Establishing metrological traceability for small molecule measurands in laboratory medicine.

For molecules that can be well described metrologically in the sense of the definition of measurands, and which can also be recorded analytically as individual substances, reference measurement service traceability to a metrologically sound foundation is a necessity. The establishment of traceability chains must be initiated by National Metrology Institutes (NMIs) according to applicable standards; they are at the top and leading position in this concept. If NMIs are not in the position to take up this task, alternative approaches must be sought. Traceability initiatives established by in vitro device industry or academia must meet the quality standards of NMIs. Adherence to International Organization for Standardization (ISO) procedure 15193 must be a matter of course for the establishment of reference measurement procedures (RMPs). Certified reference material (CRM) characterization must be thorough, e.g., by the application of quantitative nuclear magnetic resonance measurements and by adherence to ISO 15194. Both for RMPs and CRMs Joint Committee for Traceability in Laboratory Medicine (JCTLM) listing must be the ultimate goal. Results must be shared in a transparent manner to allow other stakeholders including NMIs to reproduce and disseminate the reference measurement procedures.

Quantification of Antibiotics in Patient Samples: State of the Art in Standardization and Proficiency Testing.

BACKGROUND: For many antibiotics, the convenient one-fits-all dosing regimen had to be abandoned. Owing to highly variable pharmacokinetics, therapeutic drug monitoring has become an indispensable prerequisite. It is based on a suitable measuring method, sample materials, and standardization. Appropriate quality control including external quality assessment (EQA) is essential. For many antibiotics, EQAs have been established for many decades, whereas others have only lately been introduced. This article gives an insight into the state of the art regarding the therapeutic drug monitoring of antibiotics regarding standardization, EQAs, and reference measurement procedures (RMPs). METHODS: An overview of the currently available international EQA schemes for antibiotics and a literature overview of available RMPs are given. EQAs including gentamicin and vancomycin have been offered by German providers for more than 25 years. The period 2000-2020 was selected for a detailed analysis. The experiences with a new EQA including linezolid, meropenem, and piperacillin are described. RESULTS: EQAs for gentamicin and vancomycin are provided in many countries. Those for linezolid, meropenem, and piperacillin do not seem to be very common. Most of the antibiotics monitored for decades are measured by commercially available assays. EQAs for linezolid, meropenem, and piperacillin introduced in 2018 were rapidly accepted in Germany. Methods reported in this study were HPLC based either with UV or mass spectrometric detection. The number of participants succeeding was comparable between UV and mass spectrometry. Candidate RMPs for gentamicin, vancomycin, and linezolid based on isotope dilution mass spectrometry were published. CONCLUSIONS: EQAs are offered regularly for many antibiotics worldwide. The results of EQAs in Germany generally compare well, but there is potential for improvement. Both immunoassays and HPLC-based methods work properly in EQAs evaluated in Germany. From a quality control perspective, fast and inexpensive methods may be selected without endangering the patient's health based on clinical needs.

Harmonization status of procalcitonin measurements: what do comparison studies and EQA schemes tell us?

Sepsis represents a global health priority because of its high mortality and morbidity. The key to improving prognosis remains an early diagnosis to initiate appropriate antibiotic treatment. Procalcitonin (PCT) is a recognized biomarker for the early indication of bacterial infections and a valuable tool to guide and individualize antibiotic treatment. To meet the increasing demand for PCT testing, numerous PCT immunoassays have been developed and commercialized, but results have been questioned. Many comparison studies have been carried out to evaluate analytical performance and comparability of results provided by the different commercially available immunoassays for PCT, but results are conflicting. External Quality Assessment Schemes (EQAS) for PCT constitute another way to evaluate results comparability. However, when making this comparison, it must be taken into account that the variety of EQA materials consist of different matrices, the commutability of which has not yet been investigated. The present study gathers results from all published comparison studies and results from 137 EQAS surveys to describe the current state-of-the-art harmonization of PCT results. Comparison studies globally highlight a significant variability of measurement results that nonetheless seem to have a moderate impact on medical decision-making. For their part, EQAS for PCT provides highly discrepant estimates of the interlaboratory CV. Due to differences in commutability of the EQA materials, the results from different peer groups could not be compared. To improve the informative value of the EQA data, the existing limitations such as non-harmonized conditions and suboptimal and/or unknown commutability of the EQA materials have to be overcome. The study highlights the need for commutable reference materials that could be used to properly evaluate result comparability and possibly standardize calibration, if necessary. Such an initiative would further improve the safe use of PCT in clinical routine.

Application of a point of care creatinine device for trend monitoring in kidney transplant patients: fit for purpose?

