Estimation of Insulin Resistance in Mexican Adults by the [(13)C]Glucose Breath Test Corrected for Endogenous Total CO(2) Production

Accuracy of the 13C-glucose breath test to identify insulin resistance in non-diabetic adults

AIMS

To assess the validity of the ¹³C-glucose breath test (¹³C-GBT) to identify insulin resistance (IR) in non-diabetic individuals, using hyperinsulinemic-euglycemic clamps as gold standard. This validity was compared with that of other IR surrogates.

METHODOLOGY

Non-diabetic adults were studied in a cross-sectional design. In a first appointment, oral glucose tolerance tests were conducted simultaneously with ¹³C-GBTs. Oral 75 g glucose dissolved in 150 ml water, followed by 1.5 mg/Kg body weight U-¹³C-glucose dissolved in 50 ml water, was administered. Breath and blood samples were collected at baseline and at 30-min intervals. The percentages of glucose-oxidized dose at given periods were calculated. Clamps were conducted a week later. A clamp-derived M value ≤ 6.0 mg/kg*min was used as cut-off. ROC curves were constructed for ¹³C-GBT, fasting insulin, HOMA, and ISI-composite.

RESULTS

Thirty-eight subjects completed the study protocol. The correlation coefficient between the ¹³C-GBT derived glucose-oxidized dose at 180 min and M values was 0.524 (p = 0.001). The optimal value to identify IR with the ¹³C-GBT was 4.23% (AUC 0.81; ₉₅CI 0.66, 0.96; accuracy 0.82, ₉₅CI 0.66, 0.92). The ¹³C-GBT sensitivity (0.88) was higher than HOMA and fasting insulin sensitivities (0.83 and 0.75 respectively), while their specificities were comparable (0.71, 0.71, and 0.79, respectively). The sensitivity of ISI-C was higher (0.92) than that of the ¹³C-GBT, but its specificity was poor (0.36). The accuracy of the ¹³C-GBT was superior to that of the other studied surrogates.

CONCLUSIONS

The ¹³C-GBT is a valid and accurate method to detect IR in non-diabetic adults. Therefore, it is potentially useful in clinical and community settings.

Validity and reliability of a novel metabolic flexibility test in children with obesity

Existing methods for diagnosing diabetes and for identifying risk of diabetes development are completed under resting conditions and based on adult data. Studying additional methods to identify metabolic risk in children is warranted. Our objective was to examine the validity and reliability of a metabolic flexibility (MetFlex) test for screening glycemia and insulin resistance (IR) in children. We hypothesized higher MetFlex during exercise would be correlated with lower fasting glucose and homeostasis model assessment of insulin resistance (HOMA-IR) and higher whole body insulin sensitivity index (WBISI) and insulin secretion-sensitivity index-2 (ISSI-2). Thirty-four children with obesity (14 boys, 20 girls) attended two visits. At visit 1, an oral glucose tolerance test (OGTT) was followed by anthropometric and aerobic fitness (V̇o_2max) assessments. Insulin and glucose during the OGTT were used to calculate HOMA-IR, WBISI, and ISSI-2. At visit 2, a ¹³C-enriched carbohydrate drink was ingested before 60 min of exercise at 45% V̇o_2max. Breath measurements were collected to calculate area under the curve exogenous carbohydrate to measure MetFlex. Pearson's r correlation showed no significant association between MetFlex during exercise with fasting glucose ( r = -0.288, P = 0.110). MetFlex was associated with log-HOMA-IR ( r = -0.597, P = 0.024), log-WBISI ( r = 0.575, P = 0.051), and log-ISSI-2 ( r = 0.605, P = 0.037) in boys but not girls. When repeated ( n = 18), MetFlex was deemed a reliable test (intraclass correlation coefficient = 0.692). MetFlex during exercise was negatively associated with IR and β-cell function in boys. Further research is required to explore clinical utility of the MetFlex test and explain the lack of association in girls. NEW & NOTEWORTHY This study is the first to investigate the validity and reliability of a novel noninvasive metabolic flexibility (MetFlex) test for identifying insulin resistance in children with obesity. MetFlex was measured during exercise using [¹³C]glucose stable isotope methodology. Findings showed that MetFlex was negatively associated with insulin resistance in boys but not in girls with obesity. Future work is required to investigate these sex differences. MetFlex test results were deemed reliable when repeated on a separate day.

