Establishing hemolysis, icterus, and lipemia interference limits for body fluid chemistry analytes measured on the Roche cobas instrument

OBJECTIVES

The aims of this study were to (1) establish the maximum allowable interference limits for hemolysis, lipemia, and icterus for chemistry analytes tested in body fluid samples and (2) assess the effectiveness of serial dilution to mitigate spectral interferences.

METHODS

Residual body fluids from clinically ordered testing were mixed (<10% by volume) with stock solutions of interferent (spiked) and compared with a control spiked with an equal volume of 0.9% saline. The analytes were measured on the Roche cobas c501 instrument. Difference and percentage difference were calculated and compared with allowable total error limits. A subset of samples were serially diluted with 0.9% saline. Mean (SD) difference and percentage difference were calculated.

RESULTS

The interference thresholds were lower than the package insert for lactate dehydrogenase, cholesterol, triglycerides, and total protein for hemolysis; amylase, cholesterol, and total protein for icterus; and albumin for lipemia. Only cholesterol and triglyceride results returned to baseline upon dilution of icteric samples.

CONCLUSIONS

Interference thresholds in body fluids were lower than blood for 6 analytes. Diluting interferences that surpass these limits does not produce reliable results that are comparable to the baseline results before spiking in the interferent.

Lack of observed interference by therapeutic monoclonal antibodies in select commonly utilized immunoassays

BACKGROUND

Therapeutic monoclonal antibodies (tmabs) have been hypothesized to interfere with immunoassay measurements, although studies investigating this potential new class of interference are lacking. This study evaluated the effects of tmabs used in cancers ipilimumab (Bristol Myers Squibb), nivolumab (Bristol Myers Squibb), pembrolizumab (Merck) and autoimmune disorders adalimumab (AbbVie), infliximab (Janssen) and vedolizumab (Takeda) in common immunoassays used in the clinical laboratory.

METHODS

Residual sera from 10 randomly chosen patients were split into two tubes and spiked with same volume (approximately 5 % final volume) of either saline (control) or 6 tmabs (final concentration of 100 μg/mL each). Concentrations from sixteen analytes in 19 different assays were assessed: TSH (Roche and Beckman), free thyroxine (Roche and Siemens), cortisol (Beckman), Cancer Antigens (CA): CA19-9 (Beckman), CA15-3 (Roche), CA125 (Roche), and CA27.29 (Siemens), carcinoembryonic antigen (Beckman), alpha-fetoprotein (Beckman), thyroglobulin (Beckman) and thyroglobulin antibodies (Beckman), thyroid peroxidase antibody (Beckman), beta-human chorionic gonadotropin (Roche and Beckman), total prostate-specific antigen (Roche), parathyroid hormone (Roche) and antinuclear antibodies IgG (Werfen). The tmab spiked residual sera were compared with matched saline spiked sera and percent error was assessed against allowable total error defined from biological variation or CLIA limits.

RESULTS

None of the tested immunoassays were affected by the presence of the tmabs, in samples within or outside assay reference intervals. The median % error among all immunoassays ranged between -2.0% (for TSH) to 2.7% (for TPO Ab assay).

CONCLUSION

These findings demonstrate no detectable tmab interference for the assessed immunoassays using spiked preparations of the tmabs in residual human sera. The findings are limited to the tmabs and immunoassays studied here.

A Review of Current Practices and Future Trends in Body Fluid Testing

BACKGROUND

Body fluid testing in the clinical chemistry laboratory is a cornerstone in the diagnostic workup of pathological effusions. Laboratorians may not be aware of the preanalytical workflows used in the collection of body fluids though the value is evident whenever processes change or issues arise. The analytical validation requirements can vary depending on the regulations dictated by the laboratories' jurisdiction and accreditor requirements. Much of analytical validation hinges on how useful testing is to clinical care. Usefulness of testing varies with how well established and incorporated the tests and interpretation are in practice guidelines.

CONTENT

Body fluid collections are depicted and described so clinical laboratorians have a basic appreciation of what specimens are submitted to the laboratory for testing. A review of validation requirements by major laboratory accreditation entities is presented. A review of the usefulness and proposed decision limits for common body fluid chemistry analytes is presented. Body fluid tests that show promise and those that are losing (or lost long ago) value are also reviewed.

SUMMARY

The total testing process from collection to result interpretation can be complicated and easily overlooked by the clinical laboratory. This review aims to improve the understanding and awareness of collections, validation, result interpretation, and provide an update on recent trends.

Population-Based Evaluation of Total Protein in Cerebrospinal Fluid

OBJECTIVES

To present a normal range of cerebrospinal fluid (CSF) protein levels in a community-based population and to evaluate factors that contribute to CSF protein level variability.

PATIENTS AND METHODS

Samples of CSF protein were obtained from participants aged 32 to 95 years who underwent lumbar puncture (LP) between November 1, 2007, and October 1, 2017, as part of the Mayo Clinic Study of Aging, a longitudinal, population-based study of residents of Olmsted County, Minnesota.

RESULTS

A total of 633 participants (58.1% male; 99.1% White; mean ± SD age, 70.9±11.6 years) underwent LP with recorded CSF protein level. Mean ± SD CSF protein level was 52.2±18.4 mg/dL (to convert to mg/L, multiply by 10), with a 95% reference interval of 24.0 to 93.4 mg/dL (range, 14.0-148.0 mg/dL). Spinal stenosis and arterial hypertension were associated with higher CSF protein levels on univariable analysis (P<.001). Increasing age, male sex, and diabetes were all independently associated with higher CSF protein levels on multivariable analysis (P<.001). In the 66 participants with repeated LPs within 2.5 years, the coefficient of repeatability was 26.1 mg/dL. Eleven participants (16.7%) had a CSF protein level difference of 20 mg/dL or more between serial LPs, and 4 (6.1%) had a difference of 25 mg/dL or more. There was a trend toward greater CSF protein level variability in patients with spinal stenosis (P=.054).

CONCLUSION

This large population-based study showed that CSF protein level can vary significantly among individuals. Elevated CSF protein level was independently associated with older age, male sex, and diabetes and is higher than listed in many laboratories. These findings emphasize the necessity of evidence-based reevaluation and standardization of CSF protein metrics.

