Dysbetalipoproteinemia (hyperlipoproteinemia type III, HLP3) is a genetic disorder that results i... more Dysbetalipoproteinemia (hyperlipoproteinemia type III, HLP3) is a genetic disorder that results in the accumulation of cholesterol on highly atherogenic remnant particles. Traditionally, the diagnosis of HLP3 depended upon lipoprotein gel electrophoresis or density gradient ultracentrifugation. Because these two methods are not performed by most clinical laboratories, we describe here two new equations for estimating the cholesterol content of VLDL (VLDL-C), which can then be used for the diagnosis of HLP3. Using results from the beta-quantification (BQ) reference method on a large cohort of dyslipidemic patients (N = 24,713), we identified 115 patients with HLP3 based on having a VLDL-C to plasma TG ratio greater than 0.3 and plasma TG between 150 and 1,000 mg/dl. Next, we developed two new methods for identifying HLP3 and compared them to BQ and a previously described dual lipid apoB ratio method. The first method uses results from the standard lipid panel and the Sampson-NIH equa...
Introduction: Soluble ST2 is a novel prognostic biomarker in adults with chronic heart failure. T... more Introduction: Soluble ST2 is a novel prognostic biomarker in adults with chronic heart failure. The utility of ST2 in pediatric patients with heart failure and other cardiovascular co-morbidities is limited due to lack of normal interpretive values. We sought to determine the reference intervals of ST2 in a healthy pediatric population. Methods: Sera from 240 healthy children were identified from an institutional pediatric biobank at the Mayo Clinic (Rochester, MN). 40 male and 40 female subjects within three age groups (2-6 years, 7-12 years and 13-17 years) were included in the study and those with a diagnosis of anemia, autoimmune disease, hematologic disease/bleeding, circulatory/heart failure, kidney or liver disease, malignancy, malnutrition, diabetes, or pregnancy were excluded. ST2 was measured using a novel high-sensitivity sandwich immunoassay (Presage ST2 assay; Critical Diagnostics, San Diego, CA, USA). Parametric analysis established the 95th percentile reference interval between genders and age groups. Results: ST2 was not significantly associated with age, gender or body mass index (BMI). The median ST2 across the entire cohort was 21 ng/mL (range: 6 - 122 ng/mL). The central 95th percentile was 8 - 64 ng/mL; cut-points for the 90th and 95th percentile were 38 and 48 ng/mL, respectively. Four outliers were excluded due to an ST2 greater than 2 times the interquartile range from the next nearest value. The final central 95th percentile reference interval was 9-50 ng/mL with cut-points for the 90th and 95th percentile at 37 and 43 ng/mL, respectively (median remained 21 ng/mL). Association between ST2 and other diagnoses or medications was not statistically significant. Conclusions: This study determined a normal reference interval for ST2 in pediatric patients without heart failure which aids in effective interpretation of ST2 in a diseased pediatric cohort. The median and upper-limit of normal in pediatric ST2 (21 and 50 ng/mL) were higher than that for adults (19 and 35 ng/mL). Further studies in pediatric cohorts, both normal and diseased, are warranted to evaluate disease-specific trends and clinical decision limits in pediatric heart failure.
Rapid and widespread diagnostic testing is critical to providing timely patient care and reducing... more Rapid and widespread diagnostic testing is critical to providing timely patient care and reducing transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Recently, the Visby Medical COVID-19 point of care (POC) test was granted emergency use authorization (EUA) for qualitative detection of SARS-CoV-2 nucleic acid at the point of care. We evaluated its performance characteristics using residual specimens (n = 100) collected from Mayo Clinic patients using nasopharyngeal (NP) swabs and placed in viral transport media (VTM). The same specimen was tested using both the laboratory reference method (RT-qPCR) and Visby test. The reference methods utilized included a laboratory developed test with EUA (Mayo Clinic Laboratories, Rochester, MN) using the TaqMan assay on a Roche Light Cycler 480 or a commercially available EUA platform (cobas® SARS-CoV-2; Roche Diagnostics, Indianapolis, IN). Positive, negative, and overall percent agreement between the Visby COVID-19 test and the reference method were calculated. Additionally, the limit of detection (LoD) claimed by the manufacturer (1,112 copies/mL) was verified with serial dilutions of heat inactivated virus. The Visby COVID-19 test correctly identified 29/30 positive samples and 69/70 negative samples, resulting in an overall concordance of 98.0%, positive percent agreement of 96.7%, and negative percent agreement of 98.6%. The abbreviated LoD experiment showed that the analytical sensitivity of the method is as low as or lower than 500 copies/mL. Our study demonstrated that Visby COVID-19 is well-suited to address rapid SARS-CoV-2 testing needs. It has high concordance with central laboratory-based RT-qPCR methods, a low rate of invalid results, and superior analytical sensitivity to some other EUA POC devices.
