Total plasma homocysteine measurement: Evaluation of the Abbott immunoassay, comparison with the JEOL ion exchange chromatography and investigation of its clinical utility.

Objectives: Homocysteine is an intermediary amino acid formed in methionine metabolism, with elevated total homocysteine (tHCY) being a biomarker of cardiovascular and cerebrovascular diseases. We evaluated the Abbott ARCHITECT tHCY immunoassay, compared it with the current established JEOL ion exchange chromatography (IEC) method and evaluated its clinical utility. Design and methods: Following immunoassay method verification, plasma samples of 91 patients were analysed for tHCY using immunoassay and IEC. Results: For the Abbott immunoassay, accuracy was assessed, with UK NEQAS EQA specimens, by the correlation of our Abbott immunoassay measurements to the Abbott ARCHITECT immunoassay mean (bias = 1.6%), and to the overall immunoassay mean (bias = 2.0%). The total imprecision was 2.7% (11.00 µmol/L), 2.4% (16.80 µmol/L) and 2.8% (24.30 µmol/L) respectively. Bias in linearity assessment was 0.12%-2.58%. The inter-method correlation was strong in Passing-Bablok regression: immunoassay = IEC x0.857 + 2.445 (95% CI: slope = [0.742,0.947], intercept = [1.340,3.582]), with Spearman correlation = 0.803 (p < 0.001). The Bland-Altman plot showed an average difference of -0.284 µmol/L (95% CI: [-1.043,0.474]) with limits of agreement (mean ± 1.96SD) from -7.425 µmol/L to 6.857 µmol/L.No significant difference in tHCY was found using both methods in patients with cerebrovascular diseases and cardiovascular diseases. Most tHCY measurements were within the reference ranges of both methods. All homocystinuria patients had tHCY values above the reference ranges of both methods. Conclusions: The immunoassay demonstrated robust performance in its verification and showed good comparability with the IEC but with some biases so caution is needed if both are used interchangeably. The immunoassay offers an automated alternative to IEC in the assessment of hyperhomocysteinaemia.

The aldosterone to renin ratio in the diagnosis of primary aldosteronism: Promises and challenges.

The complexity of evaluating patients for secondary treatable causes of hypertension is underappreciated. Primary aldosteronism (PA) is the most prevalent cause of secondary hypertension (3%-32% of hypertensive patients). The recent endocrine society clinical practice guideline (ESCPG), "The Management of Primary Aldosteronism: Case Detection, Diagnosis, and Treatment", differs from the previous version in the explicit recognition of PA as a major public health issue. Despite this, PA is underdiagnosed. The guidelines call on physicians to substantially ramp up the screening of hypertensive patients at risk of PA. Further, it recommends the plasma aldosterone to renin ratio (ARR), as the test of choice for screening for PA. However, the ARR is a highly variable test with reported diagnostic sensitivities and specificities ranging from 66% to 100% and 61% to 100%, respectively. Variability of the ARR can be attributed to the high degree of within-subject variation, differences in sampling protocols, laboratory assays, reporting units, the effect of medications and the population characteristics used to establish the decision thresholds. These factors render the possibility of false positive and false negative results-which have the potential to adversely impact patients. The limitations and caveats to the use of the ARR necessitate an effective clinic-laboratory interface, with specialist physician and clinical scientist collaboration for ARR result interpretation. Improvement in the diagnostic sensitivity and specificity of the ARR is predicated on harmonisation of pretesting patient preparation criteria, knowledge of the analytical methods used to derive the ratio and the method-specific threshold for PA.

Generating method-specific Reference Ranges - A harmonious outcome?