Comparison of Five Common Analyzers in the Measurement of Chemistry Analytes in an Authentic Cohort of Body Fluid Specimens

OBJECTIVES

Interpretation of body fluid (BF) results is based on published studies and clinical guidelines. The aim of this study is to determine whether the assays from five common commercial vendors produce similar results in BFs for 12 analytes in a BF cohort.

METHODS

BFs (n = 25) and serum (n = 5) were analyzed on five instruments (Roche cobas c501, Ortho 5600, Beckman AU5800 and DXI800, Siemens Vista 1500, and Abbott Architect c8000) to measure albumin, amylase, total bilirubin, cholesterol, creatinine, glucose, lactate dehydrogenase (LDH), lipase, total protein, triglycerides, urea nitrogen, and carcinoembryonic antigen. Deming regression and Bland-Altman analysis were used for method comparison to Roche.

RESULTS

Results were significantly different from Roche for LDH and lipase on Ortho and lipase on Siemens but similar for both BFs and serum. BF differences were larger than serum differences when measuring creatinine, glucose, and urea nitrogen on Ortho and glucose on Siemens.

CONCLUSIONS

Five instruments used to perform BF testing produce results that are not significantly different except for lipase and LDH measurements. Bias of similar magnitude observed in both BF and serum should not affect interpretation. Further investigations into Ortho and Siemens measuring glucose and Ortho measuring creatinine and urea nitrogen are warranted.

Investigation of the correlation between immature reticulocyte fraction and reticulocyte hemoglobin content with common tests for iron deficiency anemia

Reticulocyte hemoglobin content (Ret-He, the hemoglobin within reticulocytes or immature red blood cells) and immature reticulocyte fraction (IRF, the immature fraction of the absolute-reticulocyte-count) are tests that provide insight into erythropoiesis and iron status earlier than conventional iron studies offering the added benefit of not being acute-phase-reactants. Studies have shown that Ret-He is a diagnostic marker for iron-deficiency-anemia (IDA), but fewer studies have investigated IRF. Our laboratory is currently planning to report these parameters when reticulocyte is ordered. Since these are new parameters, we wanted to investigate their overall correlation with complete blood count (CBC) and other iron studies to gain a better appreciation of their utility in our patient population. The aim of this study was to compare the overall correlation of Ret-He and IRF with seven tests used in the evaluation of IDA. To our knowledge these parameters have not all been directly correlated within a single study. CBC and reticulocytes were quantified using XN 9000 hematology analyzers (Sysmex Corporation), ferritin (DXI 800, Beckman Coulter Inc.), and % iron-saturation (measured using total iron-binding-capacity (TIBC)=transferrin*1.18 on Cobas 6000, Roche Diagnostics). Two de-identified cohorts of patients undergoing physician-ordered reticulocyte testing were used for this analysis. Dataset 1 (DS1): (N=2026 from Mayo Clinic Florida) had Ret-He and IRF compared to absolute-reticulocyte-count (Ret), ferritin and % iron saturation. Dataset 2 (DS2): (N=3990 from Mayo Clinic Rochester) had Ret-He and IRF compared to the red-cell-indices of the CBC including hemoglobin (Hgb), mean-corpuscular-volume (MCV), mean-corpuscular-hemoglobin (MCH), and mean-corpuscular-hemoglobin-concentration (MCHC). Correlation coefficients were calculated using Spearman rank-order (ρ) wherein values below +/-0.39 are weak, between +/-0.40-0.59 are considered moderate, and values above +/-0.60 are considered strong. For DS1, Ret-He demonstrated the following correlations: Ret (ρ=0.01), ferritin (ρ=0.33), % iron saturation (ρ=0.63). IRF demonstrated: Ret (ρ=0.46), ferritin (ρ=-0.05), % iron saturation (ρ=-0.22). For DS2, Ret-He demonstrated the following correlations: Hgb (ρ=0.17), MCV (ρ=0.64), MCH (ρ=0.74), MCHC (ρ=0.56). IRF demonstrated Hgb (ρ=-0.41), MCV (ρ=0.10), MCH (ρ=0.04), MCHC (ρ=-0.11). Ret-He and IRF demonstrated different correlative profiles suggesting they may have differing uses. Ret-He was strongly positively-correlated with % iron saturation, MCV, MCH and moderately positively-correlated with MCHC. These positive-correlations are consistent with relationships established in the literature. Interestingly, Ret-He was only weakly correlated with ferritin, possibly owing to ferritin being an acute-phase-reactant. IRF had a moderate positive correlation with Ret and moderate inverse correlation with Hgb. Both of these IRF relationships are consistent with other reports, but both relationships have not been shown in the same study before, preventing direct comparison until now. The literature suggests IRF may have more potential in monitoring treatment than in diagnosis. One limitation of these datasets is their lack of clinical correlation such as established iron-deficiency, anemia status, or treatment information.

Biological Variability of Small Dense LDL, HDL3, and Triglyceride-Rich Lipoprotein Cholesterol

The guideline-recommended lipid panel for cardiovascular disease (CVD) risk assessment measures total cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, and calculated low-density lipoprotein (LDL) cholesterol. Measured cholesterol in subfractions of HDL and LDL purportedly improve CVD risk prediction. Homogenous enzymatic methods are now available for measurement of the cholesterol within small dense LDL (sLDL), small dense HDL (HDL3), and triglyceride-rich lipoproteins (TRL). For meaningful interpretation of these measurements, an understanding of the potential sources and extent of result variability is needed. The smallest difference between serial measurements within a patient that likely reflects a change in clinical status is called the reference change value (RCV). Biological variability and reference change values (RCV) are well-characterized for basic lipids but there is limited information for sLDL, HDL3 or TRL. The objective of this study was to determine intra- and inter-individual variability for sLDL, HDL3, and TRL in a healthy reference population. Serum samples were collected from 24 healthy subjects (n=14 female/10 male) daily for three days (non-fasting), daily for five days (fasting), weekly for four weeks (fasting), and monthly for 7 months (fasting). sLDL, HDL3, and TRL cholesterol were measured in duplicate by enzymatic colorimetric assays (Denka, Japan) on a Roche Cobas c501. Each source of variability (between subject, within subject, and analytical) was calculated using random-effects regression models to estimate each variance component including the overall variation, standard deviation (SD), coefficient of variation (CV), and proportion of total variance (between-subject, within-subject, and analytical). Using these analytical and biological variances, the reference change value (RCV), index of individuality (IoI), and intraclass correlation coefficient (ICC) were determined. Analytic variability (CVa) from monthly testing was 1.2%, 1.1%, and 1.5% for sLDL, HDL3, and TRL, respectively. Monthly within-subject variability (CVw) was 17.1% for sLDL, 7.4% for HDL3 and 25.7% for TRL. Monthly between-subject variability (CVb) was 32.2%, 13.93%, and 33.4% for sLDL, HDL3, and TRL, respectively. Most of the monthly variation was attributed to between-subject variation for all three tests. Within-subject variation accounted for 37% of TRL variation and 22% for both sLDL and HLD3. Within-subject RCVs for monthly measurements were 16.9mg/dL for sLDL, 5.3mg/dL for HDL3, and 15.1mg/dL for TRL. IoIs for monthly testing were 0.81 for TRL, 0.57 for sLDL, and 0.61 for HDL3. Our data demonstrate that sLDL, HDL3, and TRL show low analytical variability, moderate within-subject variability, but high between-subject variability when measured by homogenous assays in a healthy population. The IoI value (&gt;0.6) for TRL suggests use of a reference interval is appropriate for result interpretation. Conversely, clinical cut-points may be more useful than reference intervals for sLDL and HDL3 which had IoIs ~0.6. These findings may be useful for clinical interpretation, particularly when comparing successive measurements of these analytes.