Deficiency of alpha-1 antitrypsin (AAT) is caused by mutations in the SERPINA1 gene that results ... more Deficiency of alpha-1 antitrypsin (AAT) is caused by mutations in the SERPINA1 gene that results in low concentrations of AAT in circulation. The low AAT concentration can result in uninhibited neutrophil elastase activity in the lung, leading to pulmonary tissue damage and lung disease. Clinical evaluation for possible AAT deficiency includes two critical components: measuring AAT concentration in serum and identification of AAT deficiency alleles. In this chapter the methods by which AAT concentration can be measured in the clinical laboratory are described. The two most common methodologies for AAT quantification employ immunometric techniques, specifically nephelometry and turbidimetry, which are both based on light scatter technology. The AAT in the patient sample is combined with an anti-AAT polyclonal antibody solution leading to polymer formation and a proportional amount of subsequent light scatter. Descriptions of each method are presented, and specifics of quality control and assay parameters are discussed. A special discussion focuses on interpretation of results in the context of the different AAT genetic phenotypes and in the context of patients with active inflammatory conditions. Emerging techniques for AAT quantitation by mass spectrometry are also described given that both AAT quantitation and allele identification can be performed on the same assay.
American Journal of Clinical Pathology, Jul 5, 2021
Objectives To evaluate the analytical and clinical performance characteristics of the fifth-gener... more Objectives To evaluate the analytical and clinical performance characteristics of the fifth-generation troponin T reagent. Methods Troponin T was measured in 2,332 paired serum and plasma samples from emergency department and hospital patients using the fourth- and fifth-generation reagents. Testing was repeated after recentrifugation to determine the frequency of analytical outliers and percentage of patients with elevated values for each assay. We conducted separate experiments to determine the effects of biotin and hemolysis interference, as well as measure interinstrument variability, for fifth-generation troponin T. Results Analytic outliers occurred more frequently using the fifth-generation reagent (3.4%) compared with the fourth-generation reagent (1.0%). The frequency of elevated troponin T above the 99th percentile upper reference limit was 26% for the fourth-generation reagent and 52% for the fifth-generation reagent. Clinically significant assay interference by biotin was observed at 20 ng/mL, but hemolysis interference was not observed until an H index of 150. Instrument-to-instrument variability between e411 and e601/602 instrument platforms is predicted to confound clinical interpretation of troponin changes. Conclusions Analytical outliers and instrument-to-instrument variability are the two analytical variables most likely to confound interpretation of changes in fifth-generation troponin T results over time.
BACKGROUND Lipoprotein(a) [Lp(a)] is a pro-atherogenic and pro-thrombotic LDL-like particle recog... more BACKGROUND Lipoprotein(a) [Lp(a)] is a pro-atherogenic and pro-thrombotic LDL-like particle recognized as an independent risk factor for cardiovascular disease (CVD). The cholesterol within Lp(a) (Lp(a)-C) contributes to the reported LDL-cholesterol (LDL-C) concentration by nearly all available methods. Accurate LDL-C measurements are critical for identification of genetic dyslipidemias such as familial hypercholesterolemia (FH). FH risk estimators, such as the Dutch Lipid Clinic Network (DLCN) criteria, utilize LDL-C concentration cut-offs to assess the likelihood of FH. Therefore, failure to adjust for Lp(a)-C can impact accurate FH diagnosis and classification, appropriate follow-up testing and treatments, and interpretation of cholesterol-lowering treatment efficacy. OBJECTIVE In this study, we use direct Lp(a)-C measurements to assess the potential misclassification of FH from contributions of Lp(a)-C to reported LDL-C in patient samples submitted for advanced lipoprotein profiling. METHODS A total of 31,215 samples submitted for lipoprotein profiling were included. LDL-C was measured by beta quantification or calculated by one of three equations. Lp(a)-C was measured by quantitative lipoprotein electrophoresis. DLCN LDL-C cut-offs were applied to LDL-C results before and after accounting for Lp(a)-C contribution. RESULTS Lp(a)-C was detected in 8665 (28%) samples. A total of 940 subjects were reclassified to a lower DLCN LDL-C categories; this represents 3% of the total patient series or 11% of subjects with measurable Lp(a)-C. CONCLUSION Lp(a)-C is present in a significant portion of samples submitted for advanced lipid testing and could cause patient misclassification when using FH diagnostic criteria. These misclassifications could trigger inappropriate follow-up, treatment, and cascade testing for suspected FH.
