A useful blood sugar log records each reading with its time, unit and meal timing, plus the food, medicine, activity, illness and stress around it. Here is how often guidelines suggest checking, how paired testing works, and how to read one to two weeks of entries for patterns.
A blood sugar log is most useful when every reading is written down with its date, time and unit, whether it came before or after a meal, and what you ate, which medicines you took and how active you were 1, 2. How often to check depends on your treatment: Diabetes Canada recommends at least three checks a day, including before and after meals, for people who take insulin more than once a day 4.
Single readings are noisy. A week or two of entries, read side by side, shows what repeats. The American Diabetes Association (ADA) says the best use of a meter requires review and interpretation of the data by both the person with diabetes and their health care professional 9.
Glucose here is in mmol/L with mg/dL in brackets; see mmol/L and mg/dL to convert.
Every entry needs the date, the time and the reading, plus medicines and doses, and diet and exercise information, according to Mayo Clinic 1. The US Centers for Disease Control and Prevention (CDC) suggests keeping notes about anything that might have affected a reading 10.
The ADA calls a reading below 3.9 mmol/L (70 mg/dL) but at or above 3.0 mmol/L (54 mg/dL) level 1 hypoglycemia (low blood sugar), and below 3.0 mmol/L level 2. Level 3 is a severe event in which the person needs someone else’s help to recover, whatever the number 5. See low blood sugar for warning signs and treatment.
In plain terms: The number tells you how high or low your glucose was. The notes beside it tell you, and your care team, why. A high reading after a large dinner and the same reading during a fever mean different things.
It depends mostly on how your diabetes is treated, and your doctor will tell you when and how often to check 10.
Diabetes Canada recommends at least three checks a day, including before and after meals, for people with type 1 or type 2 diabetes who take insulin more than once a day. With once-daily insulin plus other glucose-lowering medicines in type 2 diabetes, it recommends at least one check a day at variable times 4.
The ADA’s 2026 Standards of Care say checks for people on insulin may include fasting, before meals and snacks, after meals, at bedtime, in the middle of the night, around exercise, when a low or a high is suspected, after treating a low until glucose is back to normal, and before and while driving or doing other critical tasks 9. Mayo Clinic notes that with type 1 diabetes, a care team may suggest a continuous glucose monitor (CGM), a sensor worn on the skin, or checks 4 to 10 times a day 1.
For type 2 diabetes without insulin, Diabetes Canada says frequency should be individualized by medicine type, glucose control and risk of lows. When targets are not being met, it recommends checking with periodic before- and after-meal readings; when targets are met, or the medicines don’t cause lows, infrequent checks are appropriate 4. The ADA notes that meter checks on noninsulin treatment have not consistently lowered A1c (a blood test that reflects average glucose over recent months; see A1c, GMI and average glucose) by a clinically significant amount, but may help while meal plans, activity or medicines are being changed, as part of a treatment adjustment program 9.
Mayo Clinic lists being sick, a change in routine and starting a new medicine 1, and Cleveland Clinic stresses checking when you have symptoms of a low or a high 3. During illness, the CDC advises testing every 4 hours and keeping track of the results. It says to go to the emergency room right away if, among other signs, you have trouble breathing, can’t keep liquids down for more than 4 hours, or your blood sugar is lower than 3.3 mmol/L (60 mg/dL) 12. Diabetes Canada recommends ketone testing in type 1 diabetes during an acute illness with high glucose, when before-meal readings stay above 14.0 mmol/L (252 mg/dL), or with symptoms of diabetic ketoacidosis, a dangerous complication of high blood sugar 4.
