Hypoglycaemia in cystic fibrosis in the absence of diabetes: A systematic review

Hypoglycemia in children and young adults with cystic fibrosis during oral glucose tolerance testing vs. continuous glucose monitoring

BACKGROUND

Hypoglycemia is common in people with cystic fibrosis (pwCF) during oral glucose tolerance tests (OGTTs) and in the free-living setting, yet its pathophysiology remains unclear.

OBJECTIVE

To evaluate hypoglycemia in children and young adults with CF by OGTT and continuous glucose monitoring (CGM).

METHODS

A 3-h OGTT was performed in children and young adults with CF and healthy controls (HC). Individuals were classified as experiencing hypoglycemia on OGTT (glucose <70 mg/dL) or not. Insulin, C-peptide, glucose, glucagon, and incretins were measured. CGM was performed for 7 days in the free-living setting. Measures of insulin sensitivity, beta cell function accounting for insulin sensitivity, and insulin clearance were calculated.

RESULTS

A total of 57 participants (40 CF and 17 HC) underwent assessment. Rates of hypoglycemia by OGTT were similar in pwCF (53%, 21/40) compared to HC (35%, 6/17), p = 0.23. PwCF compared to HC had higher A1c; on OGTT higher and later glucose peaks, later insulin peaks; and on CGM more glucose variability. CF Hypo+ versus CF Hypo- had higher lung function, higher insulin sensitivity, higher beta cell function accounting for insulin sensitivity, and decreased CGM variability. When comparing CF Hypo+ to HC Hypo+, although rates of hypoglycemia are similar, pwCF had blunted glucagon responses to hypoglycemia. OGTT hypoglycemia was not associated with CGM hypoglycemia in any group.

CONCLUSION

Youth with CF have increased insulin sensitivity and impaired glucagon response to hypoglycemia on OGTT. Hypoglycemia on OGTT did not associate with free-living hypoglycemia.

Screening strategies for glucose tolerance abnormalities and diabetes in people with cystic fibrosis

The increase in life expectancy of patients with cystic fibrosis has come with new comorbidities, particularly diabetes. The gradual development of glucose tolerance abnormalities means that 30 to 40% of adults will be diabetic. Cystic fibrosis-related diabetes is a major challenge in the care of these patients because it is a morbidity and mortality factor at all stages of the disease. Early glucose tolerance abnormalities observed from childhood, before the stage of diabetes, are also associated with a poor pulmonary and nutritional outcome. The long asymptomatic period justifies systematic screening with an annual oral glucose tolerance test from the age of 10 years. However, this strategy does not take into account the new clinical profiles of patients with cystic fibrosis, recent pathophysiological knowledge of glucose tolerance abnormalities, and the emergence of new diagnostic tools in diabetology. In this paper, we summarise the challenges of screening in the current context of new patient profiles - patients who are pregnant, have transplants, or are being treated with fibrosis conductance transmembrane regulator modulators - and put forward an inventory of the various screening methods for cystic fibrosis-related diabetes, including their applications, limitations and practical implications.

Vitamin C deficiency induces hypoglycemia and cognitive disorder through S-nitrosylation-mediated activation of glycogen synthase kinase 3β

Vitamin C (VC, l-ascorbic acid) is an essential nutrient that plays a key role in metabolism and functions as a potent antioxidant in regulating the S-nitrosylation and denitrosylation of target proteins. The precise function of VC deprivation in glucose homeostasis is still unknown. In the absence of L-gulono-1,4-lactone oxidoreductase, an essential enzyme for the last step of VC synthesis, VC deprivation resulted in persistent hypoglycemia and subsequent impairment of cognitive functions in female but not male mouse pups. The cognitive disorders caused by VC deprivation were largely reversed when these female pups were given glucose. VC deprivation-induced S-nitrosylation of glycogen synthase kinase 3β (GSK3β) at Cys14, which activated GSK3β and inactivated glycogen synthase to decrease glycogen synthesis and storage under the feeding condition, while VC deprivation inactivated glycogen phosphorylase to decrease glycogenolysis under the fasting condition, ultimately leading to hypoglycemia and cognitive disorders. Treatment with Nω-Nitro-l-arginine methyl ester (l-NAME), a specific inhibitor of nitric oxide synthase, on the other hand, effectively prevented S-nitrosylation and activation of GSK3β in female pups in response to the VC deprivation and reversed hypoglycemia and cognitive disorders. Overall, this research identifies S-nitrosylation of GSK3β and subsequent GSK3β activation as a previously unknown mechanism controlling glucose homeostasis in female pups in response to VC deprivation, implying that VC supplementation in the prevention of hypoglycemia and cognitive disorders should be considered in the certain groups of people, particularly young females.

