Continuous Glucose Monitors (CGMs) vs Finger-Prick Testing

Monitoring blood glucose isn’t busywork — it’s what keeps you safe and gives you agency. Two tools dominate: the finger‑prick meter and the continuous glucose monitor (CGM). They serve different purposes and, used together, cover each other’s blind spots.

Finger‑Prick Testing (BGM)

What it is: a capillary blood test from the fingertip (or alternate site), giving a single reading.

Strengths

Accurate “now” value with ISO‑standard meters.
Low cost and no warm‑up, works anywhere.
Not affected by most compression or sensor warm‑ups.

Limitations

No trends or alerts — it’s a snapshot.
Can miss overnight lows or rapid swings between checks.

Where it shines

Confirming CGM readings during rapid change.
Pre‑driving, pre‑exercise, illness/sick days.
Troubleshooting: “Is my CGM right?” → do a meter check.

Continuous Glucose Monitors (CGMs)

What it is: a small sensor under the skin measuring interstitial glucose every 1–5 minutes, streaming to a phone/reader; many offer alarms.

Strengths

24/7 visibility: graphs, trend arrows, time‑in‑range.
Alerts for highs/lows — especially valuable overnight.
Enables smarter dosing (pre‑bolus timing), exercise planning, and learning patterns.

Limitations

Lag vs blood during rapid rises/falls (interstitial fluid delay).
Warm‑up periods, adhesive issues, occasional sensor failures.
Cost; availability and subsidy vary by country.

Where it shines

Preventing severe hypos, spotting patterns, refining basal/bolus strategy.
Powering AID (automated insulin delivery) with compatible pumps.

CGM vs Meter: How to Combine

Think of CGM as the weather radar (direction + speed), and the meter as looking out the window (ground truth).

Use CGM day‑to‑day for trends, alerts, and learning.
Use meter to confirm when:
- Symptoms don’t match CGM.
- Reading changes very fast (double‑arrow up/down).
- First 12–24 h of a new sensor feels “off”.
- Before driving if you’re unsure.
If high with ketones (or unwell): rely on meter readings and follow your sick‑day plan.

Practical Moves

Pre‑bolus: aim insulin before the CGM line climbs; faster insulins may shorten the gap.
Compression lows: unexpected CGM low while lying on the sensor? Sit up, wait, or finger‑prick confirm.
Sensor adhesion: use over‑patches/skin prep; rotate sites to avoid irritation.
Data sanity: watch time‑in‑range (TIR), GMI, and coefficient of variation (CV) — not just single numbers.

Safety Notes

Treat hypos first; debate accuracy later.
For pump users: if high + ketones, inject correction by pen/syringe and change infusion set.
Don’t ignore alarms at night; adjust thresholds if they’re too noisy, not off.

References (plain text)