Shannon Haymond

Conductive diamond thin-films in electrochemistry

Diamond electrodes offer superb properties for a variety of electrochemical technologies, properties that include: corrosion resistance, low background current, good responsiveness without pretreatment, resistance to fouling, and optical transparency. Electroanalysis, electrocatalysis, spectroelectrochemistry, and bioelectrochemistry are areas of electrochemistry in which diamond thin-films, both microcrystalline and nanocrystalline, are being successfully researched. A brief review is given herein of some of our R&D efforts in each of these areas.

Predictive power of serum cystatin C to detect acute kidney injury and pediatric-modified RIFLE class in children undergoing cardiac surgery

Objective: Acute kidney injury is a frequent and serious complication of cardiopulmonary bypass. In current clinical practice, serum creatinine is used to detect acute kidney injury. Cystatin C is a novel biomarker for kidney function that has been shown to be superior to serum creatinine in predicting acute kidney injury in adults after cardiopulmonary bypass. The aim of this study was to determine whether early cystatin C levels predict acute kidney injury associated with cardiopulmonary bypass in pediatric patients undergoing cardiac surgery and if cystatin C could predict pediatric-modified RIFLE (Risk, Injury, Failure, Loss, End-stage kidney disease) class and renal injury as determined by estimated glomerular filtration rate. We also investigated whether ultrafiltration during cardiopulmonary bypass affects cystatin C levels. Design: Prospective, observational cohort study. Setting: Cardiac intensive care unit in a tertiary, academic pediatric hospital. Patients: One hundred pediatric patients who underwent cardiac surgery involving cardiopulmonary bypass. Interventions: None. Measurements and Main Results: Acute kidney injury was defined as a 50% increase in serum creatinine from a preoperative baseline anytime through postoperative day 4. Severity of acute kidney injury was determined by pediatric RIFLE class using estimated glomerular filtration rate criteria only. Renal injury was also determined by an absolute estimated glomerular filtration rate <80 mL/min/1.73 m2. Cystatin C levels were measured before and after ultrafiltration. Twenty-eight patients (28%) developed acute kidney injury. Cystatin C predicted acute kidney injury as early as 8 hrs after surgery. When applying pediatric RIFLE criteria to the entire study, 30 patients reached “risk” and five developed “injury.” Cystatin C was a good predictor of the development of “injury” (under the receiver operating characteristic curve, 0.834–0.875) and of renal injury by estimated glomerular filtration rate (under the receiver operating characteristic curve, 0.717–0.835) (all p < .05). Cystatin C levels decreased perioperatively and correlated with volume of fluid removed by ultrafiltration. Conclusions: Cystatin C is an early predictor of acute kidney injury in children after cardiopulmonary bypass. Cystatin C is a good predictor of pediatric RIFLE classification and of decreased estimated glomerular filtration rate after cardiopulmonary bypass. Serum cystatin C may be cleared by ultrafiltration.

A Direct Comparison Between Lamellar Body Counts and Fluorescent Polarization Methods for Predicting Respiratory Distress Syndrome

Our objective was to directly compare the diagnostic usefulness of lamellar body counting (LBC) and the TDx-FLM II assay (Abbott Laboratories, Abbott Park, IL) for predicting respiratory distress syndrome (RDS). This was a 5-year, retrospective, cohort study. A diagnosis of RDS was given to infants who received surfactant treatment and/or required ventilator support and/or continuous positive airway pressure for more than 24 hours. There were 172 infants without RDS and 12 with RDS included in the study. By using a TDx-FLM II cutoff of 55 mg/g or more for maturity, the sensitivity was 83%, specificity was 65%, predictive value of a mature result was 98%, and predictive value of an immature result was 14%. These results were similar to LBC using a cutoff of 50,000/microL or more with sensitivity of 92%, a specificity of 60%, a predictive value of a mature result of 99%, and a predictive value of an immature result of 14%. The LBC and TDx-FLM II methods have similar clinical usefulness.

Applicability of estimating glomerular filtration rate equations in pediatric patients: comparison with a measured glomerular filtration rate by iohexol clearance.

