Evaluation of an automated capillary electrophoresis system in the screening for hemoglobinopathies.

BACKGROUND: The biochemical diagnosis of hemoglobinopathies (thalassemias and hemoglobin (Hb) variants) is based on the separation and the quantification of Hb fractions. HPLC is the most commonly used method but capillary electrophoresis (CE) methods have also been developed successfully. The Capillarys II system is the first fully automated CE system that allows the quantification of Hb A2 and Hb F and the separation of Hb variants. We evaluated the ability of this system to separate and identify Hb variants and to quantify Hb A2 and Hb F. MATERIAL AND METHODS: The separation of 18 different Hb variants was studied and the imprecision on migration times was calculated for the three most frequent ones. The total imprecision on Hb A2 and Hb F quantification was determined. The results obtained for 44 patients were compared with those given by HPLC. The interference on Hb A2 measurement due to the presence of Hb S was studied. RESULTS: Fourteen out of the 18 variants tested, including all variants of clinical importance, were separated from Hb A. Imprecision on migration times was less than 1%. For Hb A2 quantification, imprecision was less than 3.5% and for Hb F, less than 7.0%. The comparison with HPLC showed an acceptable agreement between both methods but a systematic negative bias for Hb A2 and both proportional and systematic biases for Hb F. No interference from the presence of Hb S on the quantification of Hb A2 was observed. CONCLUSIONS: The fully automated Capillarys Hemoglobin method allows the detection and the separation of the most common Hb variants. It provides also a precise, quick, and very easy quantification of Hb F and Hb A2, even in the presence of Hb S. It is very suitable for routine investigation of hemoglopinopathies.

Evaluation of disc diffusion methods and Vitek 2 automated system for testing susceptibility to mupirocin in Staphylococcus aureus.

OBJECTIVES: To compare the performance of the automated Vitek 2 system, the disc diffusion method and a home-made mupirocin screen agar (MSA) to detect mupirocin resistance in methicillin-resistant Staphylococcus aureus (MRSA) isolates. METHODS: A total of 125 MRSA isolates were tested. The level of mupirocin resistance was determined by agar dilution and Etest techniques (gold standard), by the Vitek 2 system, on MSA (Mueller-Hinton + mupirocin 4 mg/L) and with the disc diffusion method using 10 microg mupirocin Neo-Sensitabs (MUP-10) and mupirocin paper discs of 5, 20 and 200 microg (MUP-5, MUP-20 and MUP-200). High-level mupirocin resistance (HLMR) was confirmed by PCR for the mupA gene. RESULTS: Thirty-two MRSA isolates showed HLMR (MIC > or = 512 mg/L) and harboured the mupA gene, 39 strains showed low-level mupirocin resistance (LLMR) (8-32 mg/L) without the mupA gene and 54 were susceptible without the mupA gene. The sensitivity and the specificity of the Vitek 2 system and the screening medium (MSA) for the detection of mupirocin resistance was 100%. The diffusion method using 5 and 10 microg discs demonstrated a sensitivity of 100% and a specificity of 98.1% and 100%, respectively. Using interpretative criteria of 6 and 17 mm, the MUP-20 disc showed the best classification concordance with reference methods. CONCLUSIONS: The diffusion method using low-content discs or the Vitek 2 microdilution system showed excellent agreement with MICs and PCR results to separate mupirocin-susceptible from -resistant MRSA strains. Disc diffusion with MUP-20 or combined use of low and high mupirocin content discs enabled the classification of susceptibility categories (susceptible, LLMR and HLMR) but required overnight incubation compared with 12 h for the Vitek 2 system.