Purpose of review The success of LDL cholesterol (LDL-C) as a predictor of atherosclerotic cardio... more Purpose of review The success of LDL cholesterol (LDL-C) as a predictor of atherosclerotic cardiovascular disease and a therapeutic target is indisputable. Apolipoprotein B (apoB) is a more contemporary and physiologically relevant measure of atherogenic lipoproteins. This report summarizes recent comparisons of apoB and LDL-C as biomarkers of cardiovascular risk. Recent findings Multiple recent reports have found that LDL-C methods perform poorly at low concentrations (<70 mg/dl). Several meta-analyses from randomized controlled trials and large prospective observational studies have found that apoB and LDL-C provide equivalent information on risk of cardiovascular disease. More innovative analyses have asserted that apoB is a superior indicator of actual risk when apoB and LDL-C disagree. Summary ApoB is more analytically robust and standardized biomarker than LDL-C. Large population studies have found that apoB is at worst clinically equivalent to LDL-C and likely superior when disagreement exists. Realistically, many obstacles prevent the wide spread adoption of apoB and for now providers and their patients must weigh the costs and benefits of apoB.
Dysbetalipoproteinemia (hyperlipoproteinemia type III, HLP3) is a genetic disorder that results i... more Dysbetalipoproteinemia (hyperlipoproteinemia type III, HLP3) is a genetic disorder that results in the accumulation of cholesterol on highly atherogenic remnant particles. Traditionally, the diagnosis of HLP3 depended upon lipoprotein gel electrophoresis or density gradient ultracentrifugation. Because these two methods are not performed by most clinical laboratories, we describe here two new equations for estimating the cholesterol content of VLDL (VLDL-C), which can then be used for the diagnosis of HLP3. Using results from the beta-quantification (BQ) reference method on a large cohort of dyslipidemic patients (N = 24,713), we identified 115 patients with HLP3 based on having a VLDL-C to plasma TG ratio greater than 0.3 and plasma TG between 150 and 1,000 mg/dl. Next, we developed two new methods for identifying HLP3 and compared them to BQ and a previously described dual lipid apoB ratio method. The first method uses results from the standard lipid panel and the Sampson-NIH equa...
