Assess use of SMBG to calibrate CGM system

STEP 1 — Gather Information

Collect: CGM device model and calibration requirements (e.g., every 12 hours, twice daily), patient’s self-reported SMBG frequency and timing, recent SMBG log, understanding of calibration purpose, any barriers (e.g., pain, cost, forgetfulness), and whether calibrations are performed during stable glucose periods (not during rapid changes or after meals/exercise).

STEP 2 — Rule In / Rule Out

Does the patient perform SMBG calibrations at the frequency and timing specified by the CGM manufacturer?

• Yes → Rule in adequate calibration practice.
• No → Rule out inadequate calibration practice.

STEP 3 — Classify or Stratify

Classify calibration adequacy:

• Adequate: calibrations performed per schedule, with proper technique (hand washing, fingertip sample, stable glucose).
• Suboptimal: calibrations missed occasionally or performed at incorrect times (e.g., during rapid glucose excursions).
• None: no calibrations performed or reliance on alternative site testing without validation.

STEP 4 — Decide

• If adequate: reinforce technique, remind of importance, and continue routine follow‑up.
• If suboptimal: provide targeted education on calibration schedule and technique, set reminders, and re‑assess in 1–2 weeks.
• If none: initiate hands‑on training, consider switching to a factory‑calibrated CGM if available and appropriate, and ensure patient understands that SMBG remains necessary for calibration verification.

Clinical Guardrails / Mimics / Pitfalls

Do not assume CGM accuracy without calibration; avoid calibrating during hypoglycemia, hyperglycemia, or within 30 minutes of meals/exercise; do not use alternative site (e.g., forearm) SMBG for calibration unless validated; never skip calibrations based on sensor “feel” of accuracy; and recognize that inadequate calibration can lead to missed alerts and erroneous insulin dosing.

Concrete Clinical Example

A 58‑year‑old with T1D using Medtronic Guardian RT‑CGM reports checking glucose 4 times daily but admits skipping morning calibrations when rushed. Assessment shows calibrations performed only 3–4 times weekly. After education on twice‑daily calibration and setting phone alarms, compliance improves to 90% over two weeks, reducing unexplained CGM‑SMBG discrepancies.

Source: Diabetes Technology—Continuous Subcutaneous Insulin Infusion Therapy and Continuous Glucose Monitoring in Adults: An Endocrine Society Clinical Practice Guideline, Endocrine Society, 2016, DOI: 10.1210/jc.2016-2534