Effect of pH on the Quantification of Common Chemistry Analytes in Body Fluid Specimens Using the Roche cobas Analyzer for Clinical Diagnostic Testing

OBJECTIVES

To determine the influence of pH on recovery of analytes in body fluids (BFs), investigate the mechanism of pH interference, measure the frequency of abnormal-pH BFs received, and compare pH measured by meter and paper.

METHODS

We performed pH titration in residual BFs. A low-pH BF was spiked and neutralized to investigate pH interference. We measured analytes on a Roche cobas c501 analyzer (Roche Diagnostics) and calculated the percent recovery. Measurement of pH using a meter and paper was conducted on 122 BF samples received in the laboratory.

RESULTS

Enzyme activity in BFs was unaffected when pH = 7.4-8.5 lactate dehydrogenase, pH = 7.3-10.2 amylase, pH = 6.0-9.9 lipase, and pH = 1.3-11.7 all other analytes. BFs had mean (range) pH of 8.0 (5.1-8.9), with a mean (range) difference (paper ‒ meter) of ‒0.4 (‒0.6 to 1.1).

CONCLUSIONS

Irreversible loss of enzyme activity occurs in BFs at low pH. Few clinical BFs have pH < 7.0, but laboratories should incorporate pH measurement in BF workflows.

COVID-19 Mortality Prediction From Deep Learning in a Large Multistate Electronic Health Record and Laboratory Information System Data Set: Algorithm Development and Validation

Background

COVID-19 is caused by the SARS-CoV-2 virus and has strikingly heterogeneous clinical manifestations, with most individuals contracting mild disease but a substantial minority experiencing fulminant cardiopulmonary symptoms or death. The clinical covariates and the laboratory tests performed on a patient provide robust statistics to guide clinical treatment. Deep learning approaches on a data set of this nature enable patient stratification and provide methods to guide clinical treatment.

Objective

Here, we report on the development and prospective validation of a state-of-the-art machine learning model to provide mortality prediction shortly after confirmation of SARS-CoV-2 infection in the Mayo Clinic patient population.

Methods

We retrospectively constructed one of the largest reported and most geographically diverse laboratory information system and electronic health record of COVID-19 data sets in the published literature, which included 11,807 patients residing in 41 states of the United States of America and treated at medical sites across 5 states in 3 time zones. Traditional machine learning models were evaluated independently as well as in a stacked learner approach by using AutoGluon, and various recurrent neural network architectures were considered. The traditional machine learning models were implemented using the AutoGluon-Tabular framework, whereas the recurrent neural networks utilized the TensorFlow Keras framework. We trained these models to operate solely using routine laboratory measurements and clinical covariates available within 72 hours of a patient’s first positive COVID-19 nucleic acid test result.

Results

The GRU-D recurrent neural network achieved peak cross-validation performance with 0.938 (SE 0.004) as the area under the receiver operating characteristic (AUROC) curve. This model retained strong performance by reducing the follow-up time to 12 hours (0.916 [SE 0.005] AUROC), and the leave-one-out feature importance analysis indicated that the most independently valuable features were age, Charlson comorbidity index, minimum oxygen saturation, fibrinogen level, and serum iron level. In the prospective testing cohort, this model provided an AUROC of 0.901 and a statistically significant difference in survival (P<.001, hazard ratio for those predicted to survive, 95% CI 0.043-0.106).

Conclusions

Our deep learning approach using GRU-D provides an alert system to flag mortality for COVID-19–positive patients by using clinical covariates and laboratory values within a 72-hour window after the first positive nucleic acid test result.

Proposed Plasma Ammonia Reference Intervals in a Reference Group of Hospitalized Term and Preterm Neonates

BACKGROUND

Plasma ammonia is commonly measured in the diagnostic evaluation of hospitalized newborns, but reference values are not well defined.

METHODS

We prospectively enrolled newborns admitted to the level III/IV neonatal intensive care unit and level II intermediate special care nursery from January 2017 to January 2018. Infants with inborn errors of metabolism or liver disease were excluded. Plasma ammonia concentrations were measured once within the first week of life and evaluated by sex, gestational age, timing of the draw, blood collection method, and type of nutrition. Reference intervals were calculated.

RESULTS

127 neonates were included; one third (34%) were term infants born at ≥37 weeks gestation, and two thirds (66%) were born preterm at <37 weeks gestation. Median plasma ammonia concentrations were 32 μmol/L (range <10 to 86 μmol/L). Median ammonia concentrations were higher among preterm compared to term infants (35 vs. 28 μmol/L, p = 0.0119), and term female compared to term male infants (34 vs. 26 μmol/L, p = 0.0228). There was no difference in median ammonia concentrations between female and male preterm infants, based on gestational age within the preterm group, timing of the blood draw, presence of hyperbilirubinemia, blood collection method, or type of nutritional intake.

CONCLUSIONS

Plasma ammonia concentrations among newborns are higher than the expected adult concentrations and may vary by gestational age and sex. Blood collection method, type of nutrition, hyperbilirubinemia, and timing of the draw do not impact concentrations. We propose a reference limit of ≤82 μmol/L for newborns less than one week of age.