BACKGROUND: The StatSensor® Xpress-i™, a point-of-care system for blood creatinine measurement, offers patients the possibility of self-monitoring creatinine. In this study, the analytical performance of the StatSensor® for both detecting current renal function and monitoring renal (dys)function in kidney transplant patients was examined. METHODS: Accuracy of the StatSensor® with capillary and venous whole blood was evaluated and compared to an isotopic dilution mass spectrometry (IDMS)-traceable enzymatic creatinine test in venous serum (n=138). Twenty Li-heparin samples were compared to the IDMS reference method performed by a Joint Committee for Traceability in Laboratory Medicine (JCTLM)-listed reference laboratory (RfB, Bonn, Germany). To evaluate StatSensor®'s suitability to monitor kidney function, both venous and capillary samples were obtained in 20 hospitalized transplantation patients. Venous samples were analyzed with an IDMS-traceable enzymatic test, capillary samples were measured using the StatSensor®. For all 2-day intervals, percentage change in creatinine was compared between both methods. RESULTS: The StatSensor® did not meet total allowable error criterion of 6.9%. Average overall CVa for the StatSensor® was 10.4% and 5.2% for capillary and venous whole blood results, respectively. Overall CVa for the central laboratory serum creatinine method was <1.5%. For monitoring renal (dys)function, total agreement of the StatSensor® with an IDMS-traceable enzymatic test was 68% using a 10% Δ change. No significant differences were found between the changes observed by both methods. CONCLUSIONS: Capillary blood testing with the StatSensor® is not advisable for determining current renal function with a single creatinine measurement in kidney transplant patients, mainly due to excessive analytical imprecision. However, our results suggest that capillary blood testing with the StatSensor® can be used for daily trend monitoring of kidney function after renal transplantation.

External Quality Assessment Scheme for reference laboratories - review of 8 years' experience.

We describe an External Quality Assessment Scheme (EQAS) intended for reference (calibration) laboratories in laboratory medicine and supervised by the Scientific Division of the International Federation of Clinical Chemistry and Laboratory Medicine and the responsible Committee on Traceability in Laboratory Medicine. The official EQAS website, RELA (www.dgkl-rfb.de:81), is open to interested parties. Information on all requirements for participation and results of surveys are published annually. As an additional feature, the identity of every participant in relation to the respective results is disclosed. The results of various groups of measurands (metabolites and substrates, enzymes, electrolytes, glycated hemoglobins, proteins, hormones, thyroid hormones, therapeutic drugs) are discussed in detail. The RELA system supports reference measurement laboratories preparing for accreditation according to ISO 17025 and ISO 15195. Participation in a scheme such as RELA is one of the requirements for listing of the services of a calibration laboratory by the Joint Committee on Traceability in Laboratory Medicine.

Results of a European-Wide External Quality Assessment (EQA) Scheme for Serological Detection of Anti-SARS-CoV-2 (CoVimm)-Pitfalls of Routine Application.

BACKGROUND: During the last two years, a variety of assays for the serological detection of antibodies to the new SARS-CoV-2 virus have been launched and used as part of standard care in many laboratories. The pace with which these tests have been introduced into routine care emphasizes the importance of quality measures for analytical methods, particularly with regard to the implications of results for clinical and epidemiologic decisions. Accuracy, reliability and comparability of analytical test results are thus essential, and here external quality assessment (EQA) is the most important quality assurance tool. It allows us to achieve harmonization of test methods as a prerequisite for a high standard of performance for laboratory and analytical techniques and their interpretation. METHODS: This EQA scheme consisted of pre-characterized clinical biospecimens dedicated to the analysis of anti-SARS-CoV-2 IgG total antibodies and differentiation into spike protein-specific IgG antibodies against SARS-CoV-2 (anti-S-SARS-CoV-2) and nucleocapsid-specific IgG antibodies against SARS-CoV-2 (anti-N-SARS-CoV-2). RESULTS: A total of 239 laboratories across Europe participated in this scheme, called CoVimm. In detail, 536 results for anti-SARS-CoV-2 IgG, 431 results for anti-S-SARS-CoV-2 IgG, and 200 results for anti-N-SARS-CoV-2 IgG were reported. Based on the pre-defined thresholds, the success rates for the determination of anti-S-SARS-CoV-2 IgG and anti-N-SARS-CoV-2 IgG were 96% and 90%, respectively. Interestingly, only 64% of the participating laboratories successfully passed the EQA scheme for the determination of total anti-SARS-CoV-2 IgG. CONCLUSIONS: This EQA revealed serious concerns regarding the reliability and appropriate use of anti-SARS-CoV-2 antibody assays in routine care. In addition to the wide heterogeneity of different assays used by participating laboratories, a lack of standardization and harmonization is also evident. This is of particular importance for reliable and clinically meaningful interpretation of test results.

Decision-making in localized prostate cancer: lessons learned from an online support group.