Most logs are built around five moments: fasting, before meals, after meals, bedtime and, now and then, the middle of the night 9. After-meal readings are timed from the start of the meal: the ADA says 1 to 2 hours after the beginning of the meal 5, Cleveland Clinic gives the same window 3, and Diabetes Canada uses 2 hours 6.
| Check | ADA goal, many nonpregnant adults | Diabetes Canada target, most adults |
|---|---|---|
| Fasting and before meals | 4.4–7.2 mmol/L (80–130 mg/dL) 5 | 4.0–7.0 mmol/L (72–126 mg/dL) 6 |
| After meals | Peak below 10.0 mmol/L (180 mg/dL), 1–2 hours after the start 5 | 5.0–10.0 mmol/L (90–180 mg/dL) at 2 hours 6 |
| Bedtime and overnight | No general goal in the table 5 | No separate target 6 |
If A1c stays above target, Diabetes Canada says 4.0 to 5.5 mmol/L (72 to 99 mg/dL) fasting and 5.0 to 8.0 mmol/L (90 to 144 mg/dL) after meals may be considered, balanced against the risk of lows. Its first recommendation is that targets should be individualized 6. Targets for pregnancy, children and older adults are in normal blood sugar levels.
With no general bedtime number, a bedtime target is one to set with your care team. Mayo Clinic lists checking before bed, and sometimes during the night, with type 1 diabetes 1. A bedtime reading beside the next fasting reading shows whether glucose climbs overnight; see the dawn phenomenon.
Paired testing means checking just before a meal and again 1 to 2 hours after you start eating, so the difference shows how that meal, and any medicine taken with it, affected your glucose 5. Structured testing is a planned set of such checks over a few days, recorded so that patterns are easy to see. Pairs also show why the same meal can spike differently.
The best-known trial is the Structured Testing Program (STeP) study in Diabetes Care. It followed 483 adults with type 2 diabetes who did not use insulin and had an A1c of 7.5% or higher, at 34 US primary care practices, for 12 months 7. The structured group recorded a seven-point profile, fasting, before and 2 hours after each meal, and at bedtime, on 3 days in a row before each study visit, on a paper tool that plotted the readings. Their doctors and staff were trained to interpret the results. The comparison group received enhanced usual care, including free meters and strips 7.
After a year, A1c had fallen by 1.2% in the structured group and 0.9% in the comparison group, a difference of 0.3% (P = 0.04). Among people who followed the protocol, the drops were 1.3% and 0.8%. At the first visit, doctors recommended a treatment change for 75.5% of the structured group against 28.0% of the comparison group 7.
The ADA notes that for people with type 2 diabetes not taking insulin, the most benefit has been seen in structured clinical programs 9, and Diabetes Canada says monitoring is most effective when combined with an education program 4.
Compare the same time of day across several days instead of reacting to one number: a pattern is a result that repeats, such as a high before breakfast on most mornings. Cleveland Clinic notes that a record shows what makes your levels go up or down, such as different foods 3. The Johns Hopkins Diabetes Guide notes that meters usually store results by date and time, and some show averages over 7, 14 or 30 days 13.
A log with a column for each time of day lets you read down the before-breakfast column for the whole week. A fasting reading higher than bedtime on most nights points to something overnight. When an after-meal reading is much higher than its pair, the notes show what was different about that meal. For lows, look at what came before: Mayo Clinic notes that exercise can lower blood sugar up to a day later, and alcohol long after the last drink 11.
If your A1c doesn’t match your meter, Diabetes Canada recommends comparing the meter with a lab fasting glucose taken at the same time, and doing so at least once a year anyway 4. See A1c, GMI and average glucose for why the numbers can differ.
What to do about a pattern is a question for your care team. In STeP, doctors had a guide to treatment options linked to specific patterns 7, and the ADA says people should be taught how to use their readings to adjust food, activity or medicines to reach their goals 9. Changes to insulin or other medicines should follow the plan your team has given you.
A CGM estimates glucose every few minutes 14, so its summary report does most of the pattern-finding, and the log adds what the sensor can’t see: meals, doses, exercise, illness and treated lows. The ADA recommends CGM from diagnosis onward for people on insulin or on other medicines that can cause lows, and for anyone whose management it helps 9.
The ADA recommends that standardized reports, at minimum a single page such as the standardized CGM report and weekly summary, be available and used 9. The usual format is the ambulatory glucose profile (AGP), which the International Consensus on Time in Range calls the standardized AGP report 15; see how to read an AGP report.
