Journal of Applied Laboratory Medicine最新文献

Background: Arginine vasopressin (AVP) is a neuroendocrine hormone essential for fluid balance, vascular tone, and the endocrine stress response. However, its clinical measurement is limited by instability and technical challenges. Copeptin, the C-terminal segment of the AVP precursor, is secreted in equimolar amounts with AVP and serves as a stable, measurable surrogate.

Content: This mini-review outlines the synthesis, release, and physiological roles of AVP and copeptin, emphasizing their relevance in endocrine regulation. It highlights copeptin's diagnostic utility in differentiating AVP-deficiency (AVP-D), AVP-resistance (AVP-R), and primary polydipsia (PP): conditions that share overlapping clinical features. Traditional diagnostic methods such as the water deprivation test (WDT) are contrasted with copeptin-based approaches, which offer improved accuracy and patient tolerability. The review summarizes diagnostic thresholds for baseline and stimulated copeptin levels using stimulation, such as hypertonic saline or arginine, and discusses their integration into clinical algorithms.

Summary: Copeptin has emerged as a reliable endocrine biomarker for AVP secretion and is increasingly used in the diagnostic evaluation of polyuria-polydipsia syndromes. Its stability, accessibility, and diagnostic performance support its adoption as a first-line tool in endocrine diagnostics.

Background: Methotrexate, an antifolate therapy, is used for the treatment of cancers, autoimmune disease, and transplant patients and needs to be carefully monitored for toxicity. Plasma measurement of methotrexate concentrations is problematic as a result of analytical interference of its metabolites. Immunoassays are widely used for monitoring therapeutic drug levels of methotrexate; however, chromatographic assays, LC-MS/MS most particularly, are preferentially used since they are less prone to metabolite interference.

Methods: Analytical performance was evaluated in a second-generation methotrexate immunoassay (ARK, Inc.) by testing precision, accuracy, linearity, interference, and method comparison with LC-MS/MS. Cross-reactivity of the immunoassay with 4-deoxy-4-amino-N10-methylpteroic acid (DAMPA), 7-OH methotrexate, and folic acid was also measured.

Results: Findings indicate that the within-run %CV ranged from 2.6% to 4.4% across control materials. The assay was linear across an analytical measuring range of 0.03 to 1.3 μM. The lower limit of the measuring interval and the lower limit of detection were established at 0.03 µM and 0.0067 μM, respectively. Notable interference from DAMPA was observed above 1 µM, whereas 7-OH methotrexate and folic acid showed no interference up to 5 µM and 1000 µM, respectively. Correlation studies showed an average 3% bias in DAMPA-free samples (R2 = 0.9935) and a significant bias and poorer correlation (R2 = 0.3241) in samples containing DAMPA.

Conclusions: The assay performed well based on the validation experiments and is suitable for most clinical applications involving methotrexate. However, the significant interference with DAMPA highlights the necessity for careful assay selection and interpretation of glucarpidase-treated patients.

Background: X and Y chromosome analysis is a critical component of genetic testing, used both diagnostically and as a quality control (QC) metric. Discordances between expected and observed sex chromosome data can arise due to mislabeling, demographic data errors, transplant history, or biological variations. Such discordances pose challenges to laboratories and affect patient care, particularly in marginalized populations and unique clinical contexts.

Methods: We reviewed cases of sex chromosome discordance identified at our laboratory from January 2021 through August 2023. Cases spanned various testing methods and were categorized by the root cause, including mislabeling, sample mix-ups, transgender individuals, stem cell transplants, and unexplained causes. Case outcomes were assessed, and potential resolutions were analyzed.

Results: Among 65 cases identified, the leading cause of discordance was mislabeling (n = 20, 31%), followed by other/not identified (n = 16, 25%), sample mix-ups (n = 13, 20%), transgender individuals (n = 9, 14%), and stem cell transplants (n = 7, 11%). Cases required additional QC processes such as reanalysis, clinician contact, and occasionally sample re-collection. The process extended turnaround times by up to 13 business days. Detailed case reviews highlighted the challenges and implications of managing these discordances, emphasizing the importance of accurate data transmission and inclusive practices.

