Evaluation of the N-latex serum free light chain assay on the Siemens BNII analyzer and agreement with The Binding Site FreeLite assay on the SPAPlus.

OBJECTIVES: To evaluate the Siemens N-latex kappa free light chain (κFLC) and lambda FLC (λFLC) assays on the BNII nephelometer and assess agreement with The Binding Site Freelite FLC assays on the SPAPlus. DESIGN AND METHODS: Over 180 patient serum samples from routine analysis of κFLC and λFLC measured by the Freelite assay were collected for the study and measured with the N-latex κFLC and λFLC assays to assess precision, linearity, method comparison and dilutional effects. RESULTS: Complex precision showed coefficients of variation of 4.8-7.2% for the κFLC assay and 3.6-6.0% for the λFLC assay. Linearity assessment showed both assays were linear (κFLC, y=1.00x-0.09 and λFLC, y=1.050x-1.252). Qualitative method comparison showed 87.9% (116/132) agreement and Cohen's kappa of 80.4% between the κFLC assays and 72.6% (98/135) agreement and Cohen's kappa of 55.4% for the λFLC assays. Quantitative method comparison for κFLC<150mg/L was y=0.92x+2.21, R=0.661 and for λFLC<150mg/L was y=7.90x-137.96, R=0.526. Dilutional effects including antigen excess and non-linearity were also examined. CONCLUSIONS: The N-latex assay showed good precision and linearity with reasonable agreement to the Freelite assay. However, the assays should not be used interchangeably to monitor patients.

Comparative evaluation of three FDA-approved HIV Ag/Ab combination tests using a genetically diverse HIV panel and diagnostic specimens.

BACKGROUND: HIV Ag/Ab combination assays are recommended by CDC for routine screening and several HIV Ag/Ab combination tests are now FDA-approved. Maintaining high specificity and consistent sensitivity across diverse HIV strains is critical for these assays to accurately detect HIV infection and expedite delivery of patient results. OBJECTIVES: To evaluate performance of three FDA-approved HIV tests: ARCHITECT HIV Combo (Abbott), ADVIA Centaur HIV Combo (Siemens) and BioPlex HIV Ag-Ab (Bio-Rad). STUDY DESIGN: Sensitivity and specificity were evaluated using an extensive panel of 28 HIV infected human specimens and 17 cultured virus isolates representing multiple genotypes, 6 seroconversion panels, 4 human samples with acute infection, WHO p24 standard and 4020 clinical specimens. RESULTS: The p24 limit of detection (LOD) for the WHO standard was 0.19IU/ml, 0.70IU/ml, and 1.77IU/ml in BioPlex, ARCHITECT, and Centaur respectively. The distribution of LODs across 15 HIV-1 isolates was substantially narrower in ARCHITECT (5-33pg/ml) than in BioPlex (11-198pg/ml) and Centaur (6-384pg/ml). All assays detected antibodies to the majority of HIV-1 and HIV-2 variants. However, reduced sensitivity was observed for Centaur in detection of antibodies to HIV-1 group M (CRF02_AG), O and N variants. BioPlex and ARCHITECT showed better seroconversion sensitivity than Centaur, detecting one bleed (3-7 days) earlier in 4 (BioPlex) and 3 (ARCHITECT) of 6 seroconversion panels. ARCHITECT demonstrated the highest specificity (99.90-100%) compared to BioPlex (99.80%) and Centaur (99.42%). CONCLUSIONS: The overall performance of ARCHITECT and BioPlex was superior to Centaur, especially for detection of acute HIV infection.

Analytical evaluation of the BioPlex® 2200 25-OH vitamin D total assay.