Estimating glomerular filtration rate (eGFR) has become popular in clinical medicine as an alternative to measured GFR (mGFR), but there are few studies comparing them in clinical practice. We determined mGFR by iohexol clearance in 81 consecutive children in routine practice and calculated eGFR from 14 standard equations using serum creatinine, cystatin C, and urea nitrogen that were collected at the time of the mGFR procedure. Nonparametric Wilcoxon test, Spearman correlation, Bland-Altman analysis, bias (median difference), and accuracy (P15, P30) were used to compare mGFR with eGFR. For the entire study group, the mGFR was 77.9 ± 38.8 mL/min/1.73 m(2). Eight of the 14 estimating equations demonstrated values without a significant difference from the mGFR value and demonstrated a lower bias in Bland-Altman analysis. Three of these 8 equations based on a combination of creatinine and cystatin C (Schwartz et al. New equations to estimate GFR in children with CKD. J Am Soc Nephrol 2009;20:629-37; Schwartz et al. Improved equations estimating GFR in children with chronic kidney disease using an immunonephelometric determination of cystatin C. Kidney Int 2012;82:445-53; Chehade et al. New combined serum creatinine and cystatin C quadratic formula for GFR assessment in children. Clin J Am Soc Nephrol 2014;9:54-63) had the highest accuracy with approximately 60% of P15 and 80% of P30. In 10 patients with a single kidney, 7 with kidney transplant, and 11 additional children with short stature, values of the 3 equations had low bias and no significant difference when compared with mGFR. In conclusion, the 3 equations that used cystatin C, creatinine, and growth parameters performed in a superior manner over univariate equations based on either creatinine or cystatin C and also had good applicability in specific pediatric patients with single kidneys, those with a kidney transplant, and short stature. Thus, we suggest that eGFR calculations in pediatric clinical practice use only a multivariate equation.

Metabolic alterations in children with obstructive sleep apnea

IMPORTANCE The incidence of obesity is rising in the United States and has been linked to Obstructive Sleep Apnea (OSA) even in young children. Understanding the role that obesity and OSA play in alterations in metabolic variables that can lead to serious health issues is essential to the care and counseling of affected children. OBJECTIVES To evaluate the association of alterations in metabolic variables, including insulin resistance, to OSA in young, obese children. DESIGN Retrospective, case-control series. SETTING Tertiary care childrens hospital. PARTICIPANTS Obese children aged 2-12 years who had undergone overnight polysomography and routine laboratory testing for lipid levels, fasting glucose, and insulin from January 1, 2006 to December 31, 2012 were identified from a TransMed Bio-Integration Suite and Epics clarity database search. RESULTS A total of 76 patients were included for analysis. Forty-three (56.6%) were male, and the mean age was 8.3±2.5 years (range, 2.4-11.9 years). The mean body mass index (BMI) z score was 2.8±0.75 (range, 1.7-6.3), and all patients were obese (BMI z score>95th percentile). Twenty two patients (28.9%) had an apnea-hypopnea index (AHI) <1/h (no OSA), 27 (35.5%) an AHI≥1<5/h, 12 (15.8%) had an AHI ≥5<9.99/h, and 15 (19.7%) had an AHI≥10/h. There was no significant difference in total cholesterol, triglycerides, high and low density lipoprotein levels, systolic and diastolic blood pressure in those patients with or without OSA. Fasting insulin, blood glucose, and homeostasis model assessment (HOMA) were significantly higher in patients with OSA compared to those with no OSA (p<0.01). AHI correlated to alterations in insulin as well as glucose homeostasis on multivariate analysis. Results from logistic regression analysis showed that fasting insulin (p<0.01), and HOMA (p<0.01) predicted severe OSA independent of age, gender, and BMI z score in these patients. CONCLUSION Metabolic alterations in glucose and insulin levels, known to be associated with obesity and increased risk for cardiovascular disease, appear to relate to the severity of OSA in young children.

Evaluation of Asymmetric Dimethylarginine, Arginine, and Carnitine Metabolism in Pediatric Sepsis

