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To the Editor.--In their recent paper, Rogers et al (1) highlighted the increased costs that occur when a local laboratory testing system is disrupted and outpatient tests are sent to [...]

Keywords: chloride; measurement uncertainty; metrological traceability; potassium; sodium EN chloride measurement uncertainty metrological traceability potassium sodium e129 e132 4 03/13/21 20210401 NES 210401 To the Editor, Blood electrolyte concentrations are tightly controlled by homeostatic mechanisms, with a very low intraindividual biological variability [[1]]. Importantly, despite the consistent improvement of electrolyte MU, u SB result sb for Na and Cl still exceed APS, while K widely fulfilled them, even at desirable level (i.e., 1.96%), being goals for this ion less stringent due to the relatively higher biological variability in plasma [[1]]. To be clinically useful, measurement results for these analytes should fulfil stringent analytical performance specifications (APS) for their measurement uncertainty (MU), which at minimum should not exceed 0.41% for plasma sodium (Na), 0.74% for plasma chloride (Cl), and 2.94% for plasma potassium (K), in terms of relative standard MU [[1]], [[2]], [[3]], [[4]]. [Extracted from the article]

To be accurate and equivalent, laboratory results should be traceable to higher-order references. Furthermore, their quality should fulfill acceptable measurement uncertainty (MU) as defined to fit the intended clinical use. With this aim, in vitro diagnostics (IVD) manufacturers should define a calibration hierarchy to assign traceable values to their system calibrators. Medical laboratories should know and verify how manufacturers have implemented the traceability of their calibrators and estimate the corresponding MU on clinical samples. Accordingly, the internal quality control (IQC) program should be redesigned to permit IVD traceability surveillance through the verification by medical laboratories that control materials, provided by the manufacturer as a part of measuring systems, are in the clinically suitable validation range (IQC component I). Separately, laboratories should also monitor the reliability of employed IVD measuring systems through the IQC component II, devoted to estimation of MU due to random effects and to obtaining MU of provided results, in order to apply prompt corrective actions if the performance is worsening when compared to appropriate analytical specifications, thus jeopardizing the clinical validity of test results. [ABSTRACT FROM AUTHOR]

Objectives: Procalcitonin (PCT) has been proposed for differentiating viral vs. bacterial infections. In COVID-19, some preliminary results have shown that PCT testing could act as a predictor of bacterial co-infection and be a useful marker for assessment of disease severity. Methods: We studied 83 COVID-19 hospitalized patients in whom PCT was specifically ordered by attending physicians. PCT results were evaluated according to the ability to accurately predict bacterial co-infections and death in comparison with other known biomarkers of infection and with major laboratory predictors of COVID-19 severity. Results: Thirty-three (39.8%) patients suffered an in-hospital bacterial co-infection and 44 (53.0%) patients died. In predicting bacterial co-infection, PCT showed a relatively low accuracy (area under receiver-operating characteristic [ROC] curve [AUC]: 0.757; 95% confidence interval [CI]: 0.651–0.845), with a strength for detecting the outcome not significantly different from that of white blood cell count and C-reactive protein (CRP). In predicting patient death, PCT showed an AUC of 0.815 (CI: 0.714–0.892), not better than those of other more common laboratory tests, such as blood lymphocyte percentage (AUC: 0.874, p=0.19), serum lactate dehydrogenase (AUC: 0.860, p=0.47), blood neutrophil count (AUC: 0.845, p=0.59), and serum albumin (AUC: 0.839, p=0.73). Conclusions: Procalcitonin (PCT) testing, even when appropriately ordered, did not provide a significant added value in COVID-19 patients when compared with more consolidated biomarkers of infection and poor clinical outcome. The major application of PCT in COVID-19 is its ability, associated with a negative predictive value >90%, to exclude a bacterial co-infection when a rule-out cut-off (<0.25 μg/L) is applied. [ABSTRACT FROM AUTHOR]