Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus.

BACKGROUND: Numerous laboratory tests are used in the diagnosis and management of diabetes mellitus. The quality of the scientific evidence supporting the use of these assays varies substantially. APPROACH: An expert committee compiled evidence-based recommendations for laboratory analysis in screening, diagnosis, or monitoring of diabetes. The overall quality of the evidence and the strength of the recommendations were evaluated. The draft consensus recommendations were evaluated by invited reviewers and presented for public comment. Suggestions were incorporated as deemed appropriate by the authors (see Acknowledgments). The guidelines were reviewed by the Evidence Based Laboratory Medicine Committee and the Board of Directors of the American Association of Clinical Chemistry and by the Professional Practice Committee of the American Diabetes Association. CONTENT: Diabetes can be diagnosed by demonstrating increased concentrations of glucose in venous plasma or increased hemoglobin A1c (Hb A1c) in the blood. Glycemic control is monitored by the people with diabetes measuring their own blood glucose with meters and/or with continuous interstitial glucose monitoring (CGM) devices and also by laboratory analysis of Hb A1c. The potential roles of noninvasive glucose monitoring, genetic testing, and measurement of ketones, autoantibodies, urine albumin, insulin, proinsulin, and C-peptide are addressed. SUMMARY: The guidelines provide specific recommendations based on published data or derived from expert consensus. Several analytes are found to have minimal clinical value at the present time, and measurement of them is not recommended.

Executive Summary: Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus.

BACKGROUND: Numerous laboratory tests are used in the diagnosis and management of patients with diabetes mellitus. The quality of the scientific evidence supporting the use of these assays varies substantially. An expert committee compiled evidence-based recommendations for laboratory analysis in patients with diabetes. The overall quality of the evidence and the strength of the recommendations were evaluated. The draft consensus recommendations were evaluated by invited reviewers and presented for public comment. Suggestions were incorporated as deemed appropriate by the authors (see Acknowledgments in the full version of the guideline). The guidelines were reviewed by the Evidence Based Laboratory Medicine Committee and the Board of Directors of the American Association of Clinical Chemistry and by the Professional Practice Committee of the American Diabetes Association. CONTENT: Diabetes can be diagnosed by demonstrating increased concentrations of glucose in venous plasma or increased hemoglobin A1c (Hb A1c) in the blood. Glycemic control is monitored by the patients measuring their own blood glucose with meters and/or with continuous interstitial glucose monitoring devices and also by laboratory analysis of Hb A1c. The potential roles of noninvasive glucose monitoring; genetic testing; and measurement of ketones, autoantibodies, urine albumin, insulin, proinsulin, and C-peptide are addressed. SUMMARY: The guidelines provide specific recommendations based on published data or derived from expert consensus. Several analytes are found to have minimal clinical value at the present time, and measurement of them is not recommended.

Analytical and Non-Analytical Variation May Lead to Inappropriate Antimicrobial Dosing in Neonates: An In Silico Study.

BACKGROUND: Therapeutic drug monitoring (TDM) of aminoglycosides and vancomycin is used to prevent oto- and nephrotoxicity in neonates. Analytical and nonanalytical factors potentially influence dosing recommendations. This study aimed to determine the impact of analytical variation (imprecision and bias) and nonanalytical factors (accuracy of drug administration time, use of non-trough concentrations, biological variation, and dosing errors) on neonatal antimicrobial dosing recommendations. METHODS: Published population pharmacokinetic models and the Australasian Neonatal Medicines Formulary were used to simulate antimicrobial concentration-time profiles in a virtual neonate population. Laboratory quality assurance data were used to quantify analytical variation in antimicrobial measurement methods used in clinical practice. Guideline-informed dosing recommendations based on drug concentrations were applied to compare the impact of analytical variation and nonanalytical factors on antimicrobial dosing. RESULTS: Analytical variation caused differences in subsequent guideline-informed dosing recommendations in 9.3-12.1% (amikacin), 16.2-19.0% (tobramycin), 12.2-45.8% (gentamicin), and 9.6-19.5% (vancomycin) of neonates. For vancomycin, inaccuracies in drug administration time (45.6%), use of non-trough concentrations (44.7%), within-subject biological variation (38.2%), and dosing errors (27.5%) were predicted to result in more dosing discrepancies than analytical variation (12.5%). Using current analytical performance specifications, tolerated dosing discrepancies would be up to 14.8% (aminoglycosides) and 23.7% (vancomycin). CONCLUSIONS: Although analytical variation can influence neonatal antimicrobial dosing recommendations, nonanalytical factors are more influential. These result in substantial variation in subsequent dosing of antimicrobials, risking inadvertent under- or overexposure. Harmonization of measurement methods and improved patient management systems may reduce the impact of analytical and nonanalytical factors on neonatal antimicrobial dosing.