Objective: Increased plasma concentrations of the endogenous nitric oxide synthase inhibitor, asymmetric dimethylarginine, decreased arginine bioavailability, and mitochondrial dysfunction have been reported in adult sepsis. We studied whether asymmetric dimethylarginine, arginine, and carnitine metabolism (a measure of mitochondrial dysfunction) are altered in pediatric sepsis and whether these are clinically useful biomarkers. Design: Prospective, observational study. Setting: Pediatric intensive care unit at an academic medical center. Patients: Ninety patients ⩽18 yrs old, 30 with severe sepsis or septic shock, compared with 30 age-matched febrile and 30 age-matched healthy control subjects. Interventions: None. Measurements and Main Results: Plasma asymmetric dimethylarginine and whole blood arginine, citrulline, ornithine, and acylcarnitine:free carnitine ratio were measured daily for septic patients and once for control subjects using tandem mass spectrometry. Plasma asymmetric dimethylarginine concentration (median; interquartile range µmol/L) on day 1 was lower in severe sepsis and septic shock (0.38; 0.30–0.56) compared with febrile (0.45; 0.40–0.59) and healthy (0.60; 0.54–0.67) control subjects (p < .001), although decreased asymmetric dimethylarginine was predominantly found in neutropenic patients. Day 1 arginine was lower in septic (10; interquartile range, 7–20 µmol/L) compared with healthy patients (32; interquartile range, 23–40; p < .001), and the arginine:ornithine ratio was decreased in sepsis, indicating increased arginase activity (an alternative pathway for arginine metabolism). The arginine:asymmetric dimethylarginine and acylcarnitine:free carnitine ratios did not differ between septic and control patients. Asymmetric dimethylarginine was inversely correlated with organ dysfunction by Pediatric Logistic Organ Dysfunction score (r = −0.50, p = .009), interleukin-6 (r = −0.55, p = .01), and interleukin-8 (r = −0.52, p = .03) on admission. Arginine, arginine:asymmetric dimethylarginine, and acylcarnitine:free carnitine were not associated with organ dysfunction or outcomes. Conclusions: Asymmetric dimethylarginine was decreased in pediatric sepsis and was inversely associated with inflammation and organ dysfunction. This suggests that inhibition of nitric oxide synthase by asymmetric dimethylarginine accumulation is unlikely to impact sepsis pathophysiology in septic children despite decreased arginine bioavailability. We did not find an association of asymmetric dimethylarginine with altered carnitine metabolism nor were asymmetric dimethylarginine, arginine, and acylcarnitine:free carnitine useful as clinical biomarkers.

Measuring Estrogen Exposure and Metabolism: Workshop Recommendations on Clinical Issues.

Departments of Pathology and Medicine (L.M.D.), Pennsylvania State University School of Medicine,Hershey, Pennsylvania 17003; Division of Biostatistics and Epidemiology (S.E.H.), University ofMassachusetts, Amherst, Massachusetts 01003; Ann and Robert H. Lurie Children’s Hospital of Chicago(S.H.), Chicago, Illinois 60611; Nuffield Department of Population Health (T.K.), University of Oxford,Oxford OX3 7LF, United Kingdom; Department of Medicine (W.R.), Columbia University, College ofPhysicians and Surgeons, New York, New York 10032; Division of Endocrinology and Metabolism(R.J.S.), University of Virginia Health Sciences System, Charlottesville, Virginia 22903; Departments ofObstetrics/Gynecology and Preventive Medicine (F.Z.S.), University of Southern California Keck School ofMedicine, Los Angeles, California 90033; Division of Laboratory Sciences (H.W.V.), Centers for DiseaseControl and Prevention, Atlanta, Georgia 30333; and Division of Cancer Epidemiology and Genetics(R.G.Z.), National Cancer Institute, Bethesda, Maryland 20892

Pilot Study of the Association of the DDAH2 −449G Polymorphism with Asymmetric Dimethylarginine and Hemodynamic Shock in Pediatric Sepsis

Background Genetic variability in the regulation of the nitric oxide (NO) pathway may influence hemodynamic changes in pediatric sepsis. We sought to determine whether functional polymorphisms in DDAH2, which metabolizes the NO synthase inhibitor asymmetric dimethylarginine (ADMA), are associated with susceptibility to sepsis, plasma ADMA, distinct hemodynamic states, and vasopressor requirements in pediatric septic shock. Methodology/Principal Findings In a prospective study, blood and buccal swabs were obtained from 82 patients ≤18 years (29 with severe sepsis/septic shock plus 27 febrile and 26 healthy controls). Plasma ADMA was measured using tandem mass spectrometry. DDAH2 gene was partially sequenced to determine the −871 6g/7g insertion/deletion and −449G/C single nucleotide polymorphisms. Shock type (“warm” versus “cold”) was characterized by clinical assessment. The −871 7g allele was more common in septic (17%) then febrile (4%) and healthy (8%) patients, though this was not significant after controlling for sex and race (p = 0.96). ADMA did not differ between −871 6g/7g genotypes. While genotype frequencies also did not vary between groups for the −449G/C SNP (p = 0.75), septic patients with at least one −449G allele had lower ADMA (median, IQR 0.36, 0.30–0.41 µmol/L) than patients with the −449CC genotype (0.55, 0.49–0.64 µmol/L, p = 0.008) and exhibited a higher incidence of “cold” shock (45% versus 0%, p = 0.01). However, after controlling for race, the association with shock type became non-significant (p = 0.32). Neither polymorphism was associated with inotrope score or vasoactive infusion duration. Conclusions/Significance The −449G polymorphism in the DDAH2 gene was associated with both low plasma ADMA and an increased likelihood of presenting with “cold” shock in pediatric sepsis, but not with vasopressor requirement. Race, however, was an important confounder. These results support and justify the need for larger studies in racially homogenous populations to further examine whether genotypic differences in NO metabolism contribute to phenotypic variability in sepsis pathophysiology.

