1. Chapter Overview: The "Language" Update
The 2021 update fundamentally changed the vocabulary of glucose monitoring. The CDE exam will likely test your knowledge of these new terms and the specific indications for each technology.
CBG (Capillary Blood Glucose): Formerly “SMBG.” The traditional finger-stick method.
isCGM (Intermittently-Scanned CGM): Formerly “Flash” (e.g., FreeStyle Libre). Requires scanning to see data.
rtCGM (Real-Time CGM): (e.g., Dexcom, Medtronic). Continuously pushes data to a device/phone with alarms.
mCGM (Masked CGM): Formerly “Professional CGM.” Data is hidden from the patient and analyzed retrospectively by the clinician.
2. Key Messages (The "Gold Nuggets")
A1C Limitations: A1C is a retrospective average (last 2–3 months) and cannot detect daily hypoglycemia or glycemic variability.
A1C Weighting: 50% of the A1C value comes from the last 30 days.
Monitoring is Not Treatment: Monitoring devices (CBG, isCGM, rtCGM) do not lower A1C on their own; they must be paired with education and therapeutic action.
Pregnancy: rtCGM is now the standard of care for Type 1 diabetes in pregnancy to improve neonatal outcomes.
3. A1C Testing
Frequency: Measure every 3 months when targets are not met or therapy is adjusted. Consider every 6 months if stable.
Limitations: A1C may be inaccurate in conditions affecting red blood cell turnover (e.g., iron deficiency anemia raises A1C; hemolysis lowers A1C).
Point-of-Care A1C: Not approved for diagnosis of diabetes in Canada, only for monitoring.
4. Glucose Monitoring Technologies
A. Real-Time CGM (rtCGM)
How it works: Pushes data continuously; has alarms for highs/lows.
Benefits (Type 1):
Reduces A1C and increases Time in Range (TIR).
Reduces duration and incidence of hypoglycemia.
Reduces severe hypoglycemia in those with impaired awareness.
Benefits (Type 2): May be used to improve glycemic levels in those on basal-bolus insulin.
Pregnancy (Type 1): Should be used. Reduces Large for Gestational Age (LGA) infants, neonatal hypoglycemia, and NICU admissions >24 hours (CONCEPTT trial).
B. Intermittently-Scanned CGM (isCGM)
How it works: User must scan sensor to see data; no automatic alarms (in older versions).
Benefits:
Reduces time spent in hypoglycemia for Type 1 and Type 2 (on insulin).
Increases Time in Range (TIR).
Note: Does not consistently reduce A1C in trials compared to CBG, but improves other metrics.
Comparison to rtCGM: rtCGM is superior for reducing hypoglycemia and fear of hypoglycemia in high-risk Type 1 patients (impaired awareness).
C. Capillary Blood Glucose (CBG)
Insulin Users: Essential for self-management. Test at least 3 times/day for those on multiple injections.
Non-Insulin T2D:
Daily testing is not recommended if targets are met and meds don’t cause hypo.
Structured Testing: (e.g., 7-point profiles) is beneficial when A1C is off-target to guide therapy changes.
Pregnancy (GDM):
Initial: 4x daily (fasting + post-meals) for 1 week.
Diet-controlled: Can reduce to 4x daily on alternate days.
Insulin-treated: Continue 4x daily.
5. Glucose Metrics & Targets (The "New Numbers")
The 2021 Update emphasizes “Time in Range” (TIR) alongside A1C.
6. 2021 Clinical Practice Guidelines Recommendations
Key Recommendations to Memorize:
Type 1 & rtCGM: rtCGM should be used to reduce A1C, increase TIR, and reduce hypoglycemia in adults/children willing to use it daily. (Grade A, Level 1A).
Type 1 & isCGM: isCGM may be used to increase TIR and reduce hypoglycemia. (Grade B, Level 2).
Hypo Awareness: In adults with T1D and impaired awareness, rtCGM is recommended over isCGM to reduce time in hypoglycemia. (Grade B, Level 2).
Pregnancy (T1D): rtCGM should be used to reduce risk of LGA infants and NICU admissions. (Grade A, Level 1A).
Ketones: T1D patients should test for ketones during acute illness or if BG >14.0 mmol/L. Blood ketone testing is preferred over urine. (Grade B, Level 2).