Diagnostic performance of the ARCHITECT C-Peptide immunoassay.

BACKGROUND: Measurement of C-peptide under standardized conditions provides a sensitive and well-established assessment of beta-cell function. We describe the analytical and clinical validation of an automated, microparticle-based chemiluminescent immunoassay method. The assay is designed to measure C-peptide in human serum, plasma and urine. METHODS: Assay performance characteristics such as precision and recovery were measured according to protocols established by the Clinical Laboratory Standards Institute (CLSI). A reference range study was conducted. Analytical sensitivity and specificity, interfering substances, recovery, and linearity studies were performed. Method comparison, against the ADVIA Centaur C-Peptide assay (Siemens), was evaluated with clinical specimens from patients with abnormal insulin secretion. RESULTS: The detection limit for this assay was 0.01 ng/mL. Functional sensitivity (inter-assay imprecision < or = 20%) was 0.015 ng/mL at a coefficient of variation (%CV) of 11.2%. Total imprecision was below 6.5% CV. The assay was linear upon dilution. Comparison with the ADVIA Centaur C-Peptide assay yielded a correlation coefficient (r) of 0.99. CONCLUSIONS: The ARCHITECT C-Peptide assay measures C-peptide rapidly, accurately, and precisely in human serum, plasma and urine. It provides useful improvements for beta-cell function testing and for evaluating the clinical status of a patient in combination with other diabetes markers.

The Lim-only protein LMO2 acts as a positive regulator of erythroid differentiation.

LMO2, a member of the LIM-only protein family, is essential for the regulation of hematopoietic stem cells and formation of erythroid cells. It is found in a transcriptional complex comprising LMO2, TAL1, E47, GATA-1, and LDB1 which regulates erythroid genes. While TAL1 has been shown to induce erythroid differentiation, LMO2 appears to suppress fetal erythropoiesis. In addition to LMO2, the closely related LMO4 gene is expressed in hematopoietic cells, but has unknown functions. Here we demonstrate that LMO2 and LMO4 are expressed at the same level in erythroid colonies from mouse bone marrow, implying a function in erythroid differentiation. However, while LMO2 induced erythroid differentiation, LMO4 had no such effect. Interestingly, both LMO2 and TAL1 were able to partially suppress myeloid differentiation, implying that they activate erythroid differentiation in uncommitted bone marrow progenitors. Both LMO2 and LMO4 interacted strongly to LDB1, which was required for their localization to the nucleus.