Conclusion: Using X and Y chromosome data as a QC metric can identify critical errors but also introduces limitations and bias. Improved standardization, inclusive practices, and alternative QC methods are necessary to ensure accuracy and equitable patient care. Collaborative efforts are required to address demographic complexities and reduce testing delays.

Background: Accurate and timely identification of upper respiratory tract pathogens can improve patient management by decreasing unnecessary additional testing, reducing the cost of care, and informing antimicrobial stewardship. We evaluated the FDA-cleared Diasorin LIAISON PLEX® Respiratory Flex (RSP Flex), a highly multiplexed, rapid nucleic acid detection assay that can identify 14 viral and 5 bacterial respiratory pathogens.

Methods: In total, 215 residual patient upper respiratory tract specimens were tested using the RSP Flex assay and results compared to standard-of-care (SOC) molecular testing.

Results: Positive percentage agreement (PPA) was 100% for the following targets: adenovirus, human coronavirus, Bordetella pertussis, Bordetella parapertussis, Mycoplasma pneumoniae, and Chlamydia pneumoniae. Performance for the remaining panel targets were: human enterovirus/rhinovirus PPA = 97.5% (39/40), influenza A virus PPA = 92.3% (12/13), human metapneumovirus PPA = 87.5% (14/16), influenza B virus PPA = 92.9% (13/14), parainfluenza 1 virus PPA = 85.7% (6/7), parainfluenza 2 virus PPA = 80% (4/5), parainfluenza 3 virus PPA = 85.7% (12/14), parainfluenza 4 virus PPA = 87.5% (7/8), respiratory syncytial virus (RSV) PPA = 92.9% (13/14), and SARS-CoV-2 PPA = 95.0% (19/20). The negative percentage agreement (NPA) for all targets was 100% except adenovirus NPA = 98.4% (180/183), enterovirus/rhinovirus NPA = 96.9% (155/160), and M. pneumoniae NPA = 91.9% (34/37). For all targets, the RSP Flex assay had an overall PPA of 93.8%, NPA of 99.5% and complete concordance of 99.1% compared to SOC testing.

Conclusions: The LIAISON PLEX RSP Flex assay is a fully automated, sample-to-customizable answer system that offers a wide range of bacterial and viral target testing with high accuracy.

Background: Sigma methodology has become a valuable tool in clinical laboratories for assessing analytical performance and optimizing QC. However, the choice of total allowable error (TEa) sources significantly influences sigma calculation outcomes and can lead to inconsistent quality classifications. In this study, we aimed to evaluate how different TEa guidelines impact sigma metrics and internal quality control (IQC) strategies in order to highlight the need for harmonization in TEa selection.

Methods: A prospective observational study was conducted over 3 months (April-June 2025) in the Clinical Biochemistry Laboratory at Bechir Hamza Children's Hospital. Sigma metrics were calculated for 14 routine analytes at 2 QC levels (level 1 and level 2) using internal and external QC data. Three TEa sources were used: CLIA 2025 (regulatory-based), Randox International Quality Assessment Scheme (RIQAS; peer group-based), and European Federation of Laboratory Medicine (EFLM; biological variation-based). IQC procedures were adapted based on Westgard sigma rules and flowcharts.

Results: Substantial variability in sigma metrics was observed across the 3 TEa guidelines. The same analyte could be classified as "world-class" under EFLM but "unacceptable" under RIQAS. Electrolytes (sodium, potassium, chloride) consistently exhibited poor performance across all guidelines. Visual tools, including radar and sigma charts, confirmed discrepancies. These differences significantly influenced the selection and complexity of IQC procedures.

Conclusions: The choice of TEa guideline exerts a critical influence on sigma metrics and subsequent IQC planning. Current inconsistencies highlight the urgent need for standardized TEa criteria that are both clinically meaningful and practically achievable. Harmonization would improve comparability, optimize laboratory resources, and support evidence-based quality management in clinical laboratories.

Background: Cardiac troponins (cTn) are used as diagnostic biomarkers of acute myocardial infarction (MI), but elevated levels of cTn can also be observed in other conditions. We report here the design and analytical evaluation of an immunoassay that targets intact and mildly fragmented forms of cardiac troponin T (referred to as long cTnT), which has been shown to better differentiate between MI and end-stage renal disease than the current Roche Elecsys® high sensitivity cTnT assay.