OBJECTIVE: • To investigate patient-to-patient communication with regard to decision-making in localized prostate cancer; as most of it is done in private, online support groups are a unique means for this task. PATIENTS AND METHODS: • Over a 32-month period, we screened 501 threads in the largest German online support group for prostate cancer. • Threads started by questioners newly diagnosed with localized prostate cancer and stating decision-making as the key topic were included; in all, 82 (16.4%) threads met these criteria. • Two independent investigators characterized every thread following a standardized protocol. • Fisher's exact test and Mann-Whitney U-test were applied for group analyses. A complementary qualitative linguistic approach was chosen. RESULTS: • Threads were most commonly started to ask for therapy recommendations (66%), information on the course of treatment (46%) and emotional support (46%). • Answers consisted of treatment recommendations (40%), emotional support (37%) and personal experiences (28%). • A second opinion on the biopsy cores (51%) and additional imaging (40%) were common suggestions. • The rate of advice for radical prostatectomy (RP) vs radiotherapy was 67 vs 82%. Thus, surgery was less recommended in our sample (P = 0.01); 75% of the men with an initial therapeutic preference were finally confirmed herein. • Linguistic analysis showed that posters frequently use a tentative language style and that common language is avoided. CONCLUSIONS: • Patients readily receive information, advice and emotional support as part of an online support group. • The scientific evaluation of an online support group is a complementary way of getting to know our patients' needs and worries. • Patient-physician contact can benefit from this knowledge.

Lung clearance index and diffusion capacity for CO to detect early functional pulmonary impairment in children with rheumatic diseases.

BACKGROUND: In adults with rheumatic diseases pulmonary complications are relevant contributors to morbidity and mortality. In these patients diffusion capacity for CO (DLCO) is an established method to detect early pulmonary impairment. Pilot studies using DLCO indicate that early functional pulmonary impairment is present even in children with rheumatic disease albeit not detectable by spirometry and without clinical signs of pulmonary disease. Since the lung clearance index (LCI) is also a non-invasive, feasible and established method to detect early functional pulmonary impairment especially in children and because it requires less cooperation (tidal breathing), we compared LCI versus DLCO (forced breathing and breath-holding manoeuvre) in children with rheumatic diseases. FINDINGS: Nineteen patients (age 9-17 years) with rheumatic disease and no clinical signs of pulmonary disease successfully completed LCI and DLCO during annual check-up. In 2 patients LCI and DLCO were within physiological limits. By contrast, elevated LCI combined with physiological results for DLCO were seen in 8 patients and in 9 patients both, the LCI and DLCO indicate early functional pulmonary changes. Overall, LCI was more sensitive than DLCO to detect early functional pulmonary impairment (p = 0.0128). CONCLUSIONS: Our findings suggest that early functional pulmonary impairment is already present in children with rheumatic diseases. LCI is a very feasible and non-invasive alternative for detection of early functional pulmonary impairment in children. It is more sensitive and less cooperation dependent than DLCO. Therefore, we suggest to integrate LCI in routine follow-up of rheumatic diseases in children.

Exhaled nitric oxide can't replace the methacholine challenge in suspected pediatric asthma.

BACKGROUND: In adults, measurement of FENO has been recently suggested as a substitute for the methacholine challenge test (MCT) for diagnosis of asthma. This study aimed to evaluate whether FeNO is a substitute for MCH also in children with suspicious asthma. METHODS: During a single visit steroid naive children (5-17 years) with suspicious asthma underwent skin prick test (SPT), FENO measurement and spirometry prior and during MCT (one concentration procedure). Results of the SPT (atopy/non-atopy) and MCT (asthma/non-asthma) were used for categorization. ROC analysis in atopy non-atopy subgroups yielded sensitivity, specificity, positive and negative predictive value (PPV and NPV) for FENO. RESULTS: The SPT revealed atopy in 134 out of 222 children (age 9.7 ±â€¯3.2 years) investigated and asthma was diagnosed in 114 (77/37 atopy/non-atopy) patients. FENO values in patients with atopic asthma were significantly higher compared to those with either non-atopic asthma or atopia without asthma (18 ppb (5-89) vs 7 ppb (5-36); p < 0.001; 18 ppb (5-89) vs 11 ppb (5-98); p < 0.05). Sensitivity and specificity of FENO for diagnosing atopic asthma (FENO≥15.5 ppb; AUC = 0.635, p < 0.01) were 61.1% and 64.9% and non-atopic asthma (FENO≥ 6.5 ppb; AUC = 0.445, p = 0.382) 54.1% and 39.2%, respectively. The PPV/NPV for FENO were 0.70/0.55 in atopy and 0.39/0.54 in non-atopy patients, respectively. CONCLUSION: In children, FENO is not appropriate to substitute for the MCT. However, in patients with a negative SPT a FENO in the normal range makes the presence of atopic asthma unlikely.