The consensus bases the report on 14 days of data, with 70% of the possible readings captured. For most adults with type 1 or type 2 diabetes, its targets are more than 70% of readings between 3.9 and 10.0 mmol/L (70 and 180 mg/dL), less than 4% below 3.9 mmol/L (70 mg/dL), and less than 1% below 3.0 mmol/L (54 mg/dL). Each 5% increase in time in range is associated with clinically significant benefits, and 70% corresponds to an A1c of about 7% 15.
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) notes that many CGM apps let you track food, activity and medicines, and that you may sometimes need to compare a reading with a finger-stick test, for example when you doubt its accuracy 14. Logging those checks shows how far apart the two were. See CGM versus a meter.
Both work if they are complete and reviewed, and in trials, apps lowered A1c by about half a percentage point more than control groups in type 2 diabetes 8.
A 2016 meta-analysis in Diabetes Care pooled 14 randomized trials with 1,360 participants. In type 2 diabetes, app users lowered A1c by 0.49% more than control groups (95% confidence interval 0.30% to 0.68%), with evidence rated moderate quality. Younger people were more likely to benefit, and the effect was larger with feedback from a health care professional. There were not enough data to judge apps for type 1 diabetes 8.
Paper still has a place: the CDC notes that if you prefer not to use a phone, you can keep a written record 10. Many devices can send readings to a computer or smart device 1. If you’d like a paper log, our printable one-week blood sugar log (PDF) has rows for glucose, food or carbs, and insulin or medicine before and after each meal, at bedtime and overnight, with space for notes and a page on how to use it.
A 2021 BMJ study of 20,991 health and medical apps found that 88.0% contained code that could potentially collect user data and 28.1% had no privacy policy 16. The ADA calls online privacy and security “an area of particular importance” 9. Before logging in an app, it is worth checking where your data are stored, whether they are shared, and whether you can export and delete them. See how to choose a diabetes app.
Mayo Clinic advises bringing your record of results to checkups 1, and Cleveland Clinic suggests bringing your meter, phone or written record to each visit 3. UCSF suggests asking your provider whether they have a logbook or an electronic way to track this information 2. Some CGMs can also send readings to a second person’s smartphone, such as a parent, partner or caregiver 14.
It depends on your treatment. Diabetes Canada recommends at least three checks a day, including before and after meals, with insulin more than once a day. Without insulin, frequency is individualized, and infrequent checks are appropriate when targets are met or medicines don’t cause lows 4.
The date, time and reading, your medicines and doses, and your food and exercise 1. Also note whether it was before or after eating, and anything that might have affected it 3, 10.
The ADA times after-meal checks 1 to 2 hours after the start of the meal, with a peak goal below 10.0 mmol/L (180 mg/dL) for many nonpregnant adults 5. Diabetes Canada uses a 2-hour reading with a target of 5.0 to 10.0 mmol/L (90 to 180 mg/dL) 6.
A CGM records glucose every few minutes, but it can’t see what you ate, your doses or your activity. Many CGM apps let you track food, activity and medicines alongside the readings 14, and the standard summary report uses 14 days of data 15.
In a meta-analysis of 14 trials, apps lowered A1c by 0.49% more than control groups in type 2 diabetes, with a larger effect when a health professional gave feedback 8. A written record also works 10.
A log is easiest to read when every entry sits on one timeline. Glyve keeps glucose, food, insulin, exercise, sleep and stress together, and you can log by typing, by voice or with a photo of a meal, a nutrition label or a barcode; every estimate is a draft you check before saving. Glucose comes from Apple Health, from Dexcom and FreeStyle Libre through your own Dexcom Share or LibreLinkUp follower account (readings can arrive later than in the CGM’s own app), or from meter readings you type in, so a CGM isn’t required. You set your own target range, the daily glucose graph shows meals and doses beside the line, and the week view shows whether a pattern repeats. When you choose to share, Glyve exports a PDF summary, a CSV, an AGP report and a glucose graph with logged moments for your care team. Glyve is not a medical device; it gives no medical advice and recommends no insulin doses.
How we write about diabetes. Spotted a mistake? Email info@glyve.ca and we’ll check it against the source.
Glyve keeps glucose, food, insulin, exercise, sleep and stress on one timeline.
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