Interference by macroprolactin in assays for prolactin: will the In Vitro Diagnostics Regulation lead to a solution at last?

Cross reactivity with high molecular weight complexes of prolactin known as macroprolactin is a common cause of positive interference in assays for serum prolactin. All prolactin assays currently available are affected with 5-25% of results indicating hyperprolactinaemia falsely elevated due to macroprolactinaemia - hyperprolactinaemia due to macroprolactin with normal concentrations of bioactive monomeric prolactin. Macroprolactinaemia has no pathological significance but, if it is not recognised as the cause, the apparent hyperprolactinaemia can lead to clinical confusion, unnecessary further investigations, inappropriate treatment and waste of healthcare resources. Macroprolactinaemia cannot be distinguished from true hyperprolactinaemia on clinical grounds alone but can be detected by a simple laboratory test based on the precipitation of macroprolactin with polyethylene glycol. Laboratory screening of all cases of hyperprolactinaemia to exclude macroprolactinaemia has been advised as best practice but has not been implemented universally and reports of clinical confusion caused by macroprolactinaemia continue to appear in the literature. Information provided by manufacturers to users of assays for prolactin regarding interference by macroprolactin is absent or inadequate and does not comply with the European Union Regulation covering in vitro diagnostic medical devices (IVDR). As the IVDR is implemented notified bodies should insist that manufacturers of assays for serum prolactin comply with the regulations by informing users that macroprolactin is a source of interference which may have untoward clinical consequences and by providing an estimate of the magnitude of the interference and a means of detecting macroprolactinaemia. Laboratories should institute a policy for excluding macroprolactinaemia in all cases of hyperprolactinaemia.

Harmonization of LC-MS/MS Measurements of Plasma Free Normetanephrine, Metanephrine, and 3-Methoxytyramine.

BACKGROUND: Plasma-free normetanephrine and metanephrine (metanephrines) are the recommended biomarkers for testing of pheochromocytoma and paraganglioma (PPGL). This study evaluated the status of harmonization of liquid chromatography-tandem mass spectrometry-based measurements of plasma metanephrines and methoxytyramine and clinical interpretation of test results. METHODS: 125 plasma samples from patients tested for PPGLs were analyzed in 12 laboratories. Analytical performance was also assessed from results of a proficiency-testing program. Agreement of test results from different laboratories was assessed by Passing-Bablok regression and Bland-Altman analysis. Agreement in clinical test interpretation based on laboratory specific reference intervals was also examined. RESULTS: Comparisons of analytical test results by regression analysis revealed strong correlations for normetanephrine and metanephrine (R ≥ 0.95) with mean slopes of 1.013 (range 0.975-1.078), and 1.019 (range 0.963-1.081), and intercepts of -0.584 (-53.736 to 54.790) and -3.194 (-17.152 to 5.933), respectively. The mean bias between methods was 1.2% (-11.6% to 16.0%) for metanephrine and 0.1% (-18.0% to 9.5%) for normetanephrine. Measurements of 3-methoxytyramine revealed suboptimal agreement between laboratories with biases ranging from -32.2% to 64.0%. Interrater agreement in test interpretation was >94% for metanephrine and >84% for normetanephrine; improvements in interrater agreement were observed with use of harmonized reference intervals, including age-specific cut-offs for normetanephrine. CONCLUSIONS: Analytical methods for metanephrines are well harmonized between laboratories. However, the 16% disagreement in test interpretation for normetanephrine suggests use of suboptimal method-dependent reference intervals for clinical decision-making for this metabolite. Improved analytical methods and reference interval harmonization are particularly required for 3-methoxytyramine.

