Gronowski, Ann M.

Abstract Background Serum free light chain (FLC) assays are used clinically to measure the concentration of κ and λ FLC in patients with suspected or diagnosed plasma cell proliferative disorders. Previous studies have demonstrated a loss of linearity in low concentration ranges of these assays. We hypothesized that this result could be caused by a matrix effect. Methods Recovery studies were performed for κ and λ FLC in both serum and saline using the Freelite assay (Binding Site) on a Cobas c502 system (Roche). Samples were analyzed either at the recommended dilution or undiluted. Follow-up studies were performed in varying matrices ranging from 0% to 100% saline. Retrospective patient data were analyzed to assess the impact on reported κ FLC, λ FLC, and κ/λ ratio. Results FLC in a serum matrix demonstrated underrecovery relative to samples diluted in saline for both κ and λ FLC. Of 255 patient samples with λ FLC measured undiluted (λ FLC <6.0 mg/L), an unexpected gap was observed in patient results between 2.0 and 6.0 mg/L. In addition, 23 patients measured serially with λ FLC between 2.0 and 6.0 mg/L demonstrated dramatic changes in κ/λ ratio, with no changes in κ FLC, likely because of the matrix effect. Conclusions The κ and λ Freelite assays exhibit a matrix effect when samples are tested undiluted, which has the potential to affect the κ/λ ratio. Consequently, our laboratory has stopped reporting λ FLC <6.0 mg/L.

Abstract Background Toxoplasmosis is routinely diagnosed through detection of Toxoplasma gondii–specific antibodies. However, the imperfect specificity of T. gondii serologic assays is a well-recognized limitation. The new BioPlex 2200 (Bio-Rad Laboratories) T. gondii, rubella, and cytomegalovirus (ToRC) IgM multiplex flow immunoassay (MFI) received FDA clearance in May 2017. We evaluated the clinical performance of the new T. gondii IgM and existing IgG portion of this MFI. Methods Three hundred prospectively collected consecutive, residual sera, submitted for T. gondii serologic testing as part of routine clinical care, and an archived set of 52 residual sera previously positive for anti–T. gondii IgM and IgG with the predicate ADVIA Centaur Toxoplasma IgM and IgG assays (Siemens) were evaluated. Performance of the BioPlex 2200 T. gondii IgM and IgG MFIs was assessed by calculating positive (PPA) and negative percent agreement (NPA) compared to the Centaur tests. Results Among prospective specimens, the BioPlex 2200 T. gondii IgM and IgG MFIs demonstrated a PPA of 0% (0/7) and 82.3% (28/34) and NPA of 99.3% (288/290) and 95.8% (251/262), respectively, with the Centaur assays. Chart review of the 7 Centaur T. gondii IgM-positive samples revealed that these were likely falsely positive. Among archived samples, the BioPlex 2200 T. gondii IgM and IgG MFIs showed PPAs of 90.4% (47/52) and 100% (52/52), respectively. Conclusions The BioPlex 2200 T. gondii IgM and IgG MFIs demonstrated excellent concordance with the Centaur assays. The T. gondii IgM MFI may provide higher specificity in low-prevalence populations.

Abstract Background Current American College of Gastroenterology (ACG) guidelines suggest that Helicobacter pylori serologic testing may be helpful to rule out H. pylori in areas with low disease prevalence. However, even in low prevalence regions, the positive predictive value of a positive serologic result remains low. Additionally, both the ACG and the American Gastroenterological Association recommend that this noninvasive testing be avoided entirely for patients 55 years and older. Methods The objective of this multicenter retrospective study was to assess H. pylori seroprevalence rates among symptomatic patients and serologic test utilization at the local, state, and national level. Submitted specimens were presumed to be collected from patients with upper gastrointestinal symptoms suspicious for an H. pylori etiology. Results for H. pylori IgG serologic tests performed between 2005 and 2014 were collected from 5 medical centers. Data were evaluated in the context of professional practice guidelines, with a focus on patients ages 55 years and older. Results Nationwide seropositivity among symptomatic individuals is approximately 25%, and 4 of 5 centers reported decreasing seropositivity rates over this 10-year period. State-specific seropositivity among symptomatic patients ranged from 12.4% in the state of Washington to 33.9% in Mississippi. Conclusions We demonstrate that for 48 states >25% of all H. pylori serologic testing was performed in individuals ≥55 years. Despite recommendations to avoid serologic evaluation for H. pylori infection, this study indicates that serology continues to be used at high rates across age-groups.