Utilization of cardiac troponin assays in adult and pediatric populations: Guideline recommendations vs. reality.

OBJECTIVES We hypothesized significant gaps remained for cardiac troponin (cTn) utilization in the United States, despite an emerging evidence base and guideline recommendations. We tested this hypothesis and investigated differences and trends between the use of cTn in adult versus pediatric hospitals. DESIGN AND METHODS Individuals were identified by a targeted distribution through personal contact and professional society email lists. Participants completed an online survey (Qualtrics) from 07/15/13 to 07/26/13. The 31-item questionnaire used skipped logic and collected data about the respondent and their institutional cTn clinical practices. Data tabulation and analysis were conducted using Qualtrics and Microsoft Excel. RESULTS A total of 159 unique laboratories responded to the survey, representing primarily adult (81%) versus pediatric (19%) institutions. 59% of laboratories utilize the guideline recommended 99th percentile as the upper reference limit (URL) for cTn, with large variability in reporting practices among users of the same assay. 73% of laboratories reported simultaneous ordering of other cardiac biomarkers with cTn, a majority which included CK-MB. Interpretive comments were used with cTn in 71 laboratories with a significant amount of heterogeneity. Pediatric hospitals reported a lower frequency of cTn orders and were less likely to consider elevated cTn a critical value. CONCLUSIONS Gaps in current utilization and reporting of cTn exist, along with practices inconsistent with clinical guideline recommendations. Implementation of the 99th percentile and serial sampling protocols will be critical to adoption of high-sensitivity cTn assays. Differences in chest pain etiology are the most likely reason for the notable differences between cTn use in adults versus pediatric hospitals.

Determination of iohexol in human serum by a semi-automated liquid chromatography tandem mass spectrometry method.

OBJECTIVES Measured glomerular filtration rate (mGFR) is the best indicator of renal function in children and adolescents. GFR determination using iohexol clearance has been increasingly accepted and applied in clinical practice because it is accurate, readily available, non-radioactive, safe and is used intravenously even in the presence of renal disease. This study describes the development and evaluation of a semi-automated method for determination of iohexol in human serum using liquid chromatography coupled with electrospray ionization (ESI) tandem mass spectrometry (LC-MS/MS). DESIGN AND METHODS Iohexol was extracted from serum using a MICROLAB® NIMBUS4 automation robot and supernatant was dried under nitrogen gas and reconstituted in mobile phase. Ioversol was used as the internal standard. Chromatography was performed using a C-8 analytical column (Phenomenex, 3 μm, 50 × 3.0 mm I.D.) at room temperature and a gradient LC method on a Waters 2795 Alliance HT HPLC system. The flow rate was 0.5 mL/min and the retention times were 2.36 min and 2.14 min for iohexol and ioversol, respectively. Detection by MS/MS was achieved using a (Micromass Quattro Micro) tandem mass spectrometer operated in the ESI-positive mode. The multiple-reaction monitoring (MRM) method used ion transitions m/z 821.9 to 803.7 for iohexol and m/z 807.9 to 588.7 for ioversol. Method validation studies were conducted to determine the linearity, accuracy, precision, matrix effects and stability. A method comparison of blinded, residual patient samples was conducted with a well-established method. RESULTS The method was linear from 7.7 μg/mL to 2000.0 μg/mL. The low limit of quantification and the detection limit were established at 7.7 and 3.0 μg/mL, respectively. Within-run and between-run precisions were found to be <6% CV and measured values deviated no more than 5% from target concentrations. Carryover and matrix effects were not significant. Comparison to a well-established method showed very good agreement with correlation coefficient of 0.996 for iohexol and 0.993 for GFR/1.73 m(2). CONCLUSIONS This method accurately and precisely quantifies iohexol in 50 μL of serum, enabling determination of mGFR by iohexol clearance. The method is highly correlated to a reference method. Use of an automated liquid handler reduces labor-intensive, manual sample preparation steps. The stability of this analyte and the robustness of this assay fit well within our clinical workflow and we have successfully applied this method to determine mGFR in pediatric patients.