Reference intervals for venous blood gas measurement in adults.

OBJECTIVES: Venous blood gas (VBG) analysis is becoming a popular alternative to arterial blood gas (ABG) analysis due to reduced risk of complications at phlebotomy and ease of draw. In lack of published data, this study aimed to establish reference intervals (RI) for correct interpretation of VBG results. METHODS: One hundred and 51 adult volunteers (101 females, 50 males, 18-70 years) were enrolled after completion of a health questionnaire. Venous blood was drawn into safePICO syringes and analysed on ABL827 blood gas analyser (Radiometer Pacific Pty. Ltd.). A non-parametric approach was used to directly establish the VBG RI which was compared to a calculated VBG RI based on a meta-analysis of differences between ABG and VBG. RESULTS: After exclusions, 134 results were used to derive VBG RI: pH 7.30-7.43, partial pressure of carbon dioxide (pCO2) 38-58 mmHg, partial pressure of oxygen (pO2) 19-65 mmHg, bicarbonate (HCO3-) 22-30 mmol/L, sodium 135-143 mmol/L, potassium 3.6-4.5 mmol/L, chloride 101-110 mmol/L, ionised calcium 1.14-1.29 mmol/L, lactate 0.4-2.2 mmol/L, base excess (BE) -1.9-4.5 mmol/L, saturated oxygen (sO2) 23-93%, carboxyhaemoglobin 0.4-1.4% and methaemoglobin 0.3-0.9%. The meta-analysis revealed differences between ABG and VBG for pH, HCO3-, pCO2 and pO2 of 0.032, -1.0 mmol/L, -4.2 and 39.9 mmHg, respectively. Using this data along with established ABG RI, calculated VBG RI of pH 7.32-7.42, HCO3- 23 - 27 mmol/L, pCO2 36-49 mmHg (female), pCO2 39-52 mmHg (male) and pO2 43-68 mmHg were formulated and compared to the VBG RI of this study. CONCLUSIONS: An adult reference interval has been established to assist interpretation of VBG results.

IFCC interim guidelines on rapid point-of-care antigen testing for SARS-CoV-2 detection in asymptomatic and symptomatic individuals.

With an almost unremittent progression of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections all around the world, there is a compelling need to introduce rapid, reliable, and high-throughput testing to allow appropriate clinical management and/or timely isolation of infected individuals. Although nucleic acid amplification testing (NAAT) remains the gold standard for detecting and theoretically quantifying SARS-CoV-2 mRNA in various specimen types, antigen assays may be considered a suitable alternative, under specific circumstances. Rapid antigen tests are meant to detect viral antigen proteins in biological specimens (e.g. nasal, nasopharyngeal, saliva), to indicate current SARS-CoV-2 infection. The available assay methodology includes rapid chromatographic immunoassays, used at the point-of-care, which carries some advantages and drawbacks compared to more conventional, instrumentation-based, laboratory immunoassays. Therefore, this document by the International Federation for Clinical Chemistry and Laboratory Medicine (IFCC) Taskforce on COVID-19 aims to summarize available data on the performance of currently available SARS-CoV-2 antigen rapid detection tests (Ag-RDTs), providing interim guidance on clinical indications and target populations, assay selection, and evaluation, test interpretation and limitations, as well as on pre-analytical considerations. This document is hence mainly aimed to assist laboratory and regulated health professionals in selecting, validating, and implementing regulatory approved Ag-RDTs.

The kinetic estimated glomerular filtration rate ratio predicts acute kidney injury.

AIM: Kinetic estimated Glomerular Filtration Rate (KeGFR) approximates GFR under non-steady-state conditions. We investigated whether the ratio of KeGFR difference to baseline eGFR could predict acute kidney injury (AKI) earlier than a creatinine-based algorithm that triggered an AKI electronic Alert (eAlert). METHODS: This retrospective, single-centre, proof-of-concept cohort study assessed all patients diagnosed with AKI by an automated serum creatinine-based eAlert. The kinetic eGFR, the kinetic eGFR difference from baseline and the ratio of difference to baseline was calculated in subjects with at least two serum creatinine (sCr) measurements within 72 h of AKI. RESULTS: Patients in the AKI cohort (n = 140) had a significant decline in KeGFR ratio (AKI: 17% IQR 7% to 29%, Non-AKI: 0 IQR -12% to 9%; P-value <.0001). A decrease of the ratio greater than 10% predicted AKI with a sensitivity of 66%, a specificity of 77%, a positive predictive value of 63%, and negative predictive value of 80%. The median lead time between KeGFR ratio decrease and AKI was 24 h (IQR: 19-27 h). CONCLUSIONS: KeGFR ratio is a cheap, simple method that predicted AKI 24 h before laboratory detection. KeGFR may facilitate triaging patients to increased monitoring or intervention.