Can continuous glucose monitoring predict cystic fibrosis-related diabetes and worse clinical outcome?

Objective:

To determine whether abnormal continuous glucose monitoring (CGM) readings (hypoglycemia/hyperglycemia) can predict the onset of cystic fibrosis-related diabetes (CFRD) and/or clinical impairment (decline in BMI and/or FEV₁) in pediatric patients with cystic fibrosis (CF).

Methods:

This was a longitudinal prospective cohort study involving CF patients without diabetes at baseline. The mean follow-up period was 3.1 years. The patients underwent 3-day CGM, performed oral glucose tolerance test (OGTT), and had FEV₁ and BMI determined at baseline. OGTT, FEV_1, and BMI were reassessed at the end of the follow-up period.

Results:

Thirty-nine CF patients (10-19 years of age) had valid CGM readings at baseline, and 34 completed the follow-up period (mean = 3.1 ± 0.5 years). None of the study variables predicted progression to CFRD or were associated with hypoglycemic events. CGM could detect glucose abnormalities not revealed by OGTT. Patients with glucose levels ≥ 140 mg/dL, as compared with those with lower levels, on CGM showed lower BMI values and z-scores at baseline-17.30 ± 3.91 kg/m² vs. 19.42 ± 2.07 kg/m²; p = 0.043; and −1.55 ± 1.68 vs. −0.17 ± 0.88; p = 0.02, respectively-and at the end of follow-up-17.88 ± 3.63 kg/m² vs. 19.95 ± 2.56 kg/m²; p = 0.039; and −1.65 ± 1.55 vs. −0.42 ± 1.08; p = 0.039. When comparing patients with and without CFRD, the former were found to have worse FEV₁ (in % of predicted)-22.67 ± 5.03 vs. 59.58 ± 28.92; p = 0.041-and a greater decline in FEV₁ (−36.00 ± 23.52 vs. −8.13 ± 17.18; p = 0.041) at the end of follow-up.

Conclusions:

CGM was able to identify glucose abnormalities not detected by OGTT that were related to early-stage decreases in BMI. CGM was ineffective in predicting the onset of diabetes in this CF population. Different diagnostic criteria for diabetes may be required for individuals with CF.

Spontaneous and iatrogenic hypoglycemia in cystic fibrosis

Spontaneous episodes of hypoglycemia can occur in people with cystic fibrosis (CF) without diabetes, who are not on glucose lowering medications. Spontaneous hypoglycemia in CF could occur both in the fasting or postprandial state (reactive hypoglycemia). The pathophysiology of fasting hypoglycemia is thought to be related to malnutrition and increased energy expenditure in the setting of inflammation and acute infections. Reactive hypoglycemia is thought to be due to impaired first phase insulin release in response to a glucose load, followed by a delayed and extended second phase insulin secretion; ineffective counterregulatory response to dropping glucose levels may also play a role. The overall prevalence of spontaneous hypoglycemia varies from 7 to 69% as examined with oral glucose tolerance test (OGTT) or with continuous glucose monitoring (CGM) under free living conditions. Spontaneous hypoglycemia in CF is associated with worse lung function, higher hospitalization rates, and worse clinical status. In addition, patients with CF related diabetes on glucose-lowering therapies are at risk for iatrogenic hypoglycemia. In this article, we will review the pathophysiology, prevalence, risk factors, clinical implications, and management of spontaneous and iatrogenic hypoglycemia in patients with CF.

Hypoglycemia in cystic fibrosis: Prevalence, impact and treatment

Hypoglycemia is a common and feared complication of insulin therapy. As in type 1 and type 2 diabetes, people with cystic fibrosis related diabetes are also at risk for hypoglycemia related to insulin therapy. Spontaneous hypoglycemia is also common in patients with CF without diabetes, who are not on glucose lowering medications. Spontaneous hypoglycemia in CF may also occur during or after an oral glucose tolerance test. In this review, we will discuss the definition, epidemiology, pathophysiology and impact of hypoglycemia, with a focus on people with cystic fibrosis. We will also review strategies to manage and prevent hypoglycemia.

Hypoglycemia in cystic fibrosis during an extended oral glucose tolerance test

BACKGROUND

Hypoglycemia in cystic fibrosis (CF), in the absence of glucose-lowering therapies, has long been identified as an important issue in the management of CF. There is currently still no unifying hypothesis for its etiology.

