Serum 1,5-Anhydroglucitol to Glycated Albumin Ratio Can Help Early Distinguish Fulminant Type 1 Diabetes Mellitus from Newly Onset Type 1A Diabetes Mellitus

Background Fulminant type 1 diabetes mellitus (FT1DM) onsets abruptly and usually occurs within 1 week after the onset of hyperglycemic symptoms. Glycated albumin (GA) and 1,5-anhydroglucitol (1,5-AG) are indicators that reflect short-term glucose levels. This study was aimed at investigating whether the 1,5-AG/GA index (AGI) is a suitable indicator for early FT1DM identification. Methods A total of 226 subjects were enrolled, all with glycated hemoglobin A1c (HbA1c) < 8.7%. FT1DM was diagnosed based on the 2012 Japan Diabetes Society criteria. Results The AGI level was 0.54 (0.17–1.36) in the whole group. It was lower in FT1DM patients (0.16 [0.10–0.25]). Among the participants whose HbA1c did not exceed 7.0%, the AGI of FT1DM decreased significantly compared to type 1A diabetes (T1ADM) and latent autoimmune diabetes in adults (LADA) patients (0.16 [0.12–0.26] vs. 0.46 [0.24–0.72] vs. 0.46 [0.24–0.72] P < 0.05). The receiver operating characteristic (ROC) curve showed that AGI can be used to distinguish FT1DM and T1ADM patients with HbA1c < 8.7%. Diagnosing FT1DM based on AGI ≤ 0.3 only can help narrow down suspected FT1DM by up to 26.87%. If we diagnosed FT1DM when AGI was ≤0.3 and HbA1c was ≤7.0%, the success rate further increased to 86.57%, among which 85.00% of FT1DM and 87.23% of T1ADM patients were successfully identified. Therefore, using the combination criteria of AGI and HbA1c would improve the differential diagnosis efficacy by 61.11% compared with the AGI criterion only. Conclusion AGI can help facilitate the early differential diagnosis of FT1DM and T1ADM when HbA1c < 8.7%, with an optimal cut-off point of 0.3.


Introduction
Fulminant type 1 diabetes mellitus (FT1DM) is a new subtype of type 1 diabetes mellitus that is mainly characterized by an abrupt onset of a severe metabolic disorder, markedly elevated blood glucose level, normal or slightly elevated glycated hemoglobin A 1c (HbA 1c ), and almost complete or complete irreversible islet dysfunction [1,2]. At present, FT1DM is mainly diagnosed based on the 2012 Japan Diabetes Society (JDS) criteria [3], specifically, based on the duration of symptoms, HbA 1c , and C-peptide (both fasting and postload). However, HbA 1c has certain limitations since it mainly reflects the average blood glucose level of the past 2 to 3 months, which far exceeds the duration of FT1DM [4].
Moreover, the diagnosis of FT1DM is sometimes difficult to confirm, for two reasons: (1) because of its onset with diabetic ketosis (DK) or diabetic ketoacidosis (DKA), the patients are mostly in a fasting state, and the postload Cpeptide cannot be obtained in a timely manner; (2) some type 1A diabetes (T1ADM) (i.e., classic type 1 diabetes) onsets with a HbA 1c less than 8.7%. Therefore, it is important to effectively identify FT1DM early, especially in patients with HbA 1c < 8:7%.
1,5-Anhydroglucitol (1,5-AG) has recently attracted extensive attention worldwide because it represents the average glucose of the past 1 to 2 weeks in diabetic patients and has some advantages in reflecting glucose fluctuations and postprandial hyperglycemia when compared with HbA 1c [5][6][7]. Several studies have shown that 1,5-AG is stable in vivo and decreases with increasing glucose level. Glycated albumin (GA), an indicator that reflects 2-to 3-week average glucose level, is recommended in stress hyperglycemia and has therapeutic effects evaluating after hypoglycated agent adjustment [8][9][10].
Therefore, we speculate that the 1,5-AG/GA index (AGI), combined with 1,5-AG and GA, can better compensate for the deficiency of HbA 1c in reflecting short-term glucose levels and help facilitate the differential diagnosis of FT1DM and T1ADM in patients whose HbA 1c < 8:7%. That is, the lower the AGI, the more likely FT1DM is. Therefore, the goal of the current study is to explore the AGI levels of subjects with different glucose metabolism statuses in the Chinese population and to clarify the identification efficacy and the optimal cut-off point of AGI for distinguishing FT1DM and T1ADM patients with HbA 1c < 8:7%.