Introduction: Soluble ST2 is a novel prognostic biomarker in adults with chronic heart failure. T... more Introduction: Soluble ST2 is a novel prognostic biomarker in adults with chronic heart failure. The utility of ST2 in pediatric patients with heart failure and other cardiovascular co-morbidities is limited due to lack of normal interpretive values. We sought to determine the reference intervals of ST2 in a healthy pediatric population. Methods: Sera from 240 healthy children were identified from an institutional pediatric biobank at the Mayo Clinic (Rochester, MN). 40 male and 40 female subjects within three age groups (2-6 years, 7-12 years and 13-17 years) were included in the study and those with a diagnosis of anemia, autoimmune disease, hematologic disease/bleeding, circulatory/heart failure, kidney or liver disease, malignancy, malnutrition, diabetes, or pregnancy were excluded. ST2 was measured using a novel high-sensitivity sandwich immunoassay (Presage ST2 assay; Critical Diagnostics, San Diego, CA, USA). Parametric analysis established the 95th percentile reference interval between genders and age groups. Results: ST2 was not significantly associated with age, gender or body mass index (BMI). The median ST2 across the entire cohort was 21 ng/mL (range: 6 - 122 ng/mL). The central 95th percentile was 8 - 64 ng/mL; cut-points for the 90th and 95th percentile were 38 and 48 ng/mL, respectively. Four outliers were excluded due to an ST2 greater than 2 times the interquartile range from the next nearest value. The final central 95th percentile reference interval was 9-50 ng/mL with cut-points for the 90th and 95th percentile at 37 and 43 ng/mL, respectively (median remained 21 ng/mL). Association between ST2 and other diagnoses or medications was not statistically significant. Conclusions: This study determined a normal reference interval for ST2 in pediatric patients without heart failure which aids in effective interpretation of ST2 in a diseased pediatric cohort. The median and upper-limit of normal in pediatric ST2 (21 and 50 ng/mL) were higher than that for adults (19 and 35 ng/mL). Further studies in pediatric cohorts, both normal and diseased, are warranted to evaluate disease-specific trends and clinical decision limits in pediatric heart failure.
Rapid and widespread diagnostic testing is critical to providing timely patient care and reducing... more Rapid and widespread diagnostic testing is critical to providing timely patient care and reducing transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Recently, the Visby Medical COVID-19 point of care (POC) test was granted emergency use authorization (EUA) for qualitative detection of SARS-CoV-2 nucleic acid at the point of care. We evaluated its performance characteristics using residual specimens (n = 100) collected from Mayo Clinic patients using nasopharyngeal (NP) swabs and placed in viral transport media (VTM). The same specimen was tested using both the laboratory reference method (RT-qPCR) and Visby test. The reference methods utilized included a laboratory developed test with EUA (Mayo Clinic Laboratories, Rochester, MN) using the TaqMan assay on a Roche Light Cycler 480 or a commercially available EUA platform (cobas® SARS-CoV-2; Roche Diagnostics, Indianapolis, IN). Positive, negative, and overall percent agreement between the Visby COVID-19 test and the reference method were calculated. Additionally, the limit of detection (LoD) claimed by the manufacturer (1,112 copies/mL) was verified with serial dilutions of heat inactivated virus. The Visby COVID-19 test correctly identified 29/30 positive samples and 69/70 negative samples, resulting in an overall concordance of 98.0%, positive percent agreement of 96.7%, and negative percent agreement of 98.6%. The abbreviated LoD experiment showed that the analytical sensitivity of the method is as low as or lower than 500 copies/mL. Our study demonstrated that Visby COVID-19 is well-suited to address rapid SARS-CoV-2 testing needs. It has high concordance with central laboratory-based RT-qPCR methods, a low rate of invalid results, and superior analytical sensitivity to some other EUA POC devices.
Deficiency of alpha-1 antitrypsin (AAT) is caused by mutations in the SERPINA1 gene that results ... more Deficiency of alpha-1 antitrypsin (AAT) is caused by mutations in the SERPINA1 gene that results in low concentrations of AAT in circulation. The low AAT concentration can result in uninhibited neutrophil elastase activity in the lung, leading to pulmonary tissue damage and lung disease. Clinical evaluation for possible AAT deficiency includes two critical components: measuring AAT concentration in serum and identification of AAT deficiency alleles. In this chapter the methods by which AAT concentration can be measured in the clinical laboratory are described. The two most common methodologies for AAT quantification employ immunometric techniques, specifically nephelometry and turbidimetry, which are both based on light scatter technology. The AAT in the patient sample is combined with an anti-AAT polyclonal antibody solution leading to polymer formation and a proportional amount of subsequent light scatter. Descriptions of each method are presented, and specifics of quality control and assay parameters are discussed. A special discussion focuses on interpretation of results in the context of the different AAT genetic phenotypes and in the context of patients with active inflammatory conditions. Emerging techniques for AAT quantitation by mass spectrometry are also described given that both AAT quantitation and allele identification can be performed on the same assay.