AIM

The aims of this study were to perform a 3-h oral glucose tolerance test (OGTT) in participants with CF and (1) document glucose, insulin, glucagon, glucagon-like-peptide-1 (GLP-1), and glucose-dependent insulinotropic peptide (GIP) release patterns within varying glucose tolerance groups during the OGTT; (2) determine the prevalence of hypoglycemic during the OGTT; and (3) define any association between hypoglycemia and patterns of insulin, glucagon, GLP-1, and GIP release.

METHODS

Eligible participants attending an adult CF clinic completed a 3-h OGTT. Hypoglycemia on OGTT was defined as mild (glucose 3.4-3.9 mmol/L), moderate (glucose 3.1-3.3 mmol/L), and severe (glucose ≤ 3 mmol/L). Hormones were measured at fasting, 30, 60, 120, and 180 min.

RESULTS

Twenty-four participants completed the study, of which 7 had normal glucose tolerance, 12 had abnormal glucose tolerance, and 5 had cystic fibrosis related diabetes (CFRD). All participants had a delayed insulin response compared with normative data. All glucose tolerance groups showed appropriate and similar suppression of fasting glucagon. Four participants (17%) had mild hypoglycemic, three (13%) had moderate hypoglycemic, and eight (33%) had severe hypoglycemic. No participant with CFRD demonstrated hypoglycemic. Of the 19 participants without CFRD, 15 (79%) experienced hypoglycemic. Participants with hypoglycemic had greater peak glucose and insulin responses than those that did not have hypoglycemic, and this approached significance (p = .0625 for glucose and p = .0862 for insulin). No significant mean differences between GLP-1 and GIP release were found. There was no relationship between hypoglycemic and modulator therapy.

CONCLUSION

Postprandial hypoglycemic was unmasked by the extension of an OGTT to 3 h. Delayed and abnormal insulin release, and ineffective counter-regulatory action of glucagon may have a role in its etiology.

Overview of Atypical Diabetes

Although type 1 diabetes mellitus and, to a lesser extent, type 2 diabetes mellitus, are the prevailing forms of diabetes in youth, atypical forms of diabetes are not uncommon and may require etiology-specific therapies. By some estimates, up to 6.5% of children with diabetes have monogenic forms. Mitochondrial diabetes and cystic fibrosis related diabetes are less common but often noted in the underlying disease. Atypical diabetes should be considered in patients with a known disorder associated with diabetes, aged less than 25 years with nonautoimmune diabetes and without typical characteristics of type 2 diabetes mellitus, and/or with comorbidities associated with atypical diabetes.

Hypoglycemia and Islet Dysfunction Following Oral Glucose Tolerance Testing in Pancreatic-Insufficient Cystic Fibrosis

CONTEXT

Oral glucose tolerance test (OGTT)-related hypoglycemia is common in pancreatic-insufficient cystic fibrosis (PI-CF), but its mechanistic underpinnings are yet to be established.

OBJECTIVE

To delineate the mechanism(s) underlying OGTT-related hypoglycemia.

DESIGN AND SETTING

We performed 180-minute OGTTs with frequent blood sampling in adolescents and young adults with PI-CF and compared results with those from a historical healthy control group. Hypoglycemia (Hypo[+]) was defined as plasma glucose <65 mg/dL. We hypothesized that CF-Hypo[+] would demonstrate impaired early phase insulin secretion and persistent late insulin effect compared with control-Hypo[+], and explored the contextual counterregulatory response.

MAIN OUTCOME MEASURE

OGTT 1-hour and nadir glucose, insulin, C-peptide, and insulin secretory rate (ISR) incremental areas under the curve (AUC) between 0 and 30 minutes (early) and between 120 and 180 minutes (late), and Δglucagon120-180min and Δfree fatty acids (FFAs)120-180min were compared between individuals with CF and control participants with Hypo[+].

RESULTS

Hypoglycemia occurred in 15/23 (65%) patients with CF (43% female, aged 24.8 [14.6-30.6] years) and 8/15 (55%) control participants (33% female, aged 26 [21-38] years). The CF-Hypo[+] group versus the control-Hypo[+] group had higher 1-hour glucose (197 ± 49 vs 139 ± 53 mg/dL; P = 0.05) and lower nadir glucose levels (48 ± 7 vs 59 ± 4 mg/dL; P < 0.01), while insulin, C-peptide, and ISR-AUC0-30 min results were lower and insulin and C-peptide, and AUC120-180min results were higher (P < 0.05). Individuals with CF-Hypo[+] had lower Δglucagon120-180min and ΔFFA120-180min compared with the control-Hypo[+] group (P < 0.01).