Biosafety measures for preventing infection from COVID-19 in clinical laboratories: IFCC Taskforce Recommendations.

Coronavirus disease 2019 (COVID-19) is the third coronavirus outbreak that has emerged in the past 20 years, after severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). One important aspect, highlighted by many global health organizations, is that this novel coronavirus outbreak may be especially hazardous to healthcare personnel, including laboratory professionals. Therefore, the aim of this document, prepared by the COVID-19 taskforce of the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), is to provide a set of recommendations, adapted from official documents of international and national health agencies, on biosafety measures for routine clinical chemistry laboratories that operate at biosafety levels 1 (BSL-1; work with agents posing minimal threat to laboratory workers) and 2 (BSL-2; work with agents associated with human disease which pose moderate hazard). We believe that the interim measures proposed in this document for best practice will help minimazing the risk of developing COVID-19 while working in clinical laboratories.

IFCC Interim Guidelines on Molecular Testing of SARS-CoV-2 Infection.

The diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection globally has relied extensively on molecular testing, contributing vitally to case identification, isolation, contact tracing, and rationalization of infection control measures during the coronavirus disease 2019 (COVID-19) pandemic. Clinical laboratories have thus needed to verify newly developed molecular tests and increase testing capacity at an unprecedented rate. As the COVID-19 pandemic continues to pose a global health threat, laboratories continue to encounter challenges in the selection, verification, and interpretation of these tests. This document by the International Federation for Clinical Chemistry and Laboratory Medicine (IFCC) Task Force on COVID-19 provides interim guidance on: (A) clinical indications and target populations, (B) assay selection, (C) assay verification, and (D) test interpretation and limitations for molecular testing of SARS-CoV-2 infection. These evidence-based recommendations will provide practical guidance to clinical laboratories worldwide and highlight the continued importance of laboratory medicine in our collective pandemic response.

IFCC Interim Guidelines on Serological Testing of Antibodies against SARS-CoV-2.

Serological testing for the detection of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is emerging as an important component of the clinical management of patients with coronavirus disease 2019 (COVID-19) as well as the epidemiological assessment of SARS-CoV-2 exposure worldwide. In addition to molecular testing for the detection of SARS-CoV-2 infection, clinical laboratories have also needed to increase testing capacity to include serological evaluation of patients with suspected or known COVID-19. While regulatory approved serological immunoassays are now widely available from diagnostic manufacturers globally, there is significant debate regarding the clinical utility of these tests, as well as their clinical and analytical performance requirements prior to application. This document by the International Federation for Clinical Chemistry and Laboratory Medicine (IFCC) Taskforce on COVID-19 provides interim guidance on: (A) clinical indications and target populations, (B) assay selection, (C) assay evaluation, and (D) test interpretation and limitations for serological testing of antibodies against SARS-CoV-2 infection. These evidence-based recommendations will provide practical guidance to clinical laboratories in the selection, verification, and implementation of serological assays and are of the utmost importance as we expand our pandemic response from initial case tracing and containment to mitigation strategies to minimize resurgence and further morbidity and mortality.

IFCC Interim Guidelines on Biochemical/Hematological Monitoring of COVID-19 Patients.

Routine biochemical and hematological tests have been reported to be useful in the stratification and prognostication of pediatric and adult patients with diagnosed coronavirus disease (COVID-19), correlating with poor outcomes such as the need for mechanical ventilation or intensive care, progression to multisystem organ failure, and/or death. While these tests are already well established in most clinical laboratories, there is still debate regarding their clinical value in the management of COVID-19, particularly in pediatrics, as well as the value of composite clinical risk scores in COVID-19 prognostication. This document by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) Task Force on COVID-19 provides interim guidance on: (A) clinical indications for testing, (B) recommendations for test selection and interpretation, (C) considerations in test interpretation, and (D) current limitations of biochemical/hematological monitoring of COVID-19 patients. These evidence-based recommendations will provide practical guidance to clinical laboratories worldwide, underscoring the contribution of biochemical and hematological testing to our collective pandemic response.

