Dysglycemia in diabetes mellitus consists of three main components: sustained chronic hyperglycemia, GV, and hypoglycemic episodes, with each component appearing to be a link in a chain for the development and progression of diabetes-related complications [17]. Previous studies have shown that besides HbA1c, short-term daily GV represents an independent risk factor for diabetes complications [18, 19]. Furthermore, haemodialysis is another independent risk factor for GV [20]. Hence, it is paramount important to evaluate the GV among ESKD patients as they are more vulnerable to cardiovascular complications.
GV denotes swings in blood glucose level that occur throughout the day, including hypoglycemic periods, post-prandial increases, and other blood glucose fluctuations that occur at the same time on a different day [21]. In our previous study, we noted that DM-ESKD patients experienced greater fluctuations in blood glucose and had a fourfold increase in post-prandial blood glucose compared to NDM-ESKD [12]. We also noted episodes of intra-dialytic asymptomatic hypoglycemia in 12% of both DM-ESKD and NDM-ESKD patients, which demonstrated that blood glucose fluctuation occurs in all haemodialysis patients regardless of the presence of diabetes [12]. In our current study, GV among ESKD patients on haemodialysis was generally acceptable, where up to 80% and 90% of patients achieved the target GV on HDD and NHDD, respectively. We observed marked GV differences between our DM-ESKD patients with up to 33% experiencing high GV compared to NDM-ESKD (up to 12%) on HDD, which persists to NHDD (Figures 1 & 2). Interestingly, despite the absence of T2DM, a small percentage of NDM-ESKD experienced high GV on HDD with none of them showing high GV on NHDD. This observation supports the notion that haemodialysis is an independent risk factor for GV even among NDM-ESKD patients. Our findings correlate with other studies, which also show worsened glycaemic control among haemodialysis opatients and larger GV among diabetic compared to non-diabetic patients (Table 10) [13, 20, 22–25].
Although we observed a higher GV among DM-ESKD with HbA1c 8-10%, the sole use of HbA1c in ESKD is limited by several factors, e.g., anaemia, uremia, acidosis, and malnutrition [26]. In the general population, there is a linear relationship between HbA1c and mean blood glucose with R2 more than 0.80, which makes HbA1c as an excellent surrogate marker for glycaemic control [27]. In our study, the relationships between mean blood glucose and HbA1c were moderate, with R2 = 0.59 [12]. Our result was similar to bigger studies among haemodialysis patients, where the relationship (R2) is not more than 0.50 [28]. Therefore, knowledge of factors associated with GV apart from HbA1c as a surrogate marker is essential as it allows health professionals to provide targeted interventions to patients with a higher risk of diabetic complications. Currently, many studies that investigate factors affecting GV were done amongst diabetic patients with normal renal function. Moreover, results from these studies varied among each other with small sample size and different indexes of measuring GV [29–38].
We found that GV is higher in patients with older age, DM-ESKD, and hyperlipidemia. Blood parameters associated with high GV were HbA1c, ferritin level, lipid profile, and albumin. HbA1c and its association with GV and mean blood glucose among patients had been heavily investigated with inconsistent results. In our study, HbA1c, especially levels between 8 and 10%, was associated with higher GV. Current literature on the association of HbA1c with GV is heterogeneous, with results showing a weak correlation between HbA1c and GV but had a significant association with chronic hyperglycemia and average blood glucose [29, 30, 32, 33] Conversely, recent studies among Asian populations, showed similar findings with our study where HbA1c correlates well with GV indices [34, 35]. However, most of these studies include only patients with normal renal function in whom HbA1c is more reliable as a surrogate marker and would not be affected by the anaemia commonly seen in ESKD patients.
GV may be related to pancreatic beta-cell dysfunction and insulin resistance, which may occur part of the aging process and duration of T2DM. In our study, older age was associated with higher GV, which corroborates a previous Asian study that showed an association of GV with older age, longer duration of diabetes, and low c-peptide [34, 35]. Types of medication also may reflect the process of pancreatic beta-cell dysfunction. Although no association between GV with types of medication was found in this study, previous studies showed an association between the use of insulin and sulfonylureas (insulin secretagogues) with higher GV [31, 37, 38]. In T2DM, beta-cell dysfunction plays a significant role in dysglycaemia, where insufficient insulin secretion for accurate regulation may lead to glucose-related metabolic disorders, exposing patients to increased GV and sustained hyperglycemia [39–41]. Furthermore, aging alone significantly affects pancreatic B cells due to deterioration in secretory and regenerative capacity [42, 43].
Hyperlipidaemia is recognised as a risk factor for IHD and coronary mortality and was associated with high GV in our study [44, 45]. High-sensitive C-reactive protein (hs-CRP) was used to estimate cardiovascular risk in our population, and although it did not have a significant association with GV, we found that both DM-ESKD and NDM-ESKD patients had higher hs-CRP levels with a mean of 8.91 mg/L and 7.03 mg/L respectively [12]. GV may further increase cardiovascular risk by propagating oxidative stress, leading to endothelial dysfunction and angiopathies [46]. In our study, higher ferritin, although a non-specific inflammatory marker, was seen more frequently in the target GV group compared to the high GV group. Nonetheless, patients with high GV also demonstrate high ferritin level with a mean value 554.1 ug/L. Although a significant number of our patients were on iron supplementation, we found the level of ferritin is independent of hs-CRP, a better marker for inflammation in cardiovascular disease. High ferritin and quantitative C-reactive protein levels have been associated with accelerated atherosclerosis in ESKD patients; however, it is unclear to us whether ferritin levels can be reliably interpreted in patients on iron supplementation [47]. A study using a more specific marker for oxidative stress, N, N-diethyl paraphenylenediamine, showed an association between high GV and high oxidative stress [48]. In our cohort, the albumin level was lower among DM-ESKD as compared to NDM-ESKD and was associated with high GV. LDL, although not a significant factor for GV was also lower in DM-ESKD, which may represent nutritional status among diabetic patients. Notably, it had a poor correlation with albumin in our study. A 10-year cohort study evaluated serum albumin, C-reactive protein, and carotid atherosclerosis as predictors of 10-year mortality in haemodialysis patients showed that serum albumin concentration was a better predictor of mortality [50]. Hence, targeting chronic inflammation and improving nutrition, and observing the effect on GV could be a subject for future research.
The limitations of our study are the cross-sectional design, utilisation of SMBG instead of continuous glucose monitoring, which is more accurate in assessing GV, and possibly the lack of standardised dietary restriction in our patients. We elected for SMBG due to ease of availability and lower cost, which makes it the preferred method for glucose monitoring in our population. We did not limit or measure the dietary intake of the patients during the study period, which may make it a confounding factor in the glycaemic profile of the patients. Some previous studies restricted dietary intake or mandated fasting during HD, however, the readings would not be representative of normal day-to-day glucose fluctuations. Therefore by allowing usual dietary intake, it would be more practical, reflective of real-life data, and may subsequently allow alterations in management.