Table 5.

Attributes of current monitoring methods

Method	Pros	Cons	Metrics obtained
Reference OGTT*	Gold standard in research settings Used to stage disease and predict progression	Requires glucose load and 2–5 blood draws over 2 h	Glycemic staging Risk scores for progression (DPTRS, DPTRS60, Index60, M60, M120, PLS) (94,165–169)
Standard OGTT†	Similar to test for GDM: OGTT with 2 × blood draws (compared with 3 × draws in GDM test), performed routinely in clinical care	Requires 2 blood draws: fasting and at 2 h	120-min OGTT-derived glucose M120
Random glucose	One-off sample Low cost	Requires a blood draw or fingerstick test Less sensitive than 120-min OGTT	Similar to 120-min OGTT-derived glucose (96) if obtained 2 h postprandially
Standard HbA1c test	Highly specific for clinical diagnosis of stage 3 T1D Can use capillary sample Longitudinal HbA1c may be as informative as OGTT (66)	Indicates 3-month mean glucose. Often normal in asymptomatic or recent-onset stage 3 T1D May be affected by age, nondiabetes disease states (e.g., renal, hematological syndromes) Not suitable in the home setting	Risk of progression to “clinical disease”: HbA1c >39 mmol/mol (>5.7%) (170) 10% rise from baseline (at first positive islet autoantibody) over 3–12 months (66,67) suggests dysglycemia and progression to stage 2 T1D Consider use of CGM if 10% rise in HbA1c is confirmed, or higher frequency of SMBG, to monitor risk for progression
CGM‡	Can be used at home Can be blinded for physician review only in some regions Optimal duration of CGM wear is validated in adults and children >2 years of age with diagnosed T1D, at all glycemic levels (171)	Risk of anxiety for unblinded user seeing CGM fluctuations and experiencing alarms Requires appropriate education on use and interpretation Many primary care HCPs are unfamiliar with interpretation Cost and access issues Duration of wear not validated in early-stage T1D	Sensitive in detecting individuals with asymptomatic stage 3 T1D and dysglycemia in stage 2 T1D (73) Risk of progression to “clinical disease,” i.e., 10% of time with glucose >7.8 mmol/L (>140 mg/dL) has been associated with an 80% risk of progression to T1D within 12 months (72) ≥5% time with glucose ≥7.8 mmol/L (≥140 mg/dL) has been associated with a 40% risk of progression to T1D within 2 years (71) Other PPV metrics not tested
SMBG	Simple to use at home Comparatively low cost	Uncomfortable for users, can affect accuracy and use Optimal timing and frequency have not been determined	Immediate capillary blood glucose test result 2-h postprandial measure likely of most value
C-peptide	Validated measure of β-cell function Stimulated C-peptide in research settings is valuable to assess insulin production and distinguish between T1D (or stages of T1D) and T2D	Can be falsely low in hypoglycemia <3.9 mmol/L (<70 mg/dL), in severe hyperglycemia/DKA or after fasting, so concomitant serum glucose should be checked for interpretation Wide range of values at clinical diagnosis, including >0.2 nmol/L, and persistent, but low, levels of secretion can be seen long after diagnosis Presence of C-peptide does not exclude T1D and on its own is not useful for staging or diagnosis of T1D	A stimulated postprandial C-peptide value ≤0.2 nmol/L with IAb+ status can assist with appropriately classifying diabetes type
Repeat antibody testing	Confirms initial IAb+ test result and progression to multiple IAb+ status	None	Autoantibody type and single IAb+ or multiple IAb+ status
Education	Provides awareness of diabetes symptoms and signs	None	Person-reported outcomes for possible progression to stage 3 T1D

DPTRS, Diabetes Prevention Trial-Type 1 risk score; GDM, gestational diabetes mellitus; M60, 60 min test result; M120, 120 min test result; PLS, partial least squares; PPV, positive predictive value; T1D, type 1 diabetes; T2D, type 2 diabetes.

^*Used in research settings for staging progression of impaired glucose tolerance as C-peptide provides important predictive value.

^†Used in clinical practice to detect impaired glucose tolerance in prediabetes and gestational diabetes mellitus.

^‡Use of CGM-derived criterion did not achieve consensus within the consensus panel, with further evidence required to confirm findings to date.