Synovial fluid α defensin has comparable accuracy to synovial fluid white blood cell count and polymorphonuclear percentage for periprosthetic joint infection diagnosis

AIMS

The aim of this study was to determine the diagnostic accuracy of α defensin (AD) lateral flow assay (LFA) and enzyme-linked immunosorbent assay (ELISA) tests for periprosthetic joint infection (PJI) in comparison to conventional synovial white blood cell (WBC) count and polymorphonuclear neutrophil percentage (PMN%) analysis.

METHODS

Patients undergoing joint aspiration for evaluation of pain after total knee arthroplasty (TKA) or total hip arthroplasty (THA) were considered for inclusion. Synovial fluids from 99 patients (25 THA and 74 TKA) were analyzed by WBC count and PMN% analysis, AD LFA, and AD ELISA. WBC and PMN% cutoffs of ≥ 1,700 cells/mm³ and ≥ 65% for TKA and ≥ 3,000 cells/mm³ and ≥ 80% for THA were used, respectively. A panel of three physicians, all with expertise in orthopaedic infections and who were blinded to the results of AD tests, independently reviewed patient data to diagnose subjects as with or without PJI. Consensus PJI classification was used as the reference standard to evaluate test performances. Results were compared using McNemar's test and area under the receiver operating characteristic curve (AUC) analysis.

RESULTS

Expert consensus classified 18 arthroplasies as having failed due to PJI and 81 due to aseptic failure. Using these classifications, the calculated sensitivity and specificity of AD LFA was 83.3% (95% confidence interval (CI) 58.6 to 96.4) and 93.8% (95% CI 86.2 to 98.0), respectively. Sensitivity and specificity of AD ELISA was 83.3% (95% CI 58.6 to 96.4) and 96.3% (95% CI 89.6 to 99.2), respectively. There was no statistically significant difference between sensitivity (p = 1.000) or specificity (p = 0.157) of the two AD assays. AUC for AD LFA was 0.891. In comparison, AUC for synovial WBC count, PMN%, and the combination of the two values was 0.821 (sensitivity p = 1.000, specificity p < 0.001), 0.886 (sensitivity p = 0.317, specificity p = 0.011), and 0.926 (sensitivity p = 0.317, specificity p = 0.317), respectively.

CONCLUSION

The diagnostic accuracy of synovial AD for PJI diagnosis is comparable and not statistically superior to that of synovial WBC count plus PMN% combined. Cite this article: Bone Joint J 2021;103-B(6):1119-1126.

Comparative analysis of 23 synovial fluid biomarkers for hip and knee periprosthetic joint infection detection

There is interest in novel synovial fluid biomarkers for the detection of periprosthetic joint infection (PJI). Here, we assessed the diagnostic accuracy of 23 simple or sophisticated synovial fluid biomarkers for periprosthetic hip or knee infection detection. One hundred seven subjects were studied, 57 of whom had aseptic failure (AF) and 50 PJI. The following synovial fluid biomarkers were tested using spectrophotometric assays, immunoassays, lateral flow tests, or test strips: leukocyte count, monocyte percentage, lymphocyte percentage, neutrophil percentage, C-reactive protein (CRP), glucose, lactate, granulocyte-macrophage colony-stimulating factor, interferon-γ, interleukin-1β (IL-1β), IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12p70, IL-13, IL-17A, IL-23, tumor necrosis factor-α, α-defensin, and leukocyte esterase. The best-performing synovial fluid biomarkers to differentiate PJI from AF-that is, those with highest area under the curve compared to all other biomarkers-were leukocyte count, percent neutrophils and percent monocytes, CRP, and α-defensin (P < .0001).

Human chorionic gonadotropin suspected heterophile interference investigations in immunoassays: a recommended approach

Background Heterophile antibody (HAb) interferences in immunoassays can cause falsely elevated hCG concentrations leading to incorrect diagnosis and treatments options. When results are not consistent with the clinical findings, hCG HAb interference investigation may be requested by the physician. A retrospective evaluation of the frequency of HAb interference was performed among cases of physician-requested investigations and the effectiveness of commercially available blocking reagents to detect HAb interference in two immunoassay systems was evaluated. Methods One hundred and thirteen physician requests for hCG HAb investigation from 2008 to 2017 were reviewed. The primary method used to measure hCG was the Beckman Coulter Access Total βhCG (2008-2010) and the Roche Elecsys HCG+β (2014-2017). HAb investigation included measurement by two immunoassays before and after treatment of samples with heterophile blocking reagents and serial dilution studies. Results Five cases of HAb and HAb-like interference were identified. The interference frequency was 6.7% for the Beckman assay and 2.9% for the Roche assay. The presence of HAb was detected using heterophile blocking reagents and an alternative method in three cases. The other two cases were detected due to discrepant results with an alternative method and non-linear serial dilutions (HAb-like). Conclusions HAb interference was observed in the Beckman and the Roche assays. The heterophile blocking reagents failed to detect 40% of interference cases. Blocking reagents should not solely be used for these investigations. Multiple strategies including the use of serial dilutions and using an alternative platform are critical when troubleshooting interferences in hCG immunoassays.

Analytical Evaluation of BioRad D-100 HPLC Analyzer and Workflow Comparison to BioRad TurboLink Variant II HPLC With Reflex to Boronate Affinity

Introduction

Measurement of hemoglobin A1c (HbA1C) is used for the diagnosis and management of patients with diabetes. Methods for measuring HbA1C are classified on the basis of charge differences (cation exchange chromatography) or structural differences (boronate affinity chromatography). Some cation exchange high-performance liquid chromatography (HPLC) analyzers may be prone to interferences from hemoglobin variants. Historically, our lab used two methods to report HbA1C results: cation exchange HPLC (VariantII) with reflex to boronate affinity HPLC (Ultra2) methods. A new analyzer (BioRad D-100) with improved interference detection and thresholds for interference was evaluated. The objectives of this study were (1) assess the comparability of HbA1c results between D-100, VariantII, and Ultra2; (2) evaluate the need for maintaining a reflex method; and (3) calculate cancellation rates before and after implementing D-100.

