Vertical cutoff methods in serum protein electrophoresis for the measurement of monoclonal protein concentrations: Which is best?

BACKGROUND: Monoclonal protein (M-protein) concentrations are measured by serum protein electrophoresis (SPE). Two methods are used for demarcating the M-protein area in the electropherogram: perpendicular drop (PD) and tangent skimming (TS). The aim of this study was tocompare both methods and to establish which is the most accurate and precise. METHODS: We studied 24 sera containing M-protein (5-44 g/L). The systematic error (SE) was evaluated in a dilution series of 12 sera. Within-day, between-day, and interobserver variability were assessed. SPE was performed by capillary and agarose gel electrophoresis. M-protein concentrations were measured using both cutoff methods. RESULTS: The PD method shows a constant SE ranged 1.00-2.27 g/L, while constant SE for TS is ranged -0.30--0.57 g/L. None of the cutoff methods or electrophoretic methods showed a proportional SE, with the exception of the TS method in capillary electrophoresis for ß-migrating M-protein. The PD method was more precise than the TS method in all three estimates of imprecision. An increased CV for concentrations < 10 g/L in between-day imprecision was observed with the TS method. Interobserver imprecision was greater for M-protein concentrations < 17 g/L for both cutoff methods (14.85%, 26.42% respectively). CONCLUSIONS: Despite being less precise, the TS method provides a more accurate measurement of M-protein concentration.

[A Staphylococcus haemolyticus study in urinary infections. An analysis of 8 cases]. / Estudio de Staphylococcus haemolyticus en las infecciones urinarias. Análisis de ocho casos.

Urinary infections caused by Staphylococcus are attributed usually to Staphylococcus epidermidis or Staphylococcus saprophyticus. 8 cases of urinary infection due to S. haemolyticus are discussed: 5 adults all of them over 66 years, diagnosed respectively of diabetes, cancer and stroke. Three children diagnosed of febrile syndrome, encephalopathy and enterocolitis associated with urinary infection. S. haemolyticus was identified through the determination of 19 biochemical parameters. The antibiograms performed showed that all S. haemolyticus isolated were sensible to vancomycin, nitrofurantoin and trimethoprim/sulfamethoxazole. It is concluded that S. haemolyticus is an opportunistic pathogen that is present on immunodepressed hosts, that is why is advisable to perform a more in-depth characterization of the S. epidermidis isolated in urine, especially in persistent pathologic processes.