Lab Med Online.  2013 Jan;3(1):1-5. 10.3343/lmo.2013.3.1.1.

Utilization of Mean Peroxidase Index for Discrimination of Pseudoneutropenia

• Oh AC
• Lee JK
• Hong YJ
• Hong SI
• Chang YH

• KMID: 1845389
• DOI: http://doi.org/10.3343/lmo.2013.3.1.1

Abstract

BACKGROUND
Autoanalyzer ADVIA2120 uses intracellular peroxidase concentration to perform white blood cell (WBC) differential. Therefore, in specimens containing neutrophils with low peroxidase concentration, neutrophils can be miscounted as monocytes or large unstained cells resulting in pseudoneutropenia. Myeloperoxidase deficiency can be detected by the mean peroxidase index (MPXI). The aims of this study are to establish the reference interval of MPXI and define a cut off value for manual slide review to discriminate pseudoneutropenia.
METHODS
We calculated reference intervals as mean+/-2SD according to the indirect method of CLSI C28-A3 guideline from MPXI data of 5,802 individuals who took routine health checkup from April 2010 to June 2012. We performed manual slide review on specimens with low MPXI and compared neutrophil differential count of manual method with that of autoanalyzer. When neutrophil differential in manual slide review was >20%P higher than autoanalyzer result, it was regarded as a pseudoneutropenia. We performed ROC analysis using the MPXI results of samples with and without pseudoneutropenia to define a cutoff to discriminate pseudoneutropenia.
RESULTS
The reference intervals of MPXI in total population, male, and female were -4.9 to 7.5, -5.5 to 7.3, and -4.5 to 7.5, respectively. The mean value of MPXI was significantly higher in female than in male and there was no difference by age. Twenty-two pseudoneutropenia samples from 7 patients were identified. ROC analysis yielded cutoff value of -20.7 with 94.9% of sensitivity and 77.3% of specificity.
CONCLUSIONS
MPXI may be used in the manual slide review guideline for detecting pseudoneutropenia.

Keyword

Mean peroxidase index; Reference interval; Pseudoneutropenia; Manual slide review

MeSH Terms

Discrimination (Psychology)
Female
Humans
Leukocytes
Male
Metabolism, Inborn Errors
Monocytes
Neutrophils
Peroxidase
ROC Curve
Metabolism, Inborn Errors
Peroxidase

Figure

• 

  Fig. 1 ROC curve evaluating cases with MPO deficiency and low MPXI. The area under the curve (0.894) is shown with its 95% confidence intervals. Abbreviations: MPO, myeloperoxidase; MPXI, mean peroxidase index.

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