Evaluation of Performance and False Positivity of Mediace RPR Test that Uses a Chemistry Autoanalyzer / 대한진단검사의학회지

BACKGROUND: We evaluated the performance and false positive rate of Mediace RPR test (Sekisui, Japan), a newly introduced nontreponemal test using a chemistry autoanalyzer. METHODS: The sensitivity of Mediace RPR test was analyzed using sera from 50 patients with syphilis in different stages (8 primary, 7 secondary, and 35 latent), 14 sera positive with fluorescent treponemal antibody absorption (FTA-ABS) IgM, and 74 sera positive with conventional rapid plasma regain (RPR) card test (Asan, Korea) and also positive with Treponema pallidum hemagglutination (TPHA) test or FTA-ABS IgG test. The specificity was analyzed on 108 healthy blood donors. We also performed RPR card test on 302 sera that had been tested positive with Mediace RPR test and also performed TPHA or FTA-ABS IgG test to analyze the false positive rate of Mediace RPR test. A cutoff value of 0.5 R.U. (RPR unit) was used for Mediace RPR test. RESULTS: Mediace RPR test on syphilitic sera of different stages (primary, secondary, and latent stages) and FTA-ABS IgM positive sera showed a sensitivity of 100%, 100%, 82.9% and 100%, respectively. Among the 74 sera positive with conventional RPR card test and TPHA or FTA-ABS IgG test, 55 were positive with Mediace test. The specificity of Mediace RPR test on blood donors was 97.2%. Among the 302 sera positive with Mediace RPR test, 137 sera (45.4%) were negative by RPR card and TPHA/FTA-ABS IgG tests. CONCLUSIONS: Although the sensitivities of Mediace RPR were good for primary and secondary syphilis, due to its high negative rate of Mediace RPR over the conventional RPR positive samples, further studies are necessary whether it can replace conventional nontreponemal test for screening purpose. Moreover, in view of the high false positive rate, positive results by Mediace RPR test should be confirmed with treponemal tests.

The Measurement of Red Cell Size in Peripheral Blood Smear:Comparison of Mean Corpuscular Area and Mean Corpuscular Volume / 대한임상병리학회지

BACKGROUND: We intended to investigate the relationship between red cell size observed through a light microscope and mean corpuscular volume (MCV) measured by an automatic hematology analyzer. METHODS: 164 samples which were referred for complete blood count analysis and peripheral blood cell morphology were selected. MCV was measured by Gen-S (Coulter Co., USA). Smear slides of the same samples were examined on a microscope with a CCD camera connected to it. The image observed through the microscope emerged on an IBM-compatible computer system through the CCD camera. Mean red cell size-mean corpuscular area (MCA) of the captured image was calculated by Image-Pro Plus, the image capture and analyzing software. RESULTS: The coefficient of variation (CV) of MCA measurement, which was done 5 times on 10 slides, was 1.5-3.6%. Compared to the measurements performed in the ideal zone, MCA was measured lower in the thickly smeared zone (medial zone) and higher in the thinly smeared zone (lateral zone) on smear slide observation. The correlation between MCA and MCV values was poor (R=0.641, P<0.01). The normal reference range of MCA measurement was 37.40-50.22 m2. CONCLUSIONS: As the red cell size observed on the light microscope does not correlate well with the MCV measured by automatic analyzer, the determination of red cell size by microscopic peripheral blood smear requires profound caution.