OBJECTIVES: When laboratory Reference Ranges (RR) do not reflect analytical methodology, result interpretation can cause misclassification of patients and inappropriate management. This can be mitigated by determining and implementing method-specific RRs, which was the main objective of this study. DESIGN AND METHODS: Serum was obtained from healthy volunteers (Male + Female, n > 120) attending hospital health-check sessions during June and July 2011. Pseudo-anonymised aliquots were stored (at - 70 °C) prior t° analysis on Abbott ARCHITECT c16000 chemistry and i2000SR immunoassay analysers. Data were stratified by gender where appropriate. Outliers were excluded statistically (Tukey method) to generate non-parametric RRs (2.5th + 97.5th percentiles). RRs were compared to those quoted by Abbott and UK Pathology Harmony (PH) where possible. For 7 selected tests, RRs were verified using a data mining approach. RESULTS: For chemistry tests (n = 23), Upper or Lower Reference Limits (LRL or URL) were > 20% different from Abbott ranges in 25% of tests (11% from PH ranges) but in 38% for immunoassay tests (n = 13). RRs (mmol/L) for sodium (138-144), potassium (3.8-4.9) and chloride (102-110) were considerably narrower than PH ranges (133-146, 3.5-5.0 and 95-108, respectively). The gender difference for ferritin (M: 29-441, F: 8-193 ng/mL) was more pronounced than reported by Abbott (M: 22-275, F: 5-204 ng/mL). Verification studies showed good agreement for chemistry tests (mean [SD] difference = 0.4% [1.2%]) but less so for immunoassay tests (27% [29%]), particularly for TSH (LRL). CONCLUSION: Where resource permits, we advocate using method-specific RRs in preference to other sources, particularly where method bias and lack of standardisation limits RR transferability and harmonisation.

Evaluation of cystatin C in malignancy and comparability of estimates of GFR in oncology patients.

OBJECTIVES: Creatinine is the biomarker of choice for use in estimates of kidney function in oncology patients. However as non-renal factors such as muscle mass can influence creatinine concentrations, we evaluated cystatin C as an alternative biomarker and its incorporation in GFR estimating formulae in an oncology setting. Measured GFR is infrequently undertaken in adult clinical practice with the consequent reliance on calculated GFR for patient assessment. DESIGN AND METHODS: Cystatin C and creatinine concentrations were evaluated from 134 oncology patients prior to commencing chemotherapeutic cycles. Estimates of creatinine clearance (Cockroft-Gault) and GFR (using Hoek, Jonsson, MDRD and CKD-EPI) were evaluated. Cystatin C-based GFR estimates (using CKD-EPI CysC and CKD-EPI SCr/CysC) were compared with the creatinine-based GFR estimates (CG, MDRD and CKD-EPI SCr) within the GFR ranges of 60-89, 45-59 and ≤44 mL/min/1.73 m2. RESULTS: Cystatin C concentrations were significantly higher in oncology patients both prior to commencing chemotherapy (F: P<0.01 and M: P<0.0001) and during cycles of treatment (F: P<0.0001 and M: P<0.01) when compared with a reference population. Cystatin C concentrations also increased significantly during chemotherapy (P<0.0001) in a subset of female patients evaluated. Poor agreement (average 42%) was demonstrated between CKD-EPI CysC and creatinine-based GFR estimates within the investigated GFR ranges, with improved agreement (average 55%) when using the combined CKD-EPI SCr/CysC formula. CONCLUSIONS: This study demonstrated a malignancy and treatment-mediated effect on cystatin C measures, which may confound its clinical utility in estimating GFR in oncology patients.

High-sensitive cardiac troponin-I facilitates timely detection of subclinical anthracycline-mediated cardiac injury.

Background Anthracycline drugs are effective anticancer agents, but their optimal use is limited in many patients by the associated cardiotoxicity, even at designated safe doses. As conventionally sensitive cardiac troponin-I assays fail to reliably quantify concentrations of cardiac troponin-I below 30 ng/L, we investigated the potential role of high-sensitive cardiac troponin-I in the detection of subclinical cardiomyocyte injury in patients treated with anthracycline agents. Methods Serial high-sensitive cardiac troponin-I concentrations were assessed in 84 patients, receiving anthracycline-containing ( n = 38) and non-anthracycline-containing ( n = 46) regimens. Results were assessed for change from pretreatment levels and evaluated according to unisex and gender-specific 99th percentiles (25 ng/L and M: 34 ng/L, F: 16 ng/L, respectively). Results A significant increase in high-sensitive cardiac troponin-I was observed in the anthracycline cohort following five cycles of treatment, with the greatest change correlating to an absolute δ increase of 30.7 ng/L in the early-dose group (early-dose group: P < 0.0001, late-dose group: P < 0.01 and continuous-dose group: P < 0.0001). Doxorubicin dose did not correlate directly with high-sensitive cardiac troponin-I concentrations (Spearman r < -0.22). No significant changes in high-sensitive cardiac troponin-I were reported among the non-anthracycline cohort with all measurements below the 99th percentiles. Conclusions Treatment with anthracycline-based chemotherapeutic regimen demonstrated significant elevations of high-sensitive cardiac troponin-I, indicative of subclinical cardiomyocyte damage. This study demonstrates a role for high-sensitive cardiac troponin-I in evaluating those patients where cardiotoxicity is a concern and a potential future role as a biomarker in optimizing cardioprotective treatments in patients receiving anthracycline therapy.

