Saenger, Amy K.

AbstractBackground: High-sensitivity cardiac troponin assays will augment the frequency of increased results, making important the determination of reference change values to distinguish acute from chronic increases. We assessed short- and long-term biological variability of cardiac troponin T (cTnT) in healthy subjects with a novel high-sensitivity (hs) assay.Methods: We collected blood from 20 healthy volunteers at 5 time points for short-term study and biweekly at 4 times from the same volunteers for long-term study. We analyzed serum samples in duplicate with a hscTnT assay on the Roche Modular E170 and computed reference change values (RCVs) for analytical, intraindividual, interindividual, and total change values (CVA, CVI, CVG, and CVT, respectively) and the index of individuality (II). We calculated RCVs by using a log-normal approach, owing to the skewed results of the data.Results: Short- and long-term CVA values were 53.5% and 98%. CVI and CVG were 48.2% and 85.9%, respectively, for short-term studies and 94% and 94% for long-term studies. Mean δ values for the within-day study were 58% and −57.5%, and between-day mean δ values were 103.4% and −87%. Within- and between-day IIs were 0.8 and 0.14, respectively.Conclusions: The biological variation demonstrated with the hscTnT assay is higher than prior data for cardiac troponin I. This may be attributed to differences in biology or assay imprecision at low concentrations. A short-term change (RCV log normal) of 85% and a long-term change of 315% is necessary to define a changing pattern.

AbstractBackground: Stroke is a devastating condition encompassing a wide range of pathophysiological entities that include thrombosis, hemorrhage, and embolism. Current diagnosis of stroke relies on physician clinical examination and is further supplemented with various neuroimaging techniques. A single set or multiple sets of blood biomarkers that could be used in an acute setting to diagnosis stroke, differentiate between stroke types, or even predict an initial/reoccurring stroke would be extremely valuable.Content: We discuss the current classification, diagnosis, and treatment of stroke, focusing on use of novel biomarkers (either solitary markers or multiple markers within a panel) that have been studied in a variety of clinical settings.Summary: The current diagnosis of stroke remains hampered and delayed due to lack of a suitable mechanism for rapid (ideally point-of-care), accurate, and analytically sensitive biomarker-based testing. There is a clear need for further development and translational research in this area. Potential biomarkers identified need to be transitioned quickly into clinical validation testing for further evaluation in an acute stroke setting; to do so would impact and improve patient outcomes and quality of life.

Abstract Background: Natriuretic peptide concentrations in adults require age- and sex-specific reference intervals for optimal interpretation. Females have higher natriuretic peptide concentrations, and hypotheses suggest that estrogen may be responsible. This study sought to determine the influence of hormone modulation on N-terminal probrain natriuretic peptide (NT-proBNP) by using a pediatric cohort. Children/adolescents typically have rapid hormone changes during puberty, making them an ideal group to study. Methods: We selected 759 specimens (303 male, 456 female; ages 2 months to 18 years, mean 13 years) obtained from the Mayo Clinic Pediatric Residual Specimen Bank. We measured NT-proBNP, sex hormone–binding globulin (SHBG), estradiol, and testosterone by immunoassays or LC-MS/MS and calculated free testosterone. We performed univariate and multivariate analyses to investigate the significance of NT-proBNP with each hormone. Results: Reference values demonstrated a sex difference and sequential age differences in females. Univariate modeling of the hormones with NT-proBNP revealed an independent inverse association of NT-proBNP with testosterone, a direct association with SHBG, and no significant association with estradiol. Multivariate modeling confirmed a strong association of testosterone and SHBG with NT-proBNP. Correlation of hormones with NT-proBNP retained greater significance than either age or sex. Conclusions: In pediatric patients, NT-proBNP is independently associated with both testosterone and SHBG hormone concentrations. Measurements of testosterone are inversely associated with NT-proBNP, and estrogens are marginally associated with NT-proBNP in males but not females, suggesting that androgens and not estrogens modulate sex differences notable in natriuretic peptides. Children and adolescents may require an objective assessment of hormones if optimal interpretation of natriuretic peptide concentrations is desired or the concentrations are confounded. .

Abstract Background: Enzymatic creatinine assays are routinely used in clinical laboratories to provide more accurate estimated glomerular filtration rates and to avoid a perceived lack of analytical specificity associated with picrate (Jaffe) methods. Negative interferences with the enzymatic creatinine assay, which we noted in several patients on dopamine or dobutamine, prompted our further investigation into interference of catecholamines with enzymatic methods. Methods: Spiked solutions of dopamine, dobutamine, epinephrine, and norepinephrine were added to pooled sera at catecholamine concentrations consistent with clinically relevant dosing. Creatinine was measured enzymatically on the Roche P-Modular, Ortho Clinical Diagnostics Vitros 350, and Abbott i-STAT. Jaffe methods were performed on the Roche P-Modular and Siemens Dimension RxL. In 10 patients receiving dopamine and/or dobutamine via a venous or arterial line we evaluated and compared the extent of in vivo creatinine interference in paired serum samples obtained by venipuncture and from indwelling catheters. Results: All catecholamines caused significant negative interference with the Roche enzymatic creatinine assay, most pronounced for dopamine and dobutamine. The Vitros enzymatic assay demonstrated slight negative interferences, and i-STAT enzymatic and Jaffe methods were unaffected by the presence of catecholamines. Significant (P < 0.001) differences in creatinine concentrations by Roche enzymatic vs Jaffe methods were observed in venipuncture specimens compared with arterial or venous catheter specimens, suggesting dopamine and dobutamine reversibly adhere to the catheter lumen. Conclusions: Negative interferences were pronounced for Roche enzymatic results in blood samples obtained from indwelling catheters, a phenomenon not observed in peripheral draws. Physicians and laboratorians should be alert to the possibility of a falsely low creatinine result and reevaluate questionable samples using a method unaffected by catecholamines.

Abstract Background: The International Staging System for multiple myeloma has increased the importance of accurate measurement of serum albumin. Two common albumin assays, bromcresol green (BCG) and agarose gel protein electrophoresis (PEL), frequently yield discordant results, creating confusion regarding which assay is superior for use in myeloma. Methods: We measured albumin by BCG on a Roche Modular system, by PEL with a Helena SPIFE SPE Vis agarose gel, and by immunonephelometry performed on a Dade Behring BNII nephelometer. BCG and PEL were used to measure albumin in 5777 patient samples, and all 3 methods were used in an additional 252 samples. The clinical impact was assessed on 698 myeloma patient samples. Results: For sera with zero/low monoclonal immunoglobulin protein (M)-spike (0 to <15 g/L), results for both BCG and PEL correlated well to nephelometry, although median PEL results were 8 g/L lower than corresponding BCG measurements. Correlation between PEL and nephelometry or BCG diminished with increasing M-spike, with PEL eventually overestimating albumin compared with both other assays. IgG and IgA M-spikes showed significantly different effects on albumin discordance. For 35% of myeloma patients, discrepancy between BCG and PEL had a potentially clinically significant effect on staging, but no difference in group survival was found. Conclusions: Both BCG and PEL correlate well to nephelometry in sera with zero/low M-spikes. In the presence of larger M-spikes, PEL correlates poorly to nephelometry or BCG, whereas BCG compares well with nephelometry regardless of M-spike. Thus, albumin measurement can be performed reliably in myeloma patient sera by use of inexpensive, automated BCG assays.