Methods

HbA1c was measured by cation exchange methods using VariantII Turbolink, D-100 (BioRad), and boronate affinity using Ultra2Affinity (Trinity Biotech) according to the manufacturer’s recommendations with the following analytical measuring ranges (AMRs), 4.0% to 17.6%, 4.0% to 18.0%, and 4.0% to 17.6%, respectively. D-100 was compared to VariantII (n = 26) and Ultra2 (n = 31) using residual patient samples from provider-ordered HbA1c having no chromatography flags and with the following chromatography flags on VariantII (n = 113): variant window (n = 41), HbA1c <4.0% (n = 24), HbA1a + HbA1b >5% (n = 19), HbF >5% (n = 9), P3 >10% (n = 6), HbA1c >17.6% (n = 4), unknown peak (n = 3), labile 5% to 15% (n = 3), labile >15% (n = 3), and HbS >60% (n = 1). The cancelation rates were calculated at baseline (January 1-31, 2018) and postimplementation of D-100 (September 20, 2018, to January 22, 2019).

Results

HbA1c results from D-100 were within ±0.3 or 5% with the following frequencies: Ultra2 in 96.2% (25/26) with VariantII in 96.8% (30/31) using samples with no chromatography flags. A total of 113 samples with abnormal VariantII flags were tested using D-100 with 82% (n = 92) not exceeding interference limits for result reporting. These D-100 results were within ±0.3 or 5% of Ultra2 results with the following frequencies: 38.5% (10/26) of samples below (n = 23) or above (n = 3) the AMR, 85.3% (29/34) of results with Hb variant flags, 68.0% (17/25) with unknown/minor peaks, and 71.4% (5/7) with HbF <15%. The clinical concordance was also assessed according to the following decision limits: normal <5.6%, prediabetic = 5.7% to 6.4%, and diabetic >6.5%. Results were concordant in 88% with variant peaks (12/13 w/HbA1c <5.6%, 8/11 w/HbA1c = 5.7%-6.4%, 10/10 w/HbA1c >6.5%), 84% with minor peaks (5/6 w/HbA1c <5.6%, 0/2 w/HbA1c = 5.7%-6.4%, 16/17 w/HbA1c >6.5%), and 86% with HbF (3/3 w/HbA1c <5.6%, 2/3 w/HbA1c = 5.7%-6.4%, 1/1 w/HbA1c >6.5%). Results above/below AMR had 100% concordance (>16.0% or <4.4%). The frequency of VariantII rule violation was 2.1% in January 2018, with 53 of 117 having results confirmed as <4.0% or >16.0% by Ultra2, 2 of 117 reported by Ultra2, and 62 being cancelled due to HbF >15% (n = 23) or variant Hb >60% (n = 39). The frequency of rule violation using only D-100 since implementation was 2.2%.

Conclusion

Implementation of D-100 has removed the need for boronate affinity reflex testing and maintained similar cancellation rates.

Effect of pH on the Quantification of Body Fluid Analytes for Clinical Diagnostic Testing

Background

Body fluid samples (BFs) with low pH have demonstrated underrecovery of enzyme activity. The aims of this study were (1) measure the frequency of abnormal pH in BFs received for clinical chemistry testing, (2) calculate recovery of analytes in BFs undergoing pH titration, and (3) investigate the mechanism of pH interference.

Methods

Residual BFs submitted for physician-ordered testing to the Central Clinical Laboratory (Mayo Clinic) were utilized for this study. BFs were centrifuged 10 minutes (3,200 rpm) prior to pH measurement (pH meter, Accumet X15; Fisher Scientific) and analysis. A Roche Cobas c501 (Roche Diagnostics) analyzer was used to measure amylase, lactate dehydrogenase (LDH), blood urea nitrogen (BUN), creatinine, glucose, albumin, total protein, bilirubin (all Roche Diagnostics reagents), and lipase (Sekisui Diagnostics). pH was measured in 122 BFs received between 10/23/2018 and 10/26/2018 within 24 hours of receipt. pH titration was performed using pooled BFs of similar source/type. Each pool was titrated over a range of pH (≤2 to ≥10) in 1-unit increments by addition of a fixed volume of acid (6M HCL) or base (6M NaOH). Analytes were measured before and after acid/base addition. Average percent recovery was calculated (measured/expected × 100%) from n = 3 to 9 pH measurements. A low pH BF pool was spiked (<5% by volume) with a high-concentration BF to investigate mechanism of enzyme underrecovery. Additionally, low pH BF pool was neutralized by addition of base and % recovery calculated. For all titration/spiking experiments, a control sample having the same volume of diluent (7% bovine serum albumin or saline) was used to account for the effects of dilution.

Results

BFs received (n = 122) had mean (SD) pH = 8.0 (0.6) with 6.6% (n = 8) having pH <7.0 and 2.5% (n = 3) having pH <6.0. All recovery (%) and pH data are expressed as mean (range) values. Amylase recovery (initial pH = 8.4-8.9) was 1.3 (0.9-2.2)% at pH = 1.6 (1.0-2.2) (n = 6), 55.6 (37.4-67.0)% at pH = 4.4 (3.5-5.4) (n = 6), 81.4 (74.0-85.2)% at pH = 6.2 (6.1-6.5) (n = 3), 90.1 (84.4-95.4)% at pH = 7.5 (7.3-7.7) (n = 3), 98.8 (96.2-101.7)% at pH = 10.0 (9.8-10.2) (n = 3), and 14.5 (1.4-38.9)% at pH = 11.9 (11.5-12.1) (n = 3). LDH recovery (initial pH = 8.2-8.5) was 1.4 (0.1-3.7)% at pH = 1.7 (1.0-2.4) (n = 6), 18.3 (0.5-39.7)% at pH = 4.5 (3.5-5.4) (n = 6), 63.6 (54.9-68.4)% at pH = 6.2 (6.1-6.5) (n = 3), 85.9 (80.2-90.7)% at pH = 7.2 (6.8-7.4) (n = 3), 46.1 (36.4-61.0)% at pH = 10.0 (9.8-10.2) (n = 3), and 9.8 (0.0-28.9)% at pH = 11.3 (10.4-12.1) (n = 3). Lipase recovery (initial pH = 8.2-8.9) was 10.4 (<1-18)% at pH = 1.8 (1.0-2.4) (n = 6), 73.9 (62.6-85.5)% at pH = 4.2 (3.4-5.2) (n = 3), 92.4 (90.8-93.5)% at pH = 6.2 (6.0-6.5) (n = 3), 96.3 (95.6-96.8)% at pH = 7.3 (6.8-7.7) (n = 3), and 92.9 (89.3-96.8)% at pH = 9.9 (9.8-10.1) (n = 3) and 80.9 (0.0-78.6)% at pH = 11.3 (10.4-12.1) (n = 3). Creatinine, BUN, albumin, glucose, total protein, and bilirubin recovery were 97.9 (92.2-102.9)%, 100 (96.6-103.1)%, 99.9 (97.6-102.4)%, 100.2 (97.8-103)%, 100.2 (98.7-101.9)%, and 100.1 (92.-105.9)%, respectively, between pH 1.3-11.7 (n = 9). Recovery of amylase, LDH, or lipase was <1% after spiking enzymes into BF pool with pH <3. pH adjustment to normal (pH = 8.6-9.0) also resulted in recovery of <1%.