In control? IQC consensus and statutory regulation.

Purpose - Internal quality control (IQC) represents an essential risk management tool within the total testing pathway (TTP) that contributes to the overall objective of assuring the quality of results produced in medical laboratories. Controlling analytical phase quality alone requires significant expertise and input by scientifically trained staff. This effort has escalated exponentially following the publication of the International Organisation for Standardisation (ISO)15189:2012 requirements for quality and competence in medical laboratories. The reported inconsistency and diversity to IQC approaches in diagnostic laboratories is definitive evidence that international guidance in IQC programme design and implementation is long overdue. The paper aims to discuss these issues. Design/methodology/approach - Herein, the authors define, describe and critically examine the essential elements four stages of an IQC programme and suggest a template to inform both design and ease of implementation. For practical application, the authors have stratified the proposed methodology into four stages: staff education and training; IQC material; IQC targets; and IQC procedure, and provide recommendations that meet ISO15189:2012 requirements. Findings - These recommendations are informed by the published literature together with the collective experience working in clinical biochemistry and diagnostic endocrinology laboratories. The authors note that the laboratory staff's effort on IQC is a continuous process, driven by changes within each IQC stage, in response to risk analysis, maximising economic value or through professional leadership and central to IQC programme implementation and delivery. Practical implications - The authors offer a template that laboratories can use to inform the design and implementation of their IQC programme. Originality/value - The proposed IQC programme is user friendly, flexible and pragmatic with the potential to harmonise practice. The authors have provided a template to potentially harmonise IQC practice nationally. Given the central and critical role that IQC practice plays in ensuring the quality of patient results' importance, the authors contend that the time has come for international consensus and statutory regulation regarding the minimally acceptable criteria for its implementation, monitoring and review.

Laboratory services: regaining and maintaining control.

Purpose - After implementing an internal quality control (IQC) programme, the purpose of this paper is to maintain the requisite analytical performance for clinical laboratory staff, thereby safeguarding patient test results for their intended medical purpose. Design/methodology/approach - The authors address how quality can be maintained and if lost, how it can be regained. The methodology is based on the experience working in clinical laboratory diagnostics and is in accord with both international accreditation requirements and laboratory best practice guidelines. Findings - Monitoring test performance usually involves both prospective and retrospective IQC data analysis. The authors present a number of different approaches together with software tools currently available and emerging, that permit performance monitoring at the level of the individual analyser, across analysers and laboratories (networks). The authors make recommendations on the appropriate response to IQC rule warnings, failures and metrics that indicate analytical control loss, that either precludes further analysis, or signifies deteriorating performance and eventual unsuitability. The authors provide guidance on systematic troubleshooting, to identify undesirable performance and consider risk assessment preventive measures and continuous quality improvement initiatives; e.g., material acceptance procedures, as tools to help regain and maintain analytical control and minimise potential for patient harm. Practical implications - The authors provide a template for use by laboratory scientific personnel that ensures the optimal monitoring of analytical test performance and response when it changes undesirably. Originality/value - The proposed template has been designed to meet the International Organisation for Standardisation for medical laboratories ISO15189:2012 requirements and therefore includes the use of External Quality Assessment and patient results data, as an adjunct to IQC data.

Clinical utility of C-terminal telopeptide of type 1 collagen in multiple myeloma.