Under-detection of acute kidney injury in hospitalised patients: a retrospective, multi-site, longitudinal study.

BACKGROUND: Acute kidney injury (AKI) is a rapid deterioration of renal function, often caused by a variety of co-existing morbidities complicating its recognition and treatment, leading to short- and long-term adverse clinical outcomes. There are limited data on the incidence of AKI in Australia using the Kidney Disease Improving Global Outcomes creatinine-based consensus definition. AIM: To determine the incidence and estimate the extent of under-reporting of AKI in four hospitals in the South-Eastern Sydney/Illawarra regions of New South Wales, Australia. METHOD: A laboratory algorithm based on the Kidney Disease Improving Global Outcomes creatinine-based definition for AKI was applied retrospectively to laboratory data for adult patients admitted to the study hospitals between 2009 and 2013 to identify those with AKI. The results were compared with the incidence of AKI based on diagnostic codes for AKI reported for the same period. RESULTS: AKI was detected in 12.4% of all hospitalisations (46 101/370 969) and 16.4% of patients (31 448/192 133) across the 5-year study period using the laboratory algorithm. Of these, 72.1% were AKI Stage 1 (33 246/46101). AKI was coded in only 15.9% of hospitalisations with AKI Stage 1 (5294/33 246), 38.5% of hospitalisations with Stage 2 (2381/6185), and 46.8% with Stage 3 (3120/6670). Yearly incidence of laboratory-identified AKI trended downward between 2009 and 2013, while annual incidence determined by coding trended upward. CONCLUSION: Although coding trends suggested a continuous increase in clinician awareness of AKI across the study period, AKI in hospitalised patients remained significantly under-reported.

An evidence- and risk-based approach to a harmonized laboratory alert list in Australia and New Zealand.

Individual laboratories are required to compose an alert list for identifying critical and significant risk results. The high-risk result working party of the Royal College of Pathologists of Australasia (RCPA) and the Australasian Association of Clinical Biochemists (AACB) has developed a risk-based approach for a harmonized alert list for laboratories throughout Australia and New Zealand. The six-step process for alert threshold identification and assessment involves reviewing the literature, rating the available evidence, performing a risk analysis, assessing method transferability, considering workload implications and seeking endorsement from stakeholders. To demonstrate this approach, a worked example for deciding the upper alert threshold for potassium is described. The findings of the worked example are for infants aged 0-6 months, a recommended upper potassium alert threshold of >7.0 mmol/L in serum and >6.5 mmol/L in plasma, and for individuals older than 6 months, a threshold of >6.2 mmol/L in both serum and plasma. Limitations in defining alert thresholds include the lack of well-designed studies that measure the relationship between high-risk results and patient outcomes or the benefits of treatment to prevent harm, and the existence of a wide range of clinical practice guidelines with conflicting decision points at which treatment is required. The risk-based approach described presents a transparent, evidence- and consensus-based methodology that can be used by any laboratory when designing an alert list for local use. The RCPA-AACB harmonized alert list serves as a starter set for further local adaptation or adoption after consultation with clinical users.

What Alert Thresholds Should Be Used to Identify Critical Risk Results: A Systematic Review of the Evidence.