Conclusion

Enzyme activity in BFs was not affected (90%-110% recovery) when pH = 7.4-8.5 for LDH, pH = 7.3-10.2 for amylase, pH = 6.0-9.9 for lipase, and pH = 1.3-11.7 for all other analytes. An irreversible loss of enzyme activity occurs at low pH. Few clinical BFs have pH <7.0, but laboratories should have awareness.

Impact of an electronic decision support rule on ESR/CRP co-ordering rates in a community health system and projected impact in the tertiary care setting and a commercially insured population

INTRODUCTION

Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are common laboratory assays used as markers of inflammation. ESR suffers from higher false positive and false negative rates than CRP. To that end, the American Board of Internal Medicine's (ABIM's) Choosing Wisely campaign has recommended against ESR testing for those with undiagnosed conditions in favor of CRP testing. This study describes the impact of a computerized provider order entry (CPOE) decision support rule against ESR/CRP co-ordering within a community health system that predates the ABIM's Choosing Wisely national guidance. To demonstrate the potential impact of such a CPOE rule within other healthcare settings, ESR/CRP ordering data from a multi-site tertiary care practice and from the commercially insured population in the OptumLabs® Data Warehouse (OLDW) were analyzed and the relative reduction in ESR/CRP co-ordering achieved within the community health system was projected onto these populations.

MATERIALS AND METHODS

ESR and/or CRP orders from a community health system were assessed from 2012 to 2016. Co-ordering and test concordance rates between ESR and CRP were compared before and after CPOE decision support rule launch. Similarly, ESR/CRP co-ordering across three tertiary care sites from 2015 to 2016 and the OLDW from 2009 to 2013 were assessed and the co-ordering rate reduction achieved in the community health system was mathematically projected onto these populations. Estimated payer savings from the rule's effect were calculated within each population using Medicare reimbursement rates.

RESULTS

The CPOE decision support rule realized an unadjusted 42% relative rate reduction in ESR/CRP co-ordering within the community health system yielding an annual payer savings of $15,000 with a modest increase in ESR/CRP concordance rates. Projecting a 40% relative reduction in ESR/CRP co-ordering rates from a similarly effective CPOE rule, annual payer cost reductions exceeding $100,000 within a multi-site tertiary care setting and $1,000,000 within the OLDW would be expected.

CONCLUSION

ESR/CRP co-ordering represents an opportunity to eliminate testing waste and reduce payer costs. A CPOE decision support rule stably reduces ESR/CRP co-ordering rates. Similar results may occur as one component of new commercially available decision support platforms.

Laboratory Utilization and Analytical Validation of Fecal Electrolyte Tests

BACKGROUND

Chronic diarrhea can be categorized as fatty, watery, or inflammatory. Watery diarrhea is further divided into secretory or osmotic types and can be differentiated by measuring fecal electrolytes and osmotic gap. However, with widespread use of endoscopy, it is unclear if these measurements are being used clinically. Furthermore, because stool is not a validated specimen type for Food and Drug Administration-approved electrolyte assays, utilization is a practical concern for laboratories before analytical validation. Here, we determined the clinical utility and validated the performance characteristics of stool electrolytes on the Beckman Coulter AU680.

METHODS

Historical results and literature review were used to determine the clinically relevant ranges for stool electrolytes (Na+, Cl-, K+, phosphate, and Mg2+). Additionally, medical chart review was performed (n = 44 patients) on results to evaluate their clinical utility in chronic diarrhea work-up. Linearity, precision, and stability studies were performed on the AU680. Accuracy was evaluated by comparing results to the Roche Cobas 6000 c501.

RESULTS

For all cases, stool electrolytes and osmotic gap proved valuable in chronic diarrhea work-up. The imprecision of the assays ranged from 0% to 5.9%. All assays were found to be linear within the instrument's analytical measurement range with appropriate slopes and intercepts. The bias between the AU680 and the Roche c501 ranged from -0.48 to 2.39 (mmol/L or mg/dL). Na+, Cl-, and K+ were stable refrigerated for 5 days and up to 1 freeze-thaw cycle. Phosphate and Mg2+ were stable refrigerated for 48 h, but unstable to freeze-thaw cycles.

CONCLUSIONS

Stool osmotic gap is valuable for evaluating chronic diarrhea and can be calculated using electrolyte concentrations measured on the AU680.

Heme-bound SiaA from Streptococcus pyogenes: Effects of mutations and oxidation state on protein stability

The protein SiaA (HtsA) is part of a heme uptake pathway in Streptococcus pyogenes. In this report, we present the heme binding of the alanine mutants of the axial histidine (H229A) and methionine (M79A) ligands, as well as a lysine (K61A) and cysteine (C58A) located near the heme propionates (based on homology modeling) and a control mutant (C47A). pH titrations gave pKa values ranging from 9.0 to 9.5, close to the value of 9.7 for WT SiaA. Resonance Raman spectra of the mutants suggested that the ferric heme environment may be distinct from the wild-type; spectra of the ferrous states were similar. The midpoint reduction potential of the K61A mutant was determined by spectroelectrochemical titration to be 61±3mV vs. SHE, similar to the wild-type protein (68±3mV). The addition of guanidine hydrochloride showed two processes for protein denaturation, consistent with heme loss from protein forms differing by the orientation of the heme in the binding pocket (the half-life for the slower process ranged from less than half a day to two days). The ease of protein unfolding was related to the strength of interaction of the residues with the heme. We hypothesize that kinetically facile but only partial unfolding, followed by a very slow approach to the completely unfolded state, may be a fundamental attribute of heme trafficking proteins. Small motions to release/transfer the heme accompanied by resistance to extensive unfolding may preserve the three dimensional form of the protein for further uptake and release.

