Improving the diagnosis of active tuberculosis: a novel approach using magnetic particle-based chemiluminescence LAM assay.

OBJECTIVES: Tuberculosis (TB) is a significant global health concern, given its high rates of morbidity and mortality. The diagnosis using urine lipoarabinomannan (LAM) primarily benefits HIV co-infected TB patients with low CD4 counts. The focus of this study was to develop an ultra-sensitive LAM assay intended for diagnosing tuberculosis across a wider spectrum of TB patients. DESIGN & METHODS: To heighten the sensitivity of the LAM assay, we employed high-affinity rabbit monoclonal antibodies and selected a highly sensitive chemiluminescence LAM assay (CLIA-LAM) for development. The clinical diagnostic criteria for active TB (ATB) were used as a control. A two-step sample collection process was implemented, with the cutoff determined initially through a ROC curve. Subsequently, additional clinical samples were utilized for the validation of the assay. RESULTS: In the assay validation phase, a total of 87 confirmed active TB patients, 19 latent TB infection (LTBI) patients, and 104 healthy control samples were included. Applying a cutoff of 1.043 (pg/mL), the CLIA-LAM assay demonstrated a sensitivity of 55.2% [95%CI (44.13%~65.85%)], and a specificity of 100% [95%CI (96.52%~100.00%)], validated against clinical diagnostic results using the Mann-Whitney U test. Among 11 hematogenous disseminated TB patients, the positive rate was 81.8%. Importantly, the CLIA-LAM assay consistently yielded negative results in the 19 LTBI patients. CONCLUSION: Overall, the combination of high-affinity antibodies and the CLIA method significantly improved the sensitivity and specificity of the LAM assay. It can be used for the diagnosis of active TB, particularly hematogenous disseminated TB.

A new pattern of citrullinated peptides improves the sensitivity for diagnosing rheumatoid arthritis.

OBJECTIVES: Anti-citrullinated protein antibody (ACPA) is found almost exclusively in patients with rheumatoid arthritis (RA). Commercial cyclic citrullinated peptide (CCP) assays that target ACPAs yield specificities as high as 95% for RA diagnoses, but their sensitivities only reach 50-70%. To improve the sensitivity of the CCP assay, a new pattern of citrullinated peptide was identified and named the MCSM (multiple citrulline-similar motif). DESIGN & METHODS: The MCSM comprised a citrulline core surrounded by citrulline-similar amino acids. A series of peptides with or without the MCSM was synthesized to evaluate the function of the citrulline core and citrulline-similar amino acids. These peptides were used in the enzyme-linked immunosorbent assay to compare samples from 94 RA patients, 117 non-RA patients and 116 healthy subjects. Additionally, the MCSM assay was compared with a commercial CCP assay. RESULTS: When the cutoff value was set at 0.274, the sensitivity and specificity of the MCSM assay were 79.6% and 96.6%, respectively. When one citrulline was substituted in the citrulline core, the sensitivity of the assay decreased from 79.6% to 61%. If all three citrulline-similar amino acids were substituted in the backbone, the sensitivity of the MCSM assay decreased from 79.6% to 58.5%. The coincidence rate of the MCSM assay to the commercial CCP assay was 97.6%. CONCLUSIONS: The citrulline core and citrulline-similar amino acids are crucial components of the MCSM pattern. This new MCSM assay could be used to diagnose RA.