Assessment of Circulating Insulin Using Mass Spectrometry During Insulin Glargine Treatment in Type 2 Diabetes: Implications for Estimating Insulin Sensitivity and β-cell Function

AIMS: Given the potential effect of cross-reactivity of insulin glargine U-100 and its metabolites in the insulin immunoassay, we determined the impact on insulin sensitivity and β-cell measures in GRADE participants with type 2 diabetes receiving the analog. MATERIALS AND METHODS: Using liquid chromatography mass spectrometry (LC-MS), we measured concentrations of endogenous insulin, glargine, and its two metabolites (M1 and M2) in fasting and OGTT-stimulated plasma from 19 participants and fasting specimens from another 97 participants 12 months after randomization to receive the insulin glargine. The last dose of glargine was administered before 10:00 pm the night before. Insulin was also measured on these specimens using an immunoassay. We used fasting specimens to calculate insulin sensitivity (HOMA2-S%; QUIKI index, PREDIM index) and β-cell function (HOMA2-B%). Using specimens following glucose ingestion, we calculated insulin sensitivity (Matsuda ISI[comp] index) and β-cell response (insulinogenic index [IGI], and total incremental insulin response [iAUC] / iAUC glucose). RESULTS: In plasma, glargine was metabolized to form the M1 and M2 metabolites that were quantifiable by LC-MS; however, the analog and its metabolites cross-reacted \u3c100% in the insulin immunoassay. This incomplete cross-reactivity resulted in a systematic bias of fasting based measures. In contrast, as M1 and M2 did not change following glucose ingestion, a bias was not observed for IGI and iAUC insulin. CONCLUSIONS: Despite glargine metabolites being detected in the insulin immunoassay, dynamic insulin responses can be used to assess β-cell responsiveness. However, given the cross-reactivity of the glargine metabolites in the insulin immunoassay, fasting-based measures of insulin sensitivity and β-cell function are biased. This article is protected by copyright. All rights reserved

Self-reported Race, Serum Creatinine, Cystatin C, and GFR in Children and Young Adults With Pediatric Kidney Diseases: A Report From the Chronic Kidney Disease in Children (CKiD) Study

Recent reassessment of the use of race in estimated glomerular filtration rate (eGFR) in adults has instigated questions about the role of race in eGFR expressions for children. Little research has examined the associations of self-reported race with measured GFR (mGFR) adjusting for serum creatinine or cystatin C in children and young adults with chronic kidney disease (CKD). This study examined these associations and evaluated the performance of the previously published “U25” (under the age of 25 years) eGFR equations in a large cohort of children and young adults with CKD. Observational cohort study. Participants in the Chronic Kidney Disease in Children (CKiD) study including 190 Black and 675 non-Black participants contributing 473 and 1,897 annual person-visits, respectively. Self- or parental-reported race (Black, non-Black). Adjustment for serum creatinine or cystatin C, body size, and socioeconomic status. mGFR based on iohexol clearance. Linear regression with generalized estimating equations, stratified by age (<6, 6-12, 12-18, and ≥18 years) incorporating serum creatinine or serum cystatin C. Contrasting performance in different self-reported racial groups of the U25 eGFR equations. Self-reported Black race was significantly associated with 12.8% higher mGFR among children in regression models including serum creatinine. Self-reported Black race was significantly associated with 3.5% lower mGFR after adjustment for cystatin C overall but was not significant for those over 12 years. The results were similar after adjustment for body size and socioeconomic factors. The average of creatinine- and cystatin C–based U25 equations was unbiased by self-reported race groups. Small number of children < 6 years; lean body mass was estimated. Differences in the creatinine-mGFR relationship by self-reported race were observed in children and young adults with CKD and were consistent with findings in adults. Smaller and opposite differences were observed for the cystatin C–mGFR relationship, especially in the younger age group. We recommend inclusion of children for future investigations of biomarkers to estimate GFR. Importantly, for GFR estimation among those under 25 years of age, the average of the new U25 creatinine and cystatin C equations without race coefficients yields unbiased estimates of mGFR. [Display omitted

Estimated Kidney Tubular Secretion and Kidney, Cardiovascular, and Mortality Outcomes in CKD: The Systolic Blood Pressure Intervention Trial