Implementation of Clinical Decision Support Rules to Reduce Repeat Measurement of Serum Ionized Calcium, Serum Magnesium, and N-Terminal Pro-B-Type Natriuretic Peptide in Intensive Care Unit Inpatients

BACKGROUND

We assessed the impact of clinical decision support (CDS) rules within the electronic health record for ionized calcium (iCa), serum magnesium (Mg), and N-terminal pro-B-type natriuretic peptide (NT-proBNP) in intensive care unit (ICU) inpatients at a large academic center.

METHODS

A repeat order for measurement of iCa or Mg placed within 24 (iCa) or 48 (Mg) h of a previously nonactionable result, or additional orders for NT-proBNP beyond 1 within a single hospitalization, triggered a CDS pop-up alert showing the prior result and offering the opportunity to cancel the order or to place the order after entering an indication for repeat testing. The number of tests performed for each of these analytes and incidence of adverse clinical outcomes potentially associated with hypocalcemia or hypomagnesemia were compared between the 90-day period before CDS implementation and two 90-day periods immediately following.

RESULTS

iCa test volumes decreased by 48%, Mg by 39%, and NT-proBNP by 28% in the 90-day period immediately following implementation and remained decreased by 54%, 49%, and 22%, respectively, during the following 90-day period (all P values <0.0002). Adverse clinical outcomes potentially associated with hypocalcemia or hypomagnesemia did not increase (all P-values >0.17).

CONCLUSIONS

Implementation of CDS dramatically decreased repeat testing of iCa, Mg, and NT-proBNP without adversely impacting clinical outcomes in the ICU. Expansion of the rules from the ICU units to include the entire hospitalized patient population and expansion to additional analytes is expected to lead to further reductions in testing.

Diagnostic accuracy and clinical relevance of an inflammatory biomarker panel for sepsis in adult critically ill patients

The objective of this study was to assess the diagnostic accuracy of C-reactive protein (CRP), procalcitonin (PCT), and cellular immune markers levels in sepsis. This was a prospective observational study in adult intensive care unit (ICU) patients, between 2012 and 2014. The 8-color flow cytometric biomarker panel included CD64, CD163, and HLA-DR. Index test results were compared with sepsis, using receiver operating characteristic curve analyses. Multivariate logistic regression assessed the relationship of sets of markers with the probability of sepsis. Of 219 enrolled patients, 120 had sepsis. C-statistic was the highest for CRP (0.86) followed by neutrophil CD64 expression (0.83), procalcitonin (0.82), and Acute Physiology and Chronic Health Evaluation (APACHE) IV (0.72). After adjustment for APACHE IV, the combination of CRP, PCT, and neutrophil CD64 measure remained a significant predictor of sepsis with an excellent AUC (0.90). In a targeted ICU population at increased risk of sepsis, CRP, PCT, and neutrophil CD64 combined improve the diagnostic accuracy of sepsis.

Fecal electrolyte testing for evaluation of unexplained diarrhea: Validation of body fluid test accuracy in the absence of a reference method

BACKGROUND

Validation of tests performed on body fluids other than blood or urine can be challenging due to the lack of a reference method to confirm accuracy. The aim of this study was to evaluate alternate assessments of accuracy that laboratories can rely on to validate body fluid tests in the absence of a reference method using the example of sodium (Na(+)), potassium (K(+)), and magnesium (Mg(2+)) testing in stool fluid.

METHODS

Validations of fecal Na(+), K(+), and Mg(2+) were performed on the Roche cobas 6000 c501 (Roche Diagnostics) using residual stool specimens submitted for clinical testing. Spiked recovery, mixing studies, and serial dilutions were performed and % recovery of each analyte was calculated to assess accuracy. Results were confirmed by comparison to a reference method (ICP-OES, PerkinElmer).

RESULTS

Mean recoveries for fecal electrolytes were Na(+) upon spiking=92%, mixing=104%, and dilution=105%; K(+) upon spiking=94%, mixing=96%, and dilution=100%; and Mg(2+) upon spiking=93%, mixing=98%, and dilution=100%. When autoanalyzer results were compared to reference ICP-OES results, Na(+) had a slope=0.94, intercept=4.1, and R(2)=0.99; K(+) had a slope=0.99, intercept=0.7, and R(2)=0.99; and Mg(2+) had a slope=0.91, intercept=-4.6, and R(2)=0.91. Calculated osmotic gap using both methods were highly correlated with slope=0.95, intercept=4.5, and R(2)=0.97. Acid pretreatment increased magnesium recovery from a subset of clinical specimens.

CONCLUSIONS

A combination of mixing, spiking, and dilution recovery experiments are an acceptable surrogate for assessing accuracy in body fluid validations in the absence of a reference method.

Evaluation of Beckman Coulter DxI 800 immunoassay system using clinically oriented performance goals

OBJECTIVES

We evaluated the analytical performance of 24 immunoassays using the Beckman Coulter DxI 800 immunoassay systems at Mayo Clinic, Rochester, MN for trueness, precision, detection limits, linearity, and consistency (across instruments and reagent lots).

METHODS

Clinically oriented performance goals were defined using the following methods: trueness-published desirable accuracy limits, precision-published desirable biologic variation; detection limits - 0.1 percentile of patient test values, linearity - 50% of total error, and consistency-percentage test values crossing key decision points. Local data were collected for precision, linearity, and consistency. Data were provided by Beckman Coulter, Inc. for trueness and detection limits.

RESULTS

All evaluated assays except total thyroxine were within the proposed goals for trueness. Most of the assays met the proposed goals for precision (86% of intra-assay results and 75% of inter-assay results). Five assays had more than 15% of the test results below the minimum detection limits. Carcinoembryonic antigen, total thyroxine and free triiodothyronine exceeded the proposed goals of ±6.3%, ±5% and ±5.7% for dilution linearity. All evaluated assays were within the proposed goals for instrument consistency. Lot-to-lot consistency results for cortisol, ferritin and total thyroxine exceeded the proposed goals of 3.3%, 11.4% and 7% at one medical decision level, while vitamin B12 exceeded the proposed goals of 5.2% and 3.8% at two decision levels.

CONCLUSIONS

The Beckman Coulter DxI 800 immunoassay system meets most of these proposed goals, even though these clinically focused performance goals represent relatively stringent limits.