Methods: The long cTnT assay was evaluated for analytical characteristics. Serum and heparin plasma sample matrices were compared and the analyte stability was studied by storing endogenous long cTnT from samples of ST-segment elevation MI patients in heparin plasma or buffer at different temperatures and subjecting samples to freeze-thaw cycles. The correlation of long cTnT levels and time after MI symptom onset was also studied.

Results: The long cTnT assay achieved a limit of detection of 10.8 ng/L and a lower limit of quantitation (10% CV) of 30.8 ng/L. The response was linear from 5 to 5000 ng/L. Serum produced significantly lower results than heparin plasma. Endogenous long cTnT tolerated freeze-thaw cycles, but stability was compromised when stored at higher temperatures. The fraction of circulating long cTnT was highest during early hours of MI.

Conclusion: The long cTnT assay presented good analytical performance. Our results support using heparin plasma as the sample material and avoiding prolonged sample storing at room temperatures. Long cTnT fraction decreases in time after the onset of type 1 MI. ClinicalTrials.gov registration: NCT04465591.

Background: Multiplex immunoassays and indirect immunofluorescence assays (IFA) are frequently used for the detection of antineutrophil cytoplasmic antibodies (ANCA) but can produce differing results.

Methods: To understand the settings in which discordant results occur, we retrospectively investigated first-recorded cytoplasmic ANCA (cANCA) IFA and antiproteinase 3 (PR3) results (n = 15 772) generated over 4 years in our clinical laboratory.

Results: We detected significant bidirectional disagreement between cANCA and anti-PR3-antibody results that was not immunoassay or instrument specific. Sixteen percent (22/139) of cANCA-positive specimens were negative for anti-PR3 by multiplex immunoassay. Similarly, 61% (175/285) of anti-PR3 positive specimens were negative for cANCA by IFA. Borderline or indeterminate positivity thresholds could not fully explain the discrepancy between results, suggesting that patient-associated characteristics may contribute. Medical record review of patients with discordant testing over time revealed cANCA/anti-PR3 disagreement in patients with ANCA-associated vasculitis on chronic immunomodulatory therapy, suggesting a treatment-related phenomenon. Among 59% (13/22) of patients for whom serial ANCA testing was evaluated, cANCA semiquantitative titers and anti-PR3 antibody quantitative results trended together and correlated with disease activity in response to immunomodulatory therapy. However, asynchronous changes were observed in 41% (9/22) of patients, leading to significant differences in anti-PR3 or cANCA results despite sustained cANCA or anti-PR3 antibody negativity, respectively.

Conclusion: In certain individuals, anti-PR3 antibodies and cANCA titers may differentially capture disease activity, and cANCA/anti-PR3-discordant results may have clinical significance in the setting of immunomodulatory therapy. Our data argue for a complementary testing approach that implements both immunoassay and IFA methods to detect these changes over time.

Background: Hereditary myopathies are a heterogeneous group of genetic disorders affecting skeletal muscle. The molecular diagnosis of these conditions has been revolutionized by next-generation sequencing (NGS), significantly improving diagnostic accuracy. This study aimed to characterize the genetic causes of primary myopathies in a cohort of Colombian male patients.

Methods: A total of 175 male individuals with clinical suspicion of hereditary myopathy were evaluated. Multiplex ligation-dependent probe amplification (MLPA) was performed to detect deletions/duplications in the DMD gene, and targeted NGS panel sequencing was applied in MLPA-negative cases and those with single-exon deletions.

Results: MLPA identified DMD deletions or duplications in 44.6% (78/175) of patients, confirming Duchenne/Becker muscular dystrophy (DBMD). NGS was performed in 97 patients, revealing pathogenic or likely pathogenic variants in 30.4% (17/56) of the analyzed genes. The overall diagnostic yield of the combined MLPA and NGS strategy was 85.7% (150/175). DBMD was the most frequent diagnosis (74.3%; 130/175), followed by limb-girdle muscular dystrophies (5.7%; 10/175). NGS also identified 38 variants of uncertain significance (VUS) in 43.3% (42/97) of analyzed samples.

Conclusions: The combined use of MLPA and targeted NGS improves the molecular diagnosis of hereditary myopathies. This approach provides insights into the genetic landscape of neuromuscular disorders, enabling better clinical management, genetic counseling, and potential eligibility for emerging therapies.