Kim B, et al. J Korean Med Sci. 2023 Mar;38(14):e101. https://doi.org/10.3346/jkms.2023.38.e101

Vitamin D (vit-D) deficiency is highly prevalent in the Korean population, highlighting the need for accurate measurements. In this study, the interferences by endogenous and cross-reactive substances were compared between routine vit-D immunoassays and mass spectrometry (MS) methods. Two MS methods and 4 immunoassays from different manufacturers (Abbott, Beckman Coulter, Roche, Siemens) were compared. Residual samples that were icteric, lipemic, hemolyzed, high in rheumatoid factor, from myeloma patients, or patients undergoing hemodialysis were collected. Also, 4 levels of National Institute of Standards and Technology (NIST) Standard Reference Material 972a, and 12 samples serially spiked with 3-epi-25-OH-D₃ were prepared. Significant interferences were observed in hemolytic (Roche), icteric (Beckman and Siemens) and lipemic samples (all 4 immunoassays). Level 4 NIST material and 3-epi-25-OH-D₃-spiked samples induced significant cross-reactivity, yielding higher total vit-D measurements in non-epimer-separating MS methods, and both the Beckman and Roche immunoassays. Most observed interferences were consistent with manufacturers’ claims, but overall improvement of immunoassay bias limits is required. Awareness of potential interference is important to increase the accuracy of vit-D measurements. Moreover, care is due when interpreting vit-D results of newborns, infants and less commonly, pregnant women, who are known to have physiologically high levels of the highly cross-reactive 3-epi-25-OH-D₃.

Youngwon Nam, M.D., Joon Hee Lee, M.D., Sung Min Kim, M.T., Sun-Hee Jun, M.T., Sang Hoon Song, M.D., Ph.D., Kyunghoon Lee, M.D., and Junghan Song, M.D., Ph.D.. Ann Lab Med 2022;42:150-9. https://doi.org/10.3343/alm.2022.42.2.150

Background: Detecting monoclonal protein (M-protein), a hallmark of plasma cell disorders, traditionally relies on methods such as protein electrophoresis, immune-electrophosuch as matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and electrospray ionization-quadrupole time-of-flight (ESI-qTOF) MS, have emerged as sensitive methods. We explored the M-protein-detection efficacies of different MS techniques. Methods: To isolate immunoglobulin and light chain proteins, six types of beads (IgG, IgA, IgM, kappa, lambda, and mixed kappa and lambda) were used to prepare samples along with CaptureSelect nanobody affinity beads (NBs). After purification, both MALDI-TOF MS and liquid chromatography coupled with Synapt G2 ESI-qTOF high-resolution MS analysis were performed. We purified 25 normal and 25 abnormal IFE samples using NBs and Results: Abnormal samples showed monoclonal peaks, whereas normal samples showed polyclonal peaks. The IgG and mixed kappa and lambda beads showed monoclonal peaks following the use of daratumumab (an IgG/kappa type of monoclonal antibody) with both MALDI-TOF and ESI-qTOF MS analysis. The limits of detection for MALDI-TOF MS and ESIqTOF MS were established as 0.1 g/dL and 0.025 g/dL, respectively. Conclusions: NB-MALDI-TOF and IFE exhibited comparable sensitivity and specificity (92% and 92%, respectively). identified monoclonal peaks with both MALDI-TOF and ESI-qTOF analyses. Qualitative analysis using MALDI-TOF yielded results comparable with that of IFE. NB-MALDI-TOF might be used as an alternative method to replace conventional tests (such as IFE) to detect M-pro

Background: Hemoglobin A_1c (HbA_1c) is arguably the most important biomarker used in the diagnosis and treatment monitoring of diabetes mellitus. We evaluated the analytical performance of the Norudia HbA_1c assay (Sekisui Medical Co., LTD), which uses an enzymatic method incorporated into a fully automated, high‐throughput system.Methods: The precision, linearity, and carryover of the Norudia HbA_1c assay were evaluated. Using 60 patient samples, comparative analysis of HbA_1c measurements with two commonly used HbA_1c assays, the D100 (Bio‐Rad Laboratories, Inc) and HLC‐723 G11 (Tosoh), was undergone. Thirteen commutable samples with known HbA_1c concentrations measured using an IFCC reference measurement procedure were used to compare accuracy between methods. Interference of HbA_1c measurement by Hb variants was evaluated using 16 known Hb variant samples.Results: Repeatability (% CV) for low and high concentrations ranged from 1.12%‐1.50% and 0.66%‐0.75%, respectively, and within‐laboratory precision for low and high concentrations ranged from 1.73%‐2.89% and 0.98%‐1.64%, respectively. For linearity, the coefficient of determination was 0.9987. No significant carryover was observed. When compared to the D100 and HLC‐723 G11 assays, the Norudia HbA_1c assay showed the best accuracy with the lowest mean bias (−1.72%). Furthermore, the Norudia was least affected by Hb variants and gave the most reliable HbA_1c measurements.Conclusion: The Norudia HbA_1c showed excellent analytical performance with good precision and linearity, and minimal carryover. When compared to other routine HbA_1c methods, the Norudia HbA_1c assay showed the highest accuracy and was least affected by Hb variants.

Background: Vancomycin therapeutic drug monitoring (TDM) is essential for optimizing efficacy and minimizing toxicity, particularly in acute kidney injury (AKI). However, recent guidelines favor area under the curve (AUC)-guided dosing over traditional trough monitoring to improve dosing. This study aimed to compare vancomycin TDM strategies in pediatric patients, examine the agreement between 1-point and 2-point sampling methods for AUC estimation, and explore the association between vancomycin exposure and clinical outcomes. Methods: This retrospective cohort study included pediatric patients (2 months to 18 years of age) who underwent vancomycin TDM between 2017 and 2019 (trough-based dosing) and 2020 and 2022 (AUC-based dosing). The pharmacokinetic parameters were estimated using Bayesian software. AKI was defined according to the Kidney Disease: Improving Global Outcomes criteria. Receiver operating characteristic curve analysis was performed to identify the threshold values of AUC and trough concentrations for predicting AKI. Results: A total of 288 patients were included in the study: 164 were from 2017 to 2019 and 124 were from 2020 to 2022, respectively. A comparison of the 1-point and 2-point sampling methods for estimating the AUC showed no significant differences. The incidence of AKI was slightly lower in the 2020–2022 cohort (2.4%) than in the 2017–2019 cohort (6.7%), though the difference was not statistically significant. The AUC threshold for predicting AKI was similar between 1-point and 2-point sampling methods (588–621 mg h/L). Conclusions: AUC-based vancomycin dosing was associated with a reduced incidence of AKI in pediatric patients, without compromising efficacy. Further studies are warranted to refine the exposure targets for bacteremia resolution.