Rational &amp; objectiveMany drugs, metabolites, and toxins are cleared by the kidneys via tubular secretion. Whether novel endogenous measures of tubular secretion provide information about kidney, cardiovascular, and mortality risk is uncertain.Study designLongitudinal subgroup analysis of clinical trial participants.Setting &amp; participants2,089 Systolic Blood Pressure Intervention Trial participants with estimated glomerular filtration rate (eGFR)&nbsp;&lt;60 mL/min/1.73 m2 at baseline.ExposureSummary score incorporating urine-to-plasma ratios of 10 endogenous secretion markers measured in paired urine and plasma samples at baseline.OutcomeThe primary outcome was longitudinal change in eGFR. Secondary outcomes included chronic kidney disease (CKD) progression (≥50% eGFR decline or incident kidney failure requiring dialysis or kidney transplantation), a cardiovascular disease (CVD) composite (myocardial infarction, acute coronary syndrome, stroke, acute decompensated heart failure, or death from cardiovascular causes), and mortality.Analytical approachLinear mixed-effect models were used to evaluate the association between the secretion score and change in eGFR, and Cox proportional hazards models were used to evaluate associations with CKD progression, CVD, and mortality.ResultsAt baseline, mean age was 73 ± 9 years and eGFR was 46 ± 11 mL/min/1.73 m2. During a median follow-up of 3.3 years, mean change in eGFR was&nbsp;-1.44% per year, and 72 CKD progression events, 272 CVD events, and 144 deaths occurred. In multivariable analyses, lower secretion score was associated with faster eGFR decline and greater risk of CKD progression, CVD, and mortality. After further adjustment for baseline eGFR and albuminuria, each 1-standard deviation lower secretion score was associated with faster eGFR decline (-0.65% per year; 95% CI,&nbsp;-0.84% to&nbsp;-0.46%), but not CKD progression (HR, 1.23; 95% CI, 0.96-1.58), CVD (HR, 1.02; 95% CI, 0.89-1.18),&nbsp;or mortality (HR, 0.90; 95% CI, 0.74-1.09). The secretion score association with eGFR decline appeared stronger in participants with baseline eGFR&nbsp;&lt;45 mL/min/1.73 m2 (P for interaction &lt;&nbsp;0.001).LimitationsPersons with diabetes and proteinuria &gt;1 g/d were excluded.ConclusionsAmong SPRINT participants with CKD, lower estimated tubular secretion was associated with faster eGFR decline, independent of baseline eGFR and albuminuria, but not with CKD progression, CVD, or mortality

New creatinine- and cystatin C-based equations to estimate GFR without race

Background: Current equations for estimated glomerular filtration rate (eGFR) that use serum creatinine or cystatin C incorporate age, sex, and race to estimate measured GFR. However, race in eGFR equations is a social and not a biologic construct.Methods: We developed new eGFR equations without race using data from two development data sets: 10 studies (8254 participants, 31.5% Black) for serum creatinine and 13 studies (5352 participants, 39.7% Black) for both serum creatinine and cystatin C. In a validation data set of 12 studies (4050 participants, 14.3% Black), we compared the accuracy of new eGFR equations to measured GFR. We projected the prevalence of chronic kidney disease (CKD) and GFR stages in a sample of U.S. adults, using current and new equations.Results: In the validation data set, the current creatinine equation that uses age, sex, and race overestimated measured GFR in Blacks (median, 3.7 ml per minute per 1.73 m2 of body-surface area; 95% confidence interval [CI], 1.8 to 5.4) and to a lesser degree in non-Blacks (median, 0.5 ml per minute per 1.73 m2; 95% CI, 0.0 to 0.9). When the adjustment for Black race was omitted from the current eGFR equation, measured GFR in Blacks was underestimated (median, 7.1 ml per minute per 1.73 m2; 95% CI, 5.9 to 8.8). A new equation using age and sex and omitting race underestimated measured GFR in Blacks (median, 3.6 ml per minute per 1.73 m2; 95% CI, 1.8 to 5.5) and overestimated measured GFR in non-Blacks (median, 3.9 ml per minute per 1.73 m2; 95% CI, 3.4 to 4.4). For all equations, 85% or more of the eGFRs for Blacks and non-Blacks were within 30% of measured GFR. New creatinine-cystatin C equations without race were more accurate than new creatinine equations, with smaller differences between race groups. As compared with the current creatinine equation, the new creatinine equations, but not the new creatinine-cystatin C equations, increased population estimates of CKD prevalence among Blacks and yielded similar or lower prevalence among non-Blacks.Conclusions: New eGFR equations that incorporate creatinine and cystatin C but omit race are more accurate and led to smaller differences between Black participants and non-Black participants than new equations without race with either creatinine or cystatin C alone