Analytical performance of three point of care methods for pleural fluid pH analysis

OBJECTIVE

The performance of three point of care methods for pleural fluid pH analysis was compared to a currently validated blood gas analyzer.

DESIGN AND METHODS

An ABL 725 (Radiometer America, Westlake, OH) was used as the reference method to evaluate three cartridge-based assays: ABL 90 FLEX (Radiometer), and i-STAT 1 (Abbott Point of Care, Abbott Park, IL) CG4+ and G3+ cartridges for pleural fluid pH analysis. Pooled residual pleural fluid samples and quality control material were analyzed to determine intra- and inter-assay precision. Method comparison was performed with spiked (n=40) and clinically-ordered (n=10) pleural fluid samples across the analytical measuring range.

RESULTS

All methods demonstrated inter-assay CVs<0.1% at pH values of 7.1 and 7.6, and intra-assay CVs<0.3% at pH values of 7.2 and 7.7. Bland-Altman plots demonstrated clinically significant bias between ABL 725 and each cartridge-based method only at pH>7.6. For samples with pH<7.6 mean bias vs. ABL 725 was -0.01 for ABL 90 FLEX and 0.03 for i-STAT 1 CG4+ and G3+ cartridges. Clinical concordance using a decision limit of pH7.2 was 96-98% for the three methods.

CONCLUSIONS

Analytical and clinical performance of the three cartridge-based methods was comparable to a validated blood gas analyzer for pleural fluid pH analysis. Cartridge-based pH methods offer the advantage of easier troubleshooting for clots and clogs as they use disposable electrodes. However cartridge-based methods are not currently FDA-approved for pleural fluid samples, such that additional validation would be required for this specimen type.

Identification of two heme-binding sites in the cytoplasmic heme-trafficking protein PhuS from Pseudomonas aeruginosa and their relevance to function

PhuS is a cytoplasmic, 39 kDa heme-binding protein from Pseudomonas aeruginosa. It has previously been shown to transfer heme to its cognate heme oxygenase. It is expressed from the phu operon, which encodes a group of proteins known to actively internalize and transport heme from host organisms. This study combines the spectral resolution of resonance Raman spectroscopy with site-directed mutagenesis to identify and characterize the heme-bound states of holo-PhuS. This combined approach has identified a site in monomeric PhuS having alternate His ligands at positions 209 and 212. A second distinct binding site is present in dimeric PhuS. This site supports six-coordinate, low-spin heme, even when both His209 and His212 are mutated to Ala. The presence of conserved His and Tyr residues in all of the homologs characterized to date suggest that the dimer could be of the domain-swapped type in which two protein molecules are cross-linked by bound heme. The multiple heme-bound states and their sensitivity to pH suggest the possibility that these cytoplasmic heme-binding proteins have multiple functions that are toggled by variations in intracellular conditions.

Does background stress heighten or dampen children's cardiovascular responses to acute stress?

OBJECTIVE

Does background stress heighten or dampen children's cardiovascular responses to acute stress?

METHOD

To address this question, the cardiovascular responses to four acute laboratory stressors of 150 children and adolescents were evaluated according to their self-reported background stress level. Background stress was determined during a standardized interview and was a priori classified according to its importance, frequency, and whether it was ongoing or resolved.

RESULTS

Results showed that children and adolescents who reported important stressors or stressors that were ongoing and frequent exhibited a larger increase in diastolic blood pressure and total peripheral resistance during all four laboratory stressors than their low stress counterparts. Additional analysis showed that the results could not be accounted for by sociodemographic variables or by the personality traits measured in this study.

CONCLUSIONS

Results suggest the importance of measuring background stress in understanding an individual's acute stress response.

Familial aggregation of blood pressure and heart rate responses during behavioral stress

Parent-offspring and sibling resemblances in blood pressure and heart rate responses to behavioral stress were evaluated in a sample of 142 families residing in an upper-middle-class community in the Pittsburgh metropolitan area between 1983 and 1985. The sample consisted of 121 daughters and 96 sons ranging in age from 7 to 18 years, and 141 mothers and 119 fathers ranging in age from 31 to 62 years. Three stressors were presented to all participants: serial subtraction, mirror image tracing, and isometric handgrip exercise. Multivariate analyses of the stress responses were based on maximum likelihood estimations of the magnitude of association, which provided collective significance tests, and were adjusted for familial resemblance of resting pressure and heart rate as well as body mass index. These analyses showed significant parent-offspring and sibling associations in resting blood pressure and body mass index, which replicate those found in previous epidemiological investigations. The novel findings in this study were the sibling similarities in heart rate responses to mirror image tracing and in systolic blood pressure responses to isometric handgrip exercise. An analysis of a subset of the sample--only those nonmedicated parents compliant with instructions not to smoke or drink caffeinated or alcoholic beverages for 3 hr prior to testing and their children--showed a parent-offspring resemblance in systolic blood pressure responses to isometric exercise. This analysis, along with the significant sibling association from the full sample, suggests that systolic blood pressure responses to static exercise might aggregate in the family. The results are discussed in light of previous twin data. The relative paucity of significant parent-offspring associations of physiological parameters during serial subtraction and mirror image tracing tasks implies that non-familial influences are most important in determining cardiovascular responses to psychological stress.

The effects of physical activity as maintenance for smoking cessation

The effects of physical activity as a maintenance strategy for smoking cessation were evaluated. After a standard smoking cessation program, forty-two women were randomly assigned to one of three groups that received equal number of maintenance meetings: a physical activity program, smoking habit change information and contact control. Abstinence decreased from 83% at the end of treatment to 73% at 3 months, 49% at six months and 34% at 18 months. No differences were shown in cessation across groups. Group differences were shown for subjective levels of tension-anxiety, those who exercised showed increased tension anxiety levels compared to subjects in the no activity groups.

The effects of nicotine chewing gum on the sensitivity to muscle tension

It has been shown that smoking can alter the sensitivity to muscle activity in female smokers. The present study was designed to assess the effects of smoking cessation and nicotine replacement on sensitivity to muscle tension. Twenty-five women were randomly assigned to one of two groups. One group was given nicotine chewing gum during the withdrawal period and a second group was given no nicotine replacement. Results showed a significant difference in sensitivity at post-test for subjects given nicotine gum compared to subjects receiving no nicotine replacement. These results are consistent with the hypothesis that nicotine alters sensitivity to muscle tension.