savory J. Chiron 800 system CO-oximeter module overestimates methemoglobin concentrations in neonatal samples containing fetal hemoglobin. Clin Chem 1998;44:1569-1570. [Free Full Text]
  2. Speakman ED, Boyd JC, Bruns DE. Measurement of methemoglobin in neonatal samples containing fetal hemoglobin. Clin Chem 1995;41:458-461. [Abstract/Free Full Text]




This Article
Right arrow Extract Freely available
Right arrow Submit an electronic Letter to
the Editor about this paper
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
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Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via ISI Web of Science (1)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by de Keijzer, M. H.
Right arrow Articles by Giesendorf, B. A.J.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by de Keijzer, M. H.
Right arrow Articles by Giesendorf, B. A.J.
Related Collections
Right arrow General Clinical Chemistry
Right arrow Pediatric Clinical Chemistry
Right arrow Drug Monitoring and Toxicology
Right arrow Hematology

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