BACKGROUND: Pathology laboratories are required to immediately report results which indicate a patient is at critical risk, but there is little consensus about what values are deemed critical. The aim of this review was to systematically review the literature on alert thresholds for common chemistry and hematology tests in adults and to provide an explicit and ranked source of this evidence. METHODS: The literature search covered the period of 1995-2014. Evidence sources were critically appraised and ranked using the 1999 Stockholm hierarchy for analytical performance specifications in laboratory medicine modified for establishing decision limits. RESULTS: The 30 most frequently reported laboratory tests with alert thresholds are presented with evidence rankings. Similar thresholds were reported in North America, Europe and Asia. Seventy percent of papers reported thresholds set by individual institutions, while 18% contained thresholds from surveys of laboratories or clinicians. Forty-six percent of the papers referred to 1 or both of the 2 American laboratory surveys from the early 1990s. "Starter sets" of alert thresholds were recommended by 6 professional bodies, 3 of which were collaborations between pathologists and clinicians. None of the 9 outcome studies identified dealt with confounding factors. CONCLUSIONS: Recommendations by professional bodies based on outdated surveys of the former state of the art or consensus are currently the best sources of evidence for laboratories to build their alert list. Well-designed outcome studies and greater collaboration between clinicians and the laboratory are needed to identify the most appropriate alert thresholds that signify actionable, critical or significant risk to patient well-being.

Sex steroid hormone stability in serum tubes with and without separator gels.

BACKGROUND: A pilot study showing a decrease in androstenedione concentration in serum collected into gel-containing serum tubes (STs) triggered an investigation of the effect of serum collection tube on steroid hormone stability. METHODS: In the main study, two tube types were examined: BD Vacutainer® SST™II Advance and BD Vacutainer® Serum Tube. Forty-seven serum samples from apparently healthy volunteers were collected and analysed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) for testosterone, androstenedione, 17-hydroxyprogesterone (17-OHP) (n=20); and oestradiol (n=27). Primary specimens were centrifuged once, maintained at room temperature and extracted within 2 h for day zero (d0) results. To assess stability following refrigeration (2-8 °C), aliquots were taken from the primary tube on day one (d1) and day five (d5) and analysed immediately. Differences in measurand concentration between tubes at d0 and following storage (d1 and d5) were evaluated for statistical significance. RESULTS: There was a progressive and statistically significant decrease in androstenedione concentration from d0 to d5 (p<0.001) in the SST™II tubes. In addition, there was a statistically significant reduction in testosterone, 17-OHP and oestradiol concentrations at d5 (p<0.01). Interestingly, oestradiol and testosterone concentrations increased with time in plain STs (p<0.01). The only change likely to have a clinical impact was that of androstenedione in serum gel tubes. CONCLUSIONS: To optimise conditions and to reduce pre-analytical error we recommend the use of plain serum collection tubes for androstenedione and rapid separation of serum from cells when oestradiol and testosterone are requested.

Multiple reaction monitoring with multistage fragmentation (MRM3) detection enhances selectivity for LC-MS/MS analysis of plasma free metanephrines.

BACKGROUND: LC-MS/MS with multiple reaction monitoring (MRM) is a powerful tool for quantifying target analytes in complex matrices. However, the technique lacks selectivity when plasma free metanephrines are measured. We propose the use of multistage fragmentation (MRM(3)) to improve the analytical selectivity of plasma free metanephrine measurement. METHODS: Metanephrines were extracted from plasma with weak cation exchange solid-phase extraction before separation by hydrophilic interaction liquid chromatography. We quantified normetanephrine and metanephrine by either MRM or MRM(3) transitions m/z 166→134→79 and m/z 180→149→121, respectively. RESULTS: Over a 6-month period, approximately 1% (n = 21) of patient samples showed uncharacterized coeluting substances that interfered with the routine assay, resulting in an inability to report results. Quantification with MRM(3) removed these interferences and enabled measurement of the target compounds. For patient samples unaffected by interferences, Deming regression analysis demonstrated a correlation between MRM(3) and MRM methods of y = 1.00x - 0.00 nmol/L for normetanephrine and y = 0.99x + 0.03 nmol/L for metanephrine. Between the MRM(3) method and the median of all LC-MS/MS laboratories enrolled in a quality assurance program, the correlations were y = 0.97x + 0.03 nmol/L for normetanephrine and y = 1.03x - 0.04 nmol/L for metanephrine. Imprecision for the MRM(3) method was 6.2%-7.0% for normetanephrine and 6.1%-9.9% for metanephrine (n = 10). The lower limits of quantification for the MRM(3) method were 0.20 nmol/L for normetanephrine and 0.16 nmol/L for metanephrine. CONCLUSIONS: The use of MRM(3) technology improves the analytical selectivity of plasma free metanephrine quantification by LC-MS/MS while demonstrating sufficient analytical sensitivity and imprecision.