13C isotopic abundances in natural nutrients: a newly formulated test meal for non-invasive diagnosis of type 2 diabetes

A new method to replace commercially prepared ¹³C-labelled glucose with naturally available ¹³C-enriched substrates could result in promotion of the clinical applicability of the isotopic breath test for detection of type 2 diabetes (T2D). Variation of the carbon-13 isotope in human breath depends on the ¹³C enrichment in the diet taken by subjects. Here, we formulated a new test meal comprising naturally available ¹³C-enriched foods and subsequently administered it to non-diabetic control (NDC) subjects and those with T2D. We found that the new test meal-derived ¹³C enrichment of breath CO₂ was significantly lower in T2D compared with NDC. Furthermore, from our observations T2D exhibited higher isotopic enrichment of oxygen-18 (¹⁸O) in breath CO₂ compared with NDC following ingestion of the new meal. We determined the optimal diagnostic cut-off values of ¹³C (i.e. δ ¹³C‰ = 7.5‰) and ¹⁸O (i.e. δ ¹⁸O‰ = 3.5‰) isotopes in breath CO₂ for precise classification of T2D and NDC. Our new method involving the administration of naturally ¹³C-abundant nutrients showed a typical diagnostic sensitivity and specificity of about 95%, suggesting a valid and potentially robust global method devoid of any synthetically manufactured commercial ¹³C-enriched glucose which thus may serve as an alternative diagnostic tool for routine clinical applications.

The 13C-Glucose Breath Test for Insulin Resistance Assessment in Adolescents: Comparison with Fasting and Post-Glucose Stimulus Surrogate Markers of Insulin Resistance

OBJECTIVE

To evaluate the use of the 13C-glucose breath test (13C-GBT) for insulin resistance (IR) detection in adolescents through comparison with fasting and post-glucose stimulus surrogates.

METHODS

One hundred thirty-three adolescents aged between 10 and 16 years received an oral glucose load of 1.75 g per kg of body weight dissolved in 150 mL of water followed by an oral dose of 1.5 mg/kg of U-13C-Glucose, without a specific maximum dose. Blood samples were drawn at baseline and 120 minutes, while breath samples were obtained at baseline and at 30, 60, 90, 120, 150, and 180 minutes. The 13C-GBT was compared to homeostasis model assessment (HOMA) IR (≥p95 adjusted by gender and age), fasting plasma insulin (≥p90 adjusted by gender and Tanner stage), results of 2-h oral glucose tolerance test (OGTT), insulin levels (≥65 μU/mL) in order to determine the optimal cut-off point for IR diagnosis.

RESULTS

13C-GBT data, expressed as adjusted cumulative percentage of oxidized dose (A% OD), correlated inversely with fasting and post-load IR surrogates. Sexual development alters A% OD results, therefore individuals were stratified into pubescent and post-pubescent. The optimal cut-off point for the 13C-GBT in pubescent individuals was 16.3% (sensitivity=82.8% & specificity=60.6%) and 13.0% in post-pubescents (sensitivity=87.5% & specificity=63.6%), when compared to fasting plasma insulin. Similar results were observed against HOMA and 2-h OGTT insulin.

CONCLUSION

The 13C-GBT is a practical and non-invasive method to screen for IR in adolescents with reasonable sensitivity and specificity.

Insulin sensitivity index (ISI0, 120) potentially linked to carbon isotopes of breath CO2 for pre-diabetes and type 2 diabetes

New strategies for an accurate and early detection of insulin resistance are important to delay or prevent the acute onset of type 2 diabetes (T2D). Currently, insulin sensitivity index (ISI_0,120) is considered to be a viable invasive method of whole-body insulin resistance for use in clinical settings in comparison with other invasive sensitivity indexes like homeostasis model assessment (HOMA), and quantitative insulin sensitivity check index (QUICKI). To investigate how these sensitivity indexes link the ¹³C/¹²C-carbon isotopes of exhaled breath CO₂ to pre-diabetes (PD) and type 2 diabetes in response to glucose ingestion, we studied excretion dynamics of ¹³C/¹²C-isotopic fractionations of breath CO₂. Here, we show that ¹³C/¹²C-isotope ratios of breath CO₂ were well correlated with blood glucose, insulin, glycosylated-hemoglobin as well as with HOMA-IR and 1/QUICKI. Conversely, the strongest correlation was observed between 1/ISI_0,120 and breath CO₂ isotopes. Consequently, we determined several optimal diagnostic cut-off points of 1/ISI_0,120 and ¹³CO₂/¹²CO₂-isotope ratios to distinctively track the evolution of PD prior to the onset of T2D. Our findings suggest that isotopic breath CO₂ is a novel method for accurate estimation of ISI_0,120 and thus may open new perspectives into the isotope-specific non-invasive evaluation of insulin resistance for large-scale real-time diabetes screening purposes.

