Assessing bias in GFR estimating equations: improper GFR stratification can yield misleading results.

BACKGROUND: Assessing bias (estimated - measured) is key to evaluating glomerular filtration rate (GFR). Stratification by subgroups can indicate where equations perform differently. However, there is a fallacy in the assessment of two instruments (e.g., eGFR and mGFR) when stratifying on the level of only one of those instruments. Here, we present statistical aspects of the problem and a solution for GFR stratification along with an empirical investigation using data from the CKiD study. METHODS: Compared and contrasted biases (eGFR relative to mGFR) with 95% confidence intervals within strata of mGFR only, eGFR only, and the average of mGFR and eGFR using data from the Chronic Kidney Disease in Children (CKiD) study. RESULTS: A total of 304 participants contributed 843 GFR studies with a mean mGFR of 48.46 (SD = 22.72) and mean eGFR of 48.67 (SD = 22.32) and correlation of 0.904. Despite strong agreement, eGFR significantly overestimated mGFR when mGFR < 30 (+ 6.2%; 95%CI + 2.9%, + 9.7%) and significantly underestimated when mGFR > 90 (-12.2%; 95%CI - 17.3%, - 7.0%). Significant biases in opposite direction were present when stratifying by eGFR only. In contrast, when stratifying by the average of eGFR and mGFR, biases were not significant (+ 1.3% and - 1.0%, respectively) congruent with strong agreement. CONCLUSIONS: Stratifying by either mGFR or eGFR only to assess eGFR biases is ubiquitous but can lead to inappropriate inference due to intrinsic statistical issues that we characterize and empirically illustrate using data from the CKiD study. Using the average of eGFR and mGFR is recommended for valid inferences in evaluations of eGFR biases.

Pharmacokinetics of Human Plasma-Derived Antithrombin in Pediatric Patients Supported on Extracorporeal Membrane Oxygenation.

Extracorporeal membrane oxygenation (ECMO) support of critically ill pediatric patients is associated with increased risk of thromboembolic events, and unfractionated heparin is used commonly for anticoagulation. Given reports of acquired antithrombin (AT) deficiency in this patient population and associated concern for heparin resistance, AT activity measurement and off-label AT replacement have become common in pediatric ECMO centers despite limited optimal dosing regimens. We conducted a retrospective cohort study of pediatric ECMO patients (0 to <18 years) at a single academic center to characterize the pharmacokinetics (PK) of human plasma-derived AT. We demonstrated that a two-compartment turnover model appropriately described the PK of AT, and the parameter estimates for clearance, central volume, intercompartmental clearance, peripheral volume, and basal AT input under non-ECMO conditions were 0.338 dL/h/70 kg, 38.5 dL/70 kg, 1.16 dL/h/70 kg, 40.0 dL/70 kg, and 30.4 units/h/70 kg, respectively. Also, ECMO could reduce bioavailable AT by 50% resulting in 2-fold increase of clearance and volume of distribution. To prevent AT activity from falling below predetermined thresholds of 50% activity in neonates and 80% activity in older infants and children, we proposed potential replacement regimens for each age group, accompanied by therapeutic drug monitoring.

A Drosophila model to screen Alport syndrome COL4A5 variants for their functional pathogenicity.

Alport syndrome is a hereditary chronic kidney disease, attributed to rare pathogenic variants in either of three collagen genes (COL4A3/4/5) with most localized in COL4A5. Trimeric type IV Collagen α3α4α5 is essential for the glomerular basement membrane that forms the kidney filtration barrier. A means to functionally assess the many candidate variants and determine pathogenicity is urgently needed. We used Drosophila, an established model for kidney disease, and identify Col4a1 as the functional homolog of human COL4A5 in the fly nephrocyte (equivalent of human podocyte). Fly nephrocytes deficient for Col4a1 showed an irregular and thickened basement membrane and significantly reduced nephrocyte filtration function. This phenotype was restored by expressing human reference (wildtype) COL4A5, but not by COL4A5 carrying any of three established pathogenic patient-derived variants. We then screened seven additional patient COL4A5 variants; their ClinVar classification was either likely pathogenic or of uncertain significance. The findings support pathogenicity for four of these variants; the three others were found benign. Thus, demonstrating the effectiveness of this Drosophila in vivo kidney platform in providing the urgently needed variant-level functional validation.

Higher levels of brain injury biomarker tau are associated with unfavorable outcomes in patients supported with ECMO following cardiac arrest.