Limited comparability of creatinine assays in patients with liver cirrhosis and their impact on the MELD score.

BACKGROUND & AIM: Patients with end-stage liver disease require valid estimations of mortality for organ allocation and risk stratification. The model of end-stage liver disease (MELD) score is used for this purpose in most countries and incorporates bilirubin, International Normalized ratio, and creatinine. The aim of this study was to evaluate the comparability of creatinine results from different routine assays in the serum samples of patients with liver cirrhosis. METHODS: Residual material from 60 serum samples was available from patients in different stages of liver cirrhosis. Four centers participated; each center analyzed the samples with Jaffé-based and enzymatic routine assays in parallel. In addition, an accredited calibration laboratory certified the panel of samples by an internationally accepted reference measurement procedure (RMP) based on isotope dilution mass spectrometry (ID-MS). This method served as the independent reference. RESULTS: All routine methods displayed a high correlation to the RMP (r ≥0.937, p<0.001). Two enzymatic and two Jaffé-based methods provided results that were all within a ±20% range of the RMP. The other methods showed deviations >20% in up to 27% of the samples. The enzymatic methods were systematically lower, whereas the Jaffé-based methods were systematically higher (p<0.001). The resulting MELD scores differed from 0 to 4 points. CONCLUSIONS: There are systematic deviations from the RMP. Jaffé-based assays gave higher results, whereas the enzymatic-based assays gave lower results compared to the results of the RMP. The comparability of results is limited and could be disadvantageous to patients listed for liver transplantation.

Feasibility study of the use of frozen human sera in split-sample comparison of immunoassays with candidate reference measurement procedures for total thyroxine and total triiodothyronine measurements.

BACKGROUND: Diagnostic manufacturers must ensure/document metrologically traceable assays. We report on a feasibility study of a split-sample comparison for that purpose. Processed, frozen single-donation sera, assigned target values by candidate reference measurement procedures (cRMPs), were used with immunoassays for total thyroxine (TT(4)) and triiodothyronine (TT(3)) as models. METHODS: Two serum panels were quantified for TT(4) and TT(3) with validated cRMPs and measured in parallel with at least 14 immunoassays. The results were interpreted in terms of traceability of calibration (trueness) and of the individual measurement result (accuracy) by linear regression analysis and graphical representation against specifications. The commutability of the sera was investigated by parallel analysis of TT(4) in freshly collected but nonfiltered specimens. RESULTS: The TT(4) (TT(3)) concentrations in the sera (according to the cRMPs) were 64-269 nmol/L (0.88-13.7 nmol/L). The method comparison showed that for TT(4), on average, the immunoassays produced results in agreement with the cRMPs, whereas for TT(3), results were typically higher. It also demonstrated a considerable between-assay divergence in traceability of calibration and accuracy. The evidence of noncommutability of the sera attributable to processing, however, indicates that the interpretation should be treated with caution. CONCLUSIONS: Frozen sera can be used for documenting/validating traceability of total thyroid measurements. The way in which the sera are processed may jeopardize commutability, however, and therefore requires in-depth investigation.

Metrologic traceability of total thyroxine measurements in human serum: efforts to establish a network of reference measurement laboratories.

BACKGROUND: Assuring/demonstrating metrologic traceability of in vitro diagnostics necessitates the availability of measurand-specific reference measurement systems (RMSs) and the possibility for industry to work with competent reference measurement laboratories (RMLs). Here we report the results of a European project to investigate the feasibility of developing a RMS for serum total thyroxine. METHODS: Four candidate RMLs (cRMLs) developed/implemented variants of a candidate reference measurement procedure (cRMP) based on isotope dilution-liquid chromatography-mass spectrometry. The sole constraint implemented was calibration with a common thyroxine primary calibrator. The RMPs were externally validated and assessed for comparability in round-robin trials using common samples, i.e., 5 lyophilized and 33 frozen native sera. At the same time, the performance of the cRMLs organized in a network was assessed. For uniform external quality assessment, common performance specifications were agreed on. RESULTS: All cRMLs performed the cRMPs with fulfillment of the predefined specifications: total and between-laboratory CVs < or =2.0% and 2.5%, respectively, and a systematic deviation < or =0.9%, estimated with a target assigned from the mean of means obtained by the cRMLs. The mean expanded uncertainty for value assignment to the native sera was 2.1%. CONCLUSIONS: A network of cRMLs, with externally conformed competence to properly perform RMPs, has been established. Performance specifications were defined and will form the basis for admittance of new network members. A serum panel, successfully targeted during the validation process, is available for split-sample measurements with commercial routine measurement procedures. The model can now be used for other measurands for which traceability to the Systeme International d'Unites is needed.