The [(13)c]glucose breath test is a reliable method to identify insulin resistance in Mexican adults without diabetes: comparison with other insulin resistance surrogates

BACKGROUND

Insulin resistance (IR) precedes type 2 diabetes, but tests used to detect it in clinical settings reported poor reproducibility. We assessed the reliability of the [(13)C]glucose breath test ((13)C-GBT) in a sample of subjects without diabetes. Repeatability of the test was compared with that of other IR surrogates derived from the fasting or oral glucose tolerance test (OGTT).

SUBJECTS AND METHODS

Eighty-six healthy volunteers received an oral load of 75 g of glucose in 150 mL of water followed by 1.5 mg/kg of [U-(13)C]glucose in 50 mL of water. Breath and blood samples were collected at baseline and at 10, 20, 30, 60, 90, 120, 150, and 180 min following the glucose load; the same procedure was repeated within 1 week. The enrichment of breath (13)CO2 was measured by ratio mass spectrometry and expressed as percentage oxidized dose at a given time period. Intrasubject variability was assessed with Bland-Altman plots and coefficients of variation (CVs).

RESULTS

The overall CV of the (13)C-GBT was 12.99±11.61%, compared with 18.42% of fasting insulin, 19.44% for homeostasis model assessment, 17.06% of the composite insulin sensitivity index, and 29.99% for insulin in the 2-h oral glucose tolerance test. The variability of the (13)C-GBT tended to be higher in lean (17.40%) than in overweight (10.17%) and obese (12.61%) individuals.

CONCLUSIONS

The variability of the (13)C-GBT is lower than that of other IR surrogates, making it a reproducible method to estimate insulin sensitivity in overweight and obese adults without diabetes. Because the individuals did not have diabetes but were within a high range of insulin sensitivity, the test should have application in clinical and population-based studies, given the evidence for the utility and limitations of this surrogate.

[13C]glucose breath testing provides a noninvasive measure of insulin resistance: calibration analyses against clamp studies

BACKGROUND

Exhaled (13)CO2 following ingestion of [(13)C]glucose with a standard oral glucose tolerance load correlates with blood glucose values but is determined by tissue glucose uptake. Therefore exhaled (13)CO2 may also be a surrogate measure of the whole-body glucose disposal rate (GDR) measured by the gold standard hyperinsulinemic euglycemic clamp.

SUBJECTS AND METHODS

Subjects from across the glycemia range were studied on 2 consecutive days under fasting conditions. On Day 1, a 75-g oral glucose load spiked with [(13)C]glucose was administered. On Day 2, a hyperinsulinemic euglycemic clamp was performed. Correlations between breath parameters and clamp-derived GDR were evaluated, and calibration analyses were performed to evaluate the precision of breath parameter predictions of clamp measures.

RESULTS

Correlations of breath parameters with GDR and GDR per kilogram of fat-free mass (GDRffm) ranged from 0.54 to 0.61 and 0.54 to 0.66, respectively (all P<0.001). In calibration analyses the root mean square error for breath parameters predicting GDR and GDRffm ranged from 2.32 to 2.46 and from 3.23 to 3.51, respectively. Cross-validation prediction error (CVPE) estimates were 2.35-2.51 (GDR) and 3.29-3.57 (GDRffm). Prediction precision of breath enrichment at 180 min predicting GDR (CVPE=2.35) was superior to that for inverse insulin (2.68) and the Matsuda Index (2.51) but inferior to that for the log of homeostasis model assessment (2.21) and Quantitative Insulin Sensitivity Check Index (2.29) (all P<10(-5)). Similar patterns were seen for predictions of GDRffm.

CONCLUSIONS

(13)CO2 appearance in exhaled breath following a standard oral glucose load with added [(13)C]glucose provides a valid surrogate index of clamp-derived measures of whole-body insulin resistance, with good accuracy and precision. This noninvasive breath test-based approach can provide a useful measure of whole-body insulin resistance in physiologic and epidemiologic studies.