Aim: We sought to determine if higher plasma levels of brain injury biomarkers neurofilament light (NfL), phosphorylated tau 181 (pT181), tau, and ubiquitin C-terminal hydrolase L1 (UCHL1) were associated with unfavorable outcomes in children supported on extracorporeal membrane oxygenation (ECMO) with and without preceding cardiac arrest. Methods: We conducted a secondary analysis of a two-center prospective observational study of ECMO patients 0-<18 years. Plasma concentrations of NfL, pT181, tau, and UCHL1 were measured on ECMO days 1, 2 and 3. Unfavorable outcome was defined as in-hospital mortality or discharge Pediatric Cerebral Performance Category (PCPC) >2 with decline from baseline PCPC among survivors. Results: Among 88 children on ECMO, mean tau levels were significantly higher on each of the first three ECMO days in children who underwent extracorporeal cardiopulmonary resuscitation (ECPR) compared to those with non-ECPR cardiac arrest or with no cardiac arrest preceding ECMO. Higher ECMO day 1 tau levels were significantly associated with increased hazard of unfavorable outcome in unadjusted (HR, 1.35, 95% CI 1.09-1.66) and adjusted (HR, 1.42; 95% CI 1.13-1.79) models. Higher levels of NfL or pT181 were not associated with increased hazard for unfavorable outcome in multivariable models. UCHL1 values were outside of detectable limits and thus deferred from analysis. Conclusions: Levels of tau were significantly associated with increased hazard of death or unfavorable neurologic outcome in unadjusted and adjusted models. Biomarkers of brain injury, particularly tau, may aid in detection of neurologic injury and neuroprognostication in patients on ECMO with and without preceding cardiac arrest.

Exploratory factor analysis yields grouping of brain injury biomarkers significantly associated with outcomes in neonatal and pediatric ECMO.

In this two-center prospective cohort study of children on ECMO, we assessed a panel of plasma brain injury biomarkers using exploratory factor analysis (EFA) to evaluate their interplay and association with outcomes. Biomarker concentrations were measured daily for the first 3 days of ECMO support in 95 participants. Unfavorable composite outcome was defined as in-hospital mortality or discharge Pediatric Cerebral Performance Category > 2 with decline ≥ 1 point from baseline. EFA grouped 11 biomarkers into three factors. Factor 1 comprised markers of cellular brain injury (NSE, BDNF, GFAP, S100ß, MCP1, VILIP-1, neurogranin); Factor 2 comprised markers related to vascular processes (vWF, PDGFRß, NPTX1); and Factor 3 comprised the BDNF/MMP-9 cellular pathway. Multivariable logistic models demonstrated that higher Factor 1 and 2 scores were associated with higher odds of unfavorable outcome (adjusted OR 2.88 [1.61, 5.66] and 1.89 [1.12, 3.43], respectively). Conversely, higher Factor 3 scores were associated with lower odds of unfavorable outcome (adjusted OR 0.54 [0.31, 0.88]), which is biologically plausible given the role of BDNF in neuroplasticity. Application of EFA on plasma brain injury biomarkers in children on ECMO yielded grouping of biomarkers into three factors that were significantly associated with unfavorable outcome, suggesting future potential as prognostic instruments.

Incidence of non-AIDS defining comorbidities among young adults with perinatally acquired HIV in North America.

OBJECTIVE: The aim of this study is to describe the incidence of diabetes mellitus type 2 (T2DM), hypercholesterolemia, hypertriglyceridemia, hypertension, and chronic kidney disease (CKD) from 2000 to 2019 among North American adults with perinatally acquired HIV (PHIV) aged 18-30 years. DESIGN: Description of outcomes based on electronic health records for a cohort of 375 young adults with PHIV enrolled in routine HIV care at clinics contributing data to the North American AIDS Cohort Collaboration on Research and Design (NA-ACCORD). METHODS: We estimated overall, sex, and race-stratified cumulative incidences using Turnbull estimation, and incidence rates using quasi-Poisson regression. T2DM was defined as glycosylated hemoglobin more than 6.5% or based on clinical diagnosis and medication use. Hypercholesterolemia was based on medication use or total cholesterol at least 200 mg/dl. Hypertriglyceridemia was based on medication use or fasting triglyceride at least 150 mg/dl or nonfasting at least 200 mg/dl. Hypertension was based on clinical diagnosis. CKD was defined as estimated glomerular filtration rates less than 90 ml/mi|1.73 m 2 for at least 3 months. RESULTS: Cumulative incidence by age 30 and incidence rates from age 18 to 30 (per 100 person-years) were T2DM: 19%, 2.9; hypercholesterolemia: 40%, 4.6; hypertriglyceridemia: 50%, 5.6; hypertension: 22%, 2.0; and CKD: 25%, 3.3. Non-Black women had the highest incidence of hypercholesterolemia and hypertriglyceridemia, Black adults had the highest hypertension incidence, and Black men had the highest CKD incidence. CONCLUSION: There was a high incidence of five chronic comorbidities among people with PHIV. Earlier screening at younger ages might be considered for this unique population to strengthen prevention strategies and initiate treatment in a timely way.