Blood Sugar Monitoring: How, When, and Why to Check Your Glucose
Updated: 6 days ago
Written and medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026 · How we review
Quick Answer: What is blood sugar monitoring?
Blood sugar monitoring is checking your glucose with a glucose meter and finger stick or a continuous glucose monitor (CGM) to see how well your diabetes plan is working. For most nonpregnant adults with diabetes, targets are 80–130 mg/dL before meals and under 180 mg/dL 1–2 hours after a meal starts; below 70 mg/dL is low. [1]
What the research says
CGMs improve control even without intensive insulin. A 2026 review of 25 randomized trials in adults with type 2 diabetes found CGM use lowered A1C by about 0.34 percentage points and added roughly 7.9% more time in the target range each day (Al Hayek et al., J Diabetes Sci Technol, 2026).
Finger-stick checks help people who don't take insulin. Across 22 trials with 6,204 people with type 2 diabetes not on insulin, self-checking lowered A1C by 0.30 points. Checking 8–11 times a week gave the best result (−0.35 points) (Zou et al., J Gen Intern Med, 2023).
Checking during pregnancy protects the baby. In gestational diabetes, self-checking compared with routine clinic checks cut the risk of a large-for-age baby by 40% (2,719 women) and of a very heavy newborn (macrosomia) by 50% (Burk et al., Pregnancy, 2025).
Key takeaways
Checking your blood sugar tells you how food, activity, medicine and daily life affect your levels.
You can use a glucose meter, a CGM, or both.
Checking matters most if you take insulin, are pregnant, are sick, or have frequent lows.
Your numbers are information, not a grade.
Common blood sugar target ranges for nonpregnant adults with diabetes. Image: Rinnit.com
Why does blood sugar monitoring matter?
Blood sugar monitoring matters because your glucose can change by the day and sometimes by the hour, and checking it shows whether your current treatment is working.
Your results help you make everyday decisions about:
What and when to eat
How much to exercise
How much insulin to take, if you use it
Monitoring is especially important for people with type 1 diabetes and anyone who takes insulin.
What makes blood sugar go up or down?
Some changes are easy to predict with practice. Others are hard or impossible to predict. That is why regular checks matter.
Usually raises blood sugar | Usually lowers blood sugar | Can go either way |
Eating carbohydrates | Skipping meals | Menstrual periods |
Missing or taking too little diabetes medicine or insulin | Taking too much diabetes medicine or insulin | Timing of food and medicine |
Less activity than usual | Physical activity | Drinking alcohol |
Steroid (corticosteroid) medicines | Other medicines interacting with diabetes treatment | |
Illness, surgery or stress | ||
Early-morning hormone rise (dawn phenomenon) | ||
Smoking, dehydration, puberty |
Morning numbers higher than expected? Read about why morning blood sugar can spike.
What are the two ways to check blood sugar at home?
Blood sugar can be checked at home with a glucose meter and finger stick, or with a continuous glucose monitor (CGM).
1. Glucose meter and finger stick
This is the most common method. You prick the side of your fingertip with a tiny needle (a lancet), place the drop of blood on a test strip, and the meter shows your number within seconds.
Each check shows your blood sugar at one moment only. People who take insulin often need to check several times a day.
Meters and strips are sold at pharmacies, by mail order, or through your provider. Your provider can help you choose a meter.
2. Continuous glucose monitor (CGM)
A CGM is a small wearable device. A tiny sensor sits just under your skin and measures glucose in the fluid between your cells, 24 hours a day.
The device turns these readings into a graph, so you see how your levels change over time. Most CGMs can sound an alarm when your glucose runs too low or too high. Some connect to insulin pumps.
Important: CGMs can fail or give wrong readings. Do a finger-stick check if your CGM number doesn't match how you feel, or if it shows an error.
Meter vs. CGM at a glance
Feature | Glucose meter | CGM |
How it reads | Drop of blood from a finger stick | Sensor under the skin |
What you see | One number at one moment | Continuous readings and trend graph |
Alerts for highs and lows | No | Most models, yes |
Finger sticks needed | Every check | Sometimes, to confirm odd readings |
Training | Follow the meter's manual | Training on inserting the sensor and using the system |
Cost | Ongoing cost of test strips | Device and sensors; coverage varies |
Your choice often depends on cost, insurance coverage, your type of diabetes, how often you need to check, and your overall health. Many people use both.
How do you check your blood sugar with a meter?
Checking your blood sugar with a meter takes four steps: wash your hands, insert a test strip, prick the side of your fingertip and touch the strip to the blood drop.
How to check your blood sugar with a glucose meter. Image: Rinnit.com
Wash your hands. Food on your fingers can change the result. No soap and water? Use an alcohol wipe on your fingertip.
Insert a test strip into the meter.
Prick the side of your fingertip with the lancing device. Squeeze gently or try another finger if you don't get enough blood.
Touch the edge of the strip to the blood drop and wait. Your number appears on the screen.
Every meter is a little different, so check your user manual.
Keep a record
Most meters save your results, and many work with a phone app. No smartphone? Write down the date, time, number, and notes such as "before lunch" or "after a walk." Bring your meter, phone or log to every appointment. CGM data is saved automatically, and your provider can view it.
When should you check your blood sugar?
Check your blood sugar whenever you feel symptoms of low or high blood sugar, and on waking, before meals, 2 hours after a meal starts, around exercise and at bedtime, especially if you take insulin.
