Blood Sugar Monitoring at Home: Meters, Continuous Monitors, and Strips

Home glucose monitoring used to mean one thing: a fingerstick meter. It now means three, and the newest option is being sold to people who do not have diabetes at all. Here is how they compare and what each one is for.

Fingerstick meters

A drop of blood from a lancet on a test strip, read by a small meter. Results in five seconds. This is the standard for people with diabetes who take insulin, because the number it gives is the number now, and insulin doses depend on it.

Accuracy. FDA standards allow meters to be within 15 percent of a lab value 95 percent of the time. In practice good meters do better. A reading of 100 could be anywhere from 85 to 115 by the rule, and is usually within 5 to 10.

Best for. Anyone on insulin. Anyone with diabetes who needs to check fasting and after meal values on a schedule. Anyone confirming a symptom, such as shakiness that might be low blood sugar.

Cost. Meters are cheap or free. Strips are the ongoing cost and vary widely. Insurance usually covers a set number per month with a diagnosis.

Technique matters. Wash hands first; fruit residue on a finger reads as sugar. Use the side of the fingertip, not the pad. Do not squeeze hard; tissue fluid dilutes the sample. Use the strips within their expiration and keep the vial closed.

Continuous glucose monitors

A small sensor with a filament under the skin, worn on the arm or abdomen for 10 to 15 days, reads glucose in the fluid between cells every few minutes and sends it to a phone or reader. Two brands now sell versions over the counter without a prescription, aimed at people without diabetes.

What it measures. Interstitial fluid, not blood. Interstitial glucose lags blood glucose by several minutes, more when it is changing fast. After a meal, the CGM is a few minutes behind. During a rapid drop, it can be noticeably behind and can miss the low.

Accuracy. Modern sensors have mean errors around 8 to 10 percent against a lab. Good enough to trend, good enough to dose insulin from for most people with diabetes, and approved for that use. Individual readings can be off, particularly in the first day of a sensor and at the extremes.

Best for. Anyone with type 1 diabetes. Anyone with type 2 on insulin or with frequent lows. Anyone whose clinician wants to see patterns rather than points.

For people without diabetes. The over the counter sensors are marketed for "metabolic awareness." They will show you that white bread spikes glucose and a walk after dinner blunts it. That is real and some people find it motivating. What the sensor cannot do is diagnose anything. Glucose in a healthy person swings within a normal range, and the apps often flag normal swings as events. Two weeks of it is an education. Months of it, for a healthy person, mostly generates anxiety about numbers that do not need managing. If you use one, know the normal range for a nondiabetic: rarely above 140 after meals, back under 100 within two to three hours, and fasting under 100.

Cost. Sensors cost several times a month of strips. Covered by insurance for diabetes on insulin in most plans, increasingly for type 2 without insulin, and not at all for people without diabetes.

Urine glucose strips

The glucose pad on a urine strip detects sugar spilling into urine when blood glucose passes the kidney threshold, roughly 180 mg/dL. See glucose in urine.

What it tells you. That blood sugar was above the threshold at some point in the hours the urine was made. Nothing more precise than that.

Best for. A rough screen in someone without diabetes who wants to check now and then. A positive means get a blood test. A negative means blood sugar has not been above 180 recently, which is reassuring but not the same as normal.

Not for. Managing diabetes. It cannot detect low blood sugar, cannot give a number, and lags by hours. Meters replaced it for this purpose decades ago.

A1C at home

Not a monitor, but worth placing. A1C is a three month average. Home fingerstick A1C kits and mail in tests exist and are reasonably accurate. One every three to six months is a reasonable check for someone with prediabetes. It complements the tools above rather than replacing them. See diabetes screening explained.

Which one, in one line each

Insulin: a meter, and a CGM if it is covered. Type 2 without insulin: a meter for periodic fasting and after meal checks, or a CGM for a few weeks to learn patterns. Prediabetes: a home A1C every few months, a meter for the occasional fasting reading, and a CGM only if you understand it is a teaching tool. No diabetes, curious: a urine strip or an occasional meter reading. A CGM if you want the education and can ignore the alarms.

What a reading should change

A single high reading changes nothing except a plan to recheck. A pattern changes things. Fasting readings creeping up over months, after meal readings staying high longer, a CGM showing more time above 140. Those go to a clinician with the log. The value of home monitoring is the record, not the moment.