Myeloma bone disease (MBD) is a major cause of morbidity in multiple myeloma (MM). We investigated bone turnover markers (BTM) as relapse predictors and biomarkers for monitoring MBD. We measured C-terminal telopeptide of type I collagen (CTX-1), and Procollagen type 1 N Propeptide (P1NP) in 86 MM patients and 26 controls. CTX-1 was higher in newly diagnosed patients compared to control, remission and relapse (P < 0·05), and decreased following treatment. In the setting of relapse, a CTX-1 rise greater than the calculated least significant change (LSC) was observed in 26% of patients 3-6 months prior to relapse (P = 0·007), and in 60·8% up to 3 months before relapse (P = 0·015). Statistically significant changes in CTX-1 levels were also observed in patients who were with and without bisphosphonate therapy at the time of relapse. In patients with normal renal function, mean CTX-1 level was highest in the newly diagnosed group (0·771 ± 0·400 µg/l), and lowest in the remission group (0·099 ± 0·070 µg/l) (P < 0·0001). P1NP levels were not statistically different across the patient groups. We conclude that CTX-1, measured on an automated hospital laboratory platform, has a role in routine treatment monitoring and predicting relapse of MBD, even in patients on bisphosphonates.

Transitioning high sensitivity cardiac troponin I (hs-cTnI) into routine diagnostic use: More than just a sensitivity issue.

OBJECTIVES: High sensitivity cardiac troponin T and I (hs-cTnT and hs-cTnI) assays show analytical, diagnostic and prognostic improvement over contemporary sensitive cTn assays. However, given the importance of troponin in the diagnosis of myocardial infarction, implementing this test requires rigorous analytical and clinical verification across the total testing pathway. This was the aim of this study. DESIGN AND METHODS: Analytical verification included assessment of critical outlier frequency, for hs-cTnI and cTnI assays. Concordance for paired cTnI and hs-cTnI measurements (n=1096) was verified using 99th percentiles for both genders (cTnI: 30 ng/L, hs-cTnI: 25 ng/L) and for men and women separately (hs-cTnI: M: 34;F: 16 ng/L). Discordant data was correlated with clinical and laboratory information. Diagnosis of Acute Coronary Syndrome (ACS) or Non-ACS was adjudicated by two cardiologists independently. RESULTS: The hs-cTnI assay showed a lower (10-fold) critical outlier rate (0.091%) and more detectable results above the limit of detection (LOD) (23.4%) and 99th percentile (2.4%), compared to cTnI. Analytical concordance between the two assays was high (94.5%) but decreased (91.7%) when gender-specific hs-cTnI cut-offs were used. The hs-cTnI assay gave fewer false negatives (up to 1.0%) but disproportionately more false positives (up to 6.7%) overall, which improved (3.9%) for serial measurements. CONCLUSIONS: Laboratories should analytically and clinically verify hs-cTn assays before use, with attention to performance and the clinical and diagnostic algorithms that support appropriate testing and result interpretation. Work in the pre- and post-analytical phases is necessary to augment the analytical improvement in the new era of troponin testing.

Establishment of a reference interval for urinary neutrophil gelatinase-associated lipocalin.

INTRODUCTION: Neutrophil gelatinase-associated lipocalin (NGAL) is emerging as a promising new biomarker for the early identification of acute kidney injury (AKI). We have determined a reference range in a large healthy population. In addition, as NGAL is a neutrophil-related protein, we investigated whether the presence of leukocyturia has the potential to significantly alter the specificity of NGAL in the diagnosis of AKI. METHODS: One hundred and seventy-four subjects (100 men, 74 women ranging from 19 to 88 y) were included in the reference population. Urinary NGAL was analysed on the Abbott ARCHITECT and results expressed in mass (µg/L) and also normalized to urinary creatinine (µg/mmol). Fifty-two leukocyturic urine samples were also analysed for NGAL. RESULTS: The 95th centile for NGAL was determined to be 107 µg/L (13 µg/mmol). There were significant gender-related differences for NGAL, with women having higher concentrations. There were significant age-related differences for NGAL between the 40-59 and 60-88 y age categories. There were significant age-related differences between the <40 and 60-88 y categories when NGAL was normalized to creatinine. In addition, we found significantly higher concentrations of NGAL in leukocyturia (P < 0.0001). CONCLUSIONS: We have established a 95th centile cut-off for urinary NGAL in a reference population. We have demonstrated the important potential interference of leukocyturia in confounding the interpretation of NGAL in the diagnosis of AKI.