Study Population.
Twenty subjects who were first hospitalized and diagnosed with FT1DM (with their duration of symptoms ≤ 2 weeks and had complete clinical data and blood sample) in the Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, from January 2007 to July 2018 were recruited. Sex-and age-matched patients with newly diagnosed T1ADM (n = 47), type 2 diabetes mellitus patients (T2DM, n = 42) and nondiabetic participants (non-DM, n = 81; specifically, 33 with normal glucose tolerance and 48 with impaired glucose tolerance) through Propensity Score matching were included. In addition, 36 latent autoimmune diabetes in adults (LADA) patients with complete data were included. All subjects had an HbA 1c less than 8.7%. Finally, a total of 226 subjects were enrolled in this study.
This study was approved by the Ethics Committee of Shanghai Jiao Tong University Affiliated Sixth People's Hospital and followed the 1964 Declaration of Helsinki. Informed consent was obtained from all subjects enrolled in the current study.
The glucose metabolism status determination and diabetes classification were determined based on 2010 American Diabetes Association (ADA) standards and the report of the expert committee on the diagnosis and classification of diabetes mellitus [11,12].

Anthropometric and Biochemical
Assessments. All subjects underwent a complete physical examination, including height, body weight, and blood pressure. Related informa-tion, including medical history, past history, and family history, was obtained. The body mass index (BMI) was defined as body weight/height 2 (kg/m 2 ). Laboratory data such as plasma glucose, HbA 1c , GA, fasting C-peptide, and 2-hour C-peptide were collected. Serum 1,5-AG levels were measured by an enzymatic method (GlycoMark; GlycoMark Inc., New York, NY, USA) on a 7600 autoanalyzer (Hitachi, Tokyo, Japan) with intra-assay and interassay coefficients of variation (CVs) of <2.5% and <3.5%, respectively. GA was measured using an enzyme-based assay kit (Lucica GA-L, Asahi Kasei Pharma, Tokyo, Japan) on the 7600-120 automatic biochemistry analyzer (Hitachi, Tokyo, Japan). The intra-assay and interassay CVs were <3.5% and <5.0%, respectively. High-pressure liquid chromatography was used to quantify the levels of HbA 1c on a Variant II hemoglobin analyzer (Bio-Rad, Hercules, CA, USA). The other indexes were determined with standard methods [2].

Statistical
Analysis. Data were analyzed with SPSS version 24.0 (SPSS, Inc., Chicago, IL, USA) and MedCalc version 15.2 (MedCalc Inc., Ostend, Belgium). All continuous variables are nonnormally distributed and presented as medians with interquartile ranges. Categorical variables are presented as percentages (%). The Mann-Whitney U test and the Kruskal-Wallis test were carried out for intergroup comparisons of nonnormally distributed variables, and the chi-squared test was used for intergroup comparisons of categorical variables. Sex-and age-matched patients were matched through the propensity score matching method. The receiver operating characteristic (ROC) curve was generated to analyze the value of related indicators in FT1DM identification. The optimal cut-off point was confirmed based on the Youden index. A P value of < 0.05 (two-tailed) was considered to be statistically significant. Table 1, a total of 226 subjects were enrolled in the current study, with 146 males and 80 females aged 41 (30-51) years old. The age of LADA patients was significantly higher than that of other groups (P < 0:01). Subjects with non-DM and T2DM had a significantly higher BMI than FT1DM, T1ADM, and LADA patients (all P < 0:01).