CONCLUSIONS

OGTT-related hypoglycemia in PI-CF is associated with elevated 1-hour glucose, impaired early phase insulin secretion, higher late insulin exposure, and less increase in glucagon and FFAs. These data suggest that hypoglycemia in CF is a manifestation of islet dysfunction including an impaired counterregulatory response.

Hypoglycemic risk exposures in relation to low serum glucose values in ambulatory patients

This study aimed to correlate hypoglycemic risk exposures (HREs) with low blood glucose value (BGV) in ambulatory patients to inform selection of a glucose critical action value (CAV).This was a retrospective study of ambulatory patients with at least 1 serum glucose ≤70 mg/dL obtained at 2 laboratories within the Johns Hopkins Health System over 3.8 years. Multivariable logistic regression was used to evaluate association of BGV cut-offs of <60, <54, <50, and <45 mg/dL with HREs. HREs were classified as "high hypoglycemic risk" (HHR), "moderate hypoglycemic risk" (MHR), "low hypoglycemic risk" (LHR), and "no hypoglycemic risk" (NHR).A total of 5404 patient samples of BG ≤70 mg/dL were analyzed, of which 30.3%, 23.2%, 28.5%, 18.0% occurred in NHR, LHR, MHR, and HHR groups, respectively. An inverse relationship was noted between BGV cut-offs and HHR, but no association was observed for LHR or MHR. After adjusting for age, sex, and race, there was an inverse association between BG thresholds and the odds of HHR. For classification of HHR, BGV cut-offs of <60, <54, <50, and <45 mg/dL correctly classified 71.2%, 69.8%, 68.8%, and 67.2% of BG samples, achieved false-positive rates of 13.6%, 4.7%, 1.7%, and 0.5% and positive likelihood ratios of 3.3, 6.0, 11.2, and 23.4, respectively.Nearly 70% of low BGVs occurred in patients with at least 1 HRE, but only ∼20% occurred in HHR patients. Given their high positive likelihood ratios, BGVs <54 or <50 mg/dL are reasonable candidates for CAVs that would allow sufficient clinician response time while minimizing false-positive alerts.

Dysregulated insulin in pancreatic insufficient cystic fibrosis with post-prandial hypoglycemia

BACKGROUND

Post-prandial and oral glucose tolerance test-related hypoglycemia is common in cystic fibrosis (CF); however, the underlying mechanisms are unclear.

METHODS

To understand the relationship of hypoglycemia with meal-related glucose excursion and insulin secretion, we analyzed plasma glucose, insulin, C-peptide, glucagon and incretins obtained during standardized mixed-meal tolerance tests (MMTT) in non-diabetic adolescents and young adults with pancreatic insufficient CF (PI-CF).

RESULTS

Hypoglycemia, defined as glucose <70 mg/dL, occurred in 9/34 subjects at 150 (range:120-210) minutes following initial meal ingestion. Hypoglycemia[+] and hypoglycemia[-] groups did not differ in gender, age, lung function, HbA1c, or BMI. While 11/14 hypoglycemia[-] individuals displayed normal glucose tolerance (NGT), only 2/9 hypoglycemia[+] had NGT. Peak glucose was higher in hypoglycemia[+] vs hypoglycemia[-]. Compared to hypoglycemia[-] NGT, hypoglycemia[+] exhibited lower early-phase insulin secretion (ISR-AUC_0-30min). ISR-AUC_120-180min was not different in hypoglycemia[+] vs hypoglycemia[-] with abnormal glucose tolerance (AGT); however, glucose-AUC_120-180min was lower in hypoglycemia[+] vs hypoglycemia[-] AGT. After adjusting for glucose-AUC, hypoglycemia[+] subjects tended to have higher ISR-AUC_120-180min than hypoglycemia[-] AGT. Glucagon concentration did not differ between groups. Lower GLP-1-AUC_30min and AUC_180min and higher GIP-AUC_30min were present in hypoglycemia[+] individuals.

CONCLUSION

Hypoglycemia is common in PI-CF following MMTT and is associated with early glucose dysregulation (higher peak glucose), more impaired early-phase insulin secretion (lower ISR-AUC_30min), and possibly late compensatory hyperinsulinemia. Further study is required to understand whether absence of glucagon difference in the hypoglycemia[+] individuals signals counterregulatory impairment, to delineate the role of incretins in hypoglycemia, and to determine the relationship of hypoglycemia to emergence of CFRD.