BACKGROUND: Testing for 25-hydroxyvitamin D (25(OH)D) has increased dramatically over the past decade and several automated immunoassays exist to measure serum 25(OH)D. Here we assess the performance of the recently released automated Bio-Rad BioPlex® 2200 25-OH vitamin D immunoassay, claimed to equally detect 25(OH)D2 and 25(OH)D3, and compare its results against a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method and the well-established DiaSorin LIAISON® 25-OH vitamin D total immunoassay. METHODS: Imprecision was determined using third party controls over 20days. Linearity over the claimed measuring range was assessed using admixtures of a high and a low patient pool. Correlation between the BioPlex and LC-MS/MS (n=137) or the LIAISON (n=56) was assessed using patient samples with varying amounts of 25(OH)D3 and/or 25(OH)D2. RESULTS: The total imprecision was 9.4%, 6.9% and 4.5% at concentrations of 39.4nmol/L, 70.6nmol/L and 242.8nmol/L, respectively. The assay was linear from 33.1-375.0nmol/L with a R(2) of 0.993. Method comparison revealed a strong correlation between the BioPlex assay and LC-MS/MS for samples containing 25(OH)D2 alone (n=5; R(2)=0.999), 25(OH)D3 alone (n=119; R(2)=0.935) and both (n=13; R(2)=0.919). In samples tested by all three methods (n=56), the correlation between the BioPlex and the LIAISON (R(2)=0.853) was poorer than that of the BioPlex and LC-MS/MS (R(2)=0.942). CONCLUSION: The BioPlex assay is suitable for the measurement of total serum 25(OH)D. The strong correlation between the BioPlex assay and LC-MS/MS in detecting 25(OH)D2 and 25(OH)D3 provides evidence that the BioPlex assay is capable of the equivalent detection of both forms.

Elastic behaviour of a nanocomposite thin film undergoing significant strains.

For nearly a century, dielectric materials have been used to produce thin film filters capable of precisely modifying electromagnetic wave interactions at material boundaries. Minimizing visible reflections from optical elements is the most mature use of these techniques, but modern applications often require advanced filters that operate in the ultraviolet or infrared regions. Vapour deposition is the dominant coating technology used to produce these filters, but sol-gel processes have also gained a footing. These methods have been used to create organic/inorganic hybrids that can theoretically withstand larger strains than a purely inorganic metal oxide, but demonstrations of thin film filters with strain properties similar to pure polymers have been sorely lacking. A homogeneous composite featuring inorganic nanoparticles in a polymer matrix is capable of very high strains without failure. We demonstrate such a system here with a 38-layer nanocomposite filter that is subjected to 20% strain with simultaneous evaluation of optical performance. The filter's reflectance peak shifts toward the shorter wavelengths as film thickness decreases in response to the strain, but the peak intensity of the reflected light does not substantially change. These results suggest that the nanocomposite layers are behaving as homogeneous materials with consistent optical parameters throughout the test.

Are benzodiazepines still the medication of choice for patients with panic disorder with or without agoraphobia?

OBJECTIVE: Recently, pharmacological treatment guidelines for panic disorder have changed as newer treatment options have become available. The authors examined how the use of psychotropic drugs has shifted over the course of 10 years to determine if prescribing patterns have changed to reflect these revised treatment guidelines. METHOD: A total of 443 patients with panic disorder were enrolled in the Harvard/Brown Anxiety Research Project, a prospective longitudinal study of anxiety disorders. These patients were interviewed over the course of 10 years to examine their use of psychotropic medications. RESULTS: Despite efforts aimed at increasing the use of selective serotonin reuptake inhibitors (SSRIs) in patients with panic disorder (e.g., APA's practice guideline for panic disorder, Food and Drug Administration approval of particular SSRIs for the treatment of panic disorder), only a modest increase in their use was found. Treatment patterns for psychotropic drugs appear to have remained stable over the past decade, with benzodiazepines being the most commonly used medication for panic disorder. In comparison, SSRI use throughout the follow-up period has remained low. Patients using an SSRI did not have a more favorable clinical course than those using a benzodiazepine, nor were there significantly better rates of remission in patients using SSRIs and benzodiazepines concomitantly. CONCLUSIONS: These results highlight a gap between pharmacological treatment guidelines and actual delivery of care in that recommendations to use SSRIs to treat panic disorder are not being followed. Factors potentially associated with promoting and ignoring treatment recommendations are discussed.