American Journal of Clinical Pathology, Jul 5, 2021
Objectives To evaluate the analytical and clinical performance characteristics of the fifth-gener... more Objectives To evaluate the analytical and clinical performance characteristics of the fifth-generation troponin T reagent. Methods Troponin T was measured in 2,332 paired serum and plasma samples from emergency department and hospital patients using the fourth- and fifth-generation reagents. Testing was repeated after recentrifugation to determine the frequency of analytical outliers and percentage of patients with elevated values for each assay. We conducted separate experiments to determine the effects of biotin and hemolysis interference, as well as measure interinstrument variability, for fifth-generation troponin T. Results Analytic outliers occurred more frequently using the fifth-generation reagent (3.4%) compared with the fourth-generation reagent (1.0%). The frequency of elevated troponin T above the 99th percentile upper reference limit was 26% for the fourth-generation reagent and 52% for the fifth-generation reagent. Clinically significant assay interference by biotin was observed at 20 ng/mL, but hemolysis interference was not observed until an H index of 150. Instrument-to-instrument variability between e411 and e601/602 instrument platforms is predicted to confound clinical interpretation of troponin changes. Conclusions Analytical outliers and instrument-to-instrument variability are the two analytical variables most likely to confound interpretation of changes in fifth-generation troponin T results over time.
BACKGROUND Lipoprotein(a) [Lp(a)] is a pro-atherogenic and pro-thrombotic LDL-like particle recog... more BACKGROUND Lipoprotein(a) [Lp(a)] is a pro-atherogenic and pro-thrombotic LDL-like particle recognized as an independent risk factor for cardiovascular disease (CVD). The cholesterol within Lp(a) (Lp(a)-C) contributes to the reported LDL-cholesterol (LDL-C) concentration by nearly all available methods. Accurate LDL-C measurements are critical for identification of genetic dyslipidemias such as familial hypercholesterolemia (FH). FH risk estimators, such as the Dutch Lipid Clinic Network (DLCN) criteria, utilize LDL-C concentration cut-offs to assess the likelihood of FH. Therefore, failure to adjust for Lp(a)-C can impact accurate FH diagnosis and classification, appropriate follow-up testing and treatments, and interpretation of cholesterol-lowering treatment efficacy. OBJECTIVE In this study, we use direct Lp(a)-C measurements to assess the potential misclassification of FH from contributions of Lp(a)-C to reported LDL-C in patient samples submitted for advanced lipoprotein profiling. METHODS A total of 31,215 samples submitted for lipoprotein profiling were included. LDL-C was measured by beta quantification or calculated by one of three equations. Lp(a)-C was measured by quantitative lipoprotein electrophoresis. DLCN LDL-C cut-offs were applied to LDL-C results before and after accounting for Lp(a)-C contribution. RESULTS Lp(a)-C was detected in 8665 (28%) samples. A total of 940 subjects were reclassified to a lower DLCN LDL-C categories; this represents 3% of the total patient series or 11% of subjects with measurable Lp(a)-C. CONCLUSION Lp(a)-C is present in a significant portion of samples submitted for advanced lipid testing and could cause patient misclassification when using FH diagnostic criteria. These misclassifications could trigger inappropriate follow-up, treatment, and cascade testing for suspected FH.
Purpose of review The success of LDL cholesterol (LDL-C) as a predictor of atherosclerotic cardio... more Purpose of review The success of LDL cholesterol (LDL-C) as a predictor of atherosclerotic cardiovascular disease and a therapeutic target is indisputable. Apolipoprotein B (apoB) is a more contemporary and physiologically relevant measure of atherogenic lipoproteins. This report summarizes recent comparisons of apoB and LDL-C as biomarkers of cardiovascular risk. Recent findings Multiple recent reports have found that LDL-C methods perform poorly at low concentrations (<70 mg/dl). Several meta-analyses from randomized controlled trials and large prospective observational studies have found that apoB and LDL-C provide equivalent information on risk of cardiovascular disease. More innovative analyses have asserted that apoB is a superior indicator of actual risk when apoB and LDL-C disagree. Summary ApoB is more analytically robust and standardized biomarker than LDL-C. Large population studies have found that apoB is at worst clinically equivalent to LDL-C and likely superior when disagreement exists. Realistically, many obstacles prevent the wide spread adoption of apoB and for now providers and their patients must weigh the costs and benefits of apoB.
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