Discussion
This is the first study to propose the new blood glucose monitoring parameter AGI. We noted that for individuals with newly diagnosed type 1 diabetes whose HbA 1c was less than 8.7%, the AGI criteria alone can help reduce the scope of the suspected FT1DM population by approximately 1/4, 3 Journal of Diabetes Research while the combined criteria of AGI and HbA 1c can successfully identify 5/6 patients, with an optimal cut-off point for AGI of 0.3.
FT1DM, a clinically critical illness, may result in serious complications, such as rhabdomyolysis, multiple organ failure, and acute renal failure [13][14][15], and may be diagnosed based on HbA 1c , fasting C-peptide, and postload C-peptide. However, the postload C-peptide is often unavailable because of their fasting status at the time of the initial visit. Thus, it is of particular importance to seek a suitable indicator that can be tested in nonfasting status to distinguish FT1DM and T1ADM as early as possible, especially among those whose HbA 1c < 8:7%.
1,5-AG, a six-carbon monosaccharide, is stable in vivo and can be used for nonfasting detection [5,16]. The reabsorption process of 1,5-AG can be competitively inhibited by glucose, which leads to a decline in serum 1,5-AG level under conditions of hyperglycemia, making 1,5-AG a shortterm (1-2 weeks) glucose monitoring indicator [17,18]. In addition, our recent study showed that the decrease in the AH index (formed by 1,5-AG combined with HbA 1c ) was an indication of recent intensified glucose metabolic  Journal of Diabetes Research disorders with poor islet β cell function [19]. GA is an indicator that mainly monitors the 2 to 3 weeks average glucose, has a good correlation with HbA 1c , and is negatively correlated with serum 1,5-AG level. Consistent with our previous study [20], the indicator reflecting long-term glucose level (i.e., HbA 1c ) has not changed significantly, though higher than nondiabetic subjects, but much lower than other types of diabetic patients. However, in conformity with the extremely high onset plasma glucose level, the short-term indicator GA increased to 21.7% and 1,5-AG decreased to 3.5 μg/mL, exceeding the cut-off value of GA (17.1%), which is used to detect diabetes in the Chinese population [21], and lower than 15.9 μg/mL, which is the cut-off point to screen diabetes [22]. All these results are in accordance with the clinical features of abrupt onset and rapid development of FT1DM.
Moreover, we propose a new glucose monitoring parameter, AGI, that combines 1,5-AG with GA and may enhance the advantages of both indicators in reflecting short-term glucose level. We found that AGI was highest in non-DM individuals, second-highest by T2DM, and lowest in patients with FT1DM, T1ADM, and LADA. The trend of AGI in participants with different glucose metabolism statuses was consistent with serum 1,5-AG and opposite to the GA trend. HbA 1c was lowest in non-DM participants, followed by FT1DM, and highest in T1ADM, LADA, and T2DM patients. The phenomenon that the trends of HbA 1c and AGI were not exactly the same further verifies the characteristics of FT1DM of sudden onset and usually <1-week duration of symptoms.
We also noted for the first time that AGI can be used to distinguish T1ADM with HbA 1c < 8:7% and FT1DM, and  the combination of AGI and HbA 1c performed the best for early identification. A study conducted by Koga et al. [23] enrolled 38 FT1DM and 31 acute-onset T1ADM patients and found that 8.7% was the optimal cut-off point of HbA 1c for identification. Additionally, whether GA exceeded 33.5% can be applied for differential diagnosis. A related study took 1,5-AG into consideration and included 7 FT1DM patients and 32 T2DM patients with HbA 1c less than 8.5% (JDS standard). The results demonstrated that 1,5-AG can be used to identify T2DM and FT1DM, but its sensitivity is slightly lower than that of GA [4]. Another study, also conducted by Koga et al. [24] in the same period, included 35 FT1DM patients and 42 T2DM participants whose HbA 1c was <8.5% (JDS standard), and the results indicated that GA/HbA 1c > 3:2 should be the best distinguishing indicator. In contrast to all three studies mentioned above, this study focused on T1ADM with HbA 1c < 8:7% and FT1DM. Our results demonstrated that by diagnosing FT1DM when AGI ≤ 0:3, 95.00% of FT1DM can be identified successfully, and the suspected FT1DM group was narrowed down by more than 1/4. Based on FT1DM and acute-onset type 1 diabetes individuals, the JDS results showed that 70.2% of participants had an onset HbA 1c < 7:0%, and the average onset HbA 1c in patients with FT1DM was 6.8%. The specificity of FT1DM diagnoses can reach 100.0% if the set cut-off point of Hb A 1c ðNGSPÞ ≤ 8:5% [3]. In the current study, the overall average of HbA 1c was similar to 6:4 ± 0:9% of the Japanese patient that reported previously [25], and the FT1DM patients showed a significant decline of AGI compared with T1ADM patients in the HbA 1c ≤ 7:0% subgroup. Based on the results mentioned above, we found that if we added HbA 1c to AGI, then diagnosing FT1DM at AGI ≤ 0:3 and HbA 1c ≤ 7:0% accurately distinguished 86.57% of individuals, with its differential diagnostic efficacy of combined criteria increasing by 61.11% when compared with AGI only, and providing a basis for early identification and therapy.
The current study enrolled participants with non-DM, FT1DM, T1ADM, LADA, and T2DM simultaneously and can better define the clinical features of diabetic and non-DM subjects as well as different subtypes of diabetes patients to provide evidence for clinical diagnosis and therapy. However, there are still some limitations. First, the sample size was relatively small because of the low incidence of FT1DM. Second, this was a cross-sectional study, so further prospective studies are needed to verify the efficacy of AGI and HbA 1c combined criteria in the differential diagnosis of FT1DM and T1ADM with HbA 1c < 8:7%.
In summary, this study proposed the glucose monitoring parameter AGI for the first time and found that AGI can be used for the early differential diagnosis of FT1DM and T1ADM with HbA 1c < 8:7%, with an optimal cut-off point for AGI of 0.3.