Continuous glucose monitoring abnormalities in cystic fibrosis youth correlate with pulmonary function decline

BACKGROUND

To characterize glucose patterns with continuous glucose monitoring (CGM) in cystic fibrosis (CF) and assess relationships between CGM and clinical outcomes.

METHODS

110 CF youth and healthy controls (HC), 10-18 years, wore CGM up to 7 days. Correlations between CGM and lung function and BMI z-score change over the prior year were determined.

RESULTS

Multiple CGM measures were higher in CF Normal Glycemic (CFNG) youth versus HC (peak glucose, excursions >140 mg/dl/day, %time > 140 mg/dl, standard deviation (SD) and mean amplitude of glycemic excursions (MAGE)). Hypoglycemia was no different among groups. In CF, decline in FEV1% and FVC% correlated with maximum CGM glucose, excursions >200 mg/dl/day, SD, and MAGE.

CONCLUSIONS

CFNG youth have higher glucoses and glucose variability than HC on CGM. Higher and more variable glucoses correlate with lung function decline. Whether earlier treatment of CGM abnormalities improves lung function in CF requires further study.

Prevalence of hypoglycemia during oral glucose tolerance testing in adults with cystic fibrosis and risk of developing cystic fibrosis-related diabetes

BACKGROUND

Hypoglycemia in cystic fibrosis (CF) patients during the oral glucose tolerance test (OGTT) has been reported; however, these patients have not been well-characterized. Few studies have examined whether hypoglycemia during the OGTT increases the risk of developing CF-related diabetes (CFRD). Objectives of this study were to describe the characteristics of CF patients with hypoglycemia during the OGTT and to determine the incidence and time to development of CFRD in those with hypoglycemia.

METHODS

This cohort study included 466 adults with CF at the Toronto Adult CF Clinic between 1996 and 2015. Subjects were classified into two groups based on their plasma glucose (PG) level 2 h after a 75 g OGTT: hypoglycemia (PG ≤ 3.9 mmol/L) or no hypoglycemia (PG > 3.9 mmol/L). Clinical and demographic data were collected from the clinic visit closest to the OGTT. Differences between groups were assessed using Fisher's exact test or Mann-Whitney-Wilcoxon test.

RESULTS

138 patients (29.6%) experienced hypoglycemia during the OGTT. More males experienced hypoglycemia compared to no hypoglycemia (69.6% vs. 54.6% respectively; p = 0.003). Those who were heterozygous deltaF508 were more likely to experience hypoglycemia (p = 0.006). Subjects who experienced hypoglycemia were less likely to develop CFRD at ten years compared to no hypoglycemia (12.0% vs. 42.1%, respectively; p < 0.001).

CONCLUSIONS

Hypoglycemia following OGTT is common in CF however the 10 year risk of developing CFRD in these patients was low. Males and those who were heterozygous deltaF508 were at higher risk for hypoglycemia.

Hypoglycaemia in cystic fibrosis: An analysis of a single centre adult cystic fibrosis clinic

BACKGROUND

Hypoglycaemia in cystic fibrosis (CF) is known to occur during oral glucose tolerance tests (OGTT) and continuous glucose monitoring, however demographic, clinical and mechanistic data are limited. The aims of this study were to review patient electronic medical records (EMR) in order to 1) describe patient characteristics of a university teaching hospital CF clinic, 2) determine the prevalence of hypoglycaemia on OGTT and explore associations with demographic and clinical characteristics, and 3) explore patient reported symptoms suggestive of hypoglycaemia documented in the EMR.

METHODS

Adults who attended the RPA CF clinic between January 2009 to April 2016 were included in the study. The prevalence of hypoglycaemia on OGTT was determined and clinical and demographic data were compared to age, sex and glucose tolerance matched controls. Reported symptoms suggestive of hypoglycaemia documented in EMR were qualitatively explored.

RESULTS

Hypoglycaemia on OGTT was prevalent in 25 (3 fasting and 22 reactive) of 169 patients who had an OGTT. They were heavier, less likely to have pancreatic insufficiency and had a lower insulin response at 2-h. Another 14 patients reported symptoms suggestive of hypoglycaemia in their EMR. No patient appropriately suppressed insulin at 2-h on OGTT.

CONCLUSIONS

This study identified two potentially different presentations of hypoglycaemia occur in different clinic sub-populations. Knowledge gaps in the aetiology and triggers of hypoglycaemia remain.