The best times of day to check your blood sugar. Image: Rinnit.com
Time | Why it helps |
On waking (fasting) | Shows how your levels behaved overnight, especially when compared with a bedtime check |
Before meals | Helps plan the meal and, if you use insulin, your dose |
2 hours after a meal starts | Shows how food affects you and whether doses need adjusting |
Before and after exercise | Activity usually lowers glucose but can raise it; checking catches both |
At bedtime | Catches lows that could go unnoticed during sleep, and highs that would stay up for hours overnight |
How often should you check?
There's no single rule. It depends on your type of diabetes, your medicines, your health, and your daily routine. Your provider will suggest a schedule.
You may need to check more often if you:
Take insulin
Are pregnant
Have trouble reaching your targets
Have frequent low blood sugar
Have lows without the usual warning signs
Are sick or just had surgery
What do your blood sugar numbers mean?
Blood sugar numbers show whether you are in your target range, low (below 70 mg/dL) or high (above 180 mg/dL).
Target ranges
Your targets are personal and may change over your life. For most nonpregnant adults with diabetes, common targets are:
When you check | Common target |
Before a meal | 80–130 mg/dL |
1–2 hours after a meal starts | Under 180 mg/dL |
On waking and at bedtime | Set individually by your provider |
Your provider may set different targets based on:
How long you've had diabetes
Your age and life expectancy
Heart disease or diabetes complications (nerve, eye or kidney damage)
Conditions that affect blood sugar, such as Cushing syndrome or gastroparesis
Not feeling low blood sugar symptoms (hypoglycemia unawareness)
Pregnancy or planning a pregnancy
Access to medicines and technology
Low blood sugar: below 70 mg/dL
Most people with diabetes feel symptoms of low blood sugar (hypoglycemia) under 70 mg/dL. Early signs include:
Weakness or dizziness
Intense hunger
Shaking or trembling
Sweating
Pounding heart
Feeling scared or anxious
Check your number when these appear, because how low you are guides treatment. Low blood sugar is treated with 15 grams of fast sugar, such as glucose tablets or half a cup of juice or regular soda, then rechecking after 15 minutes. Severe lows can be life-threatening.
High blood sugar: above 180 mg/dL
For people with diabetes, readings above 180 mg/dL are usually considered high (hyperglycemia). Most people don't feel symptoms until about 250 mg/dL or higher. Watch for:
More thirst or hunger
Peeing more often
Headache
Irritability
Blurry vision
If you use insulin, treat highs as your provider has instructed. High blood sugar with vomiting and tiredness can signal diabetic ketoacidosis (DKA) — a life-threatening emergency.
What are the downsides of blood sugar monitoring, and how can you manage them?
The main downsides of blood sugar monitoring are sore fingertips, cost, and frustration or worry, and each one can be eased.
Challenge | What helps |
Sore fingertips | Prick the sides, not the pads (fewer nerve endings). Use a fresh lancet; reused ones get dull. Newer strips need less blood, and newer lancets hurt less. Some meters allow testing on the palm or forearm. |
Cost | Ask your provider about lower-cost options. Some pharmacies offer coupons, and community programs may help with supplies. Check what your insurance covers. |
Frustration or worry | Remember, a number is not a judgment. Many things affect blood sugar, and some can't be predicted. If negative feelings keep coming back, talk to your provider or a mental health professional. Depression and anxiety are common with diabetes. |
When should you call your doctor or get emergency help for blood sugar readings?
Call your provider if you keep getting high or low blood sugar readings or symptoms, and get emergency care for signs of DKA or a severe low with unresponsiveness. This applies to both type 1 and type 2 diabetes, and your plan may need adjusting.
Get emergency care if:
You have signs of DKA — call your provider right away or go to the nearest emergency room.
Someone with diabetes has a severe low and is unresponsive or unconscious — call emergency services immediately.
Questions to ask at your next visit
What is my target range, and why?
How often should I check?
Should I use a meter, a CGM, or both?
What do different numbers mean for me?
What changes should we make to my plan?
Conclusion
Blood sugar monitoring turns guesswork into clear information. A meter shows a snapshot, while a CGM shows the whole story. Knowing when to check — on waking, around meals and exercise, at bedtime, and whenever you feel off — helps you and your care team fine-tune your treatment and lower your risk of complications. Treat each reading as a tool, not a test you pass or fail.
Take the next step: Save or print this guide and bring your questions to your next appointment. Then build your knowledge with our complete guide to diabetes and our guides to prediabetes and gestational diabetes. Explore more trusted, doctor-reviewed health guides on Rinnit.com.
Frequently asked questions
What is a normal blood sugar target for adults with diabetes?
For most nonpregnant adults with diabetes, a common target is 80–130 mg/dL before meals and under 180 mg/dL one to two hours after a meal starts. Your provider may set different numbers for you.
What blood sugar level is too low?
Below 70 mg/dL is considered low for most people with diabetes. Treat it with fast sugar, such as juice, and seek help if symptoms are severe.
What blood sugar level is too high?
Above 180 mg/dL is usually considered high. Many people don't notice symptoms until about 250 mg/dL or higher, so regular checks matter.
When is the best time to check my blood sugar?
Useful times are on waking, before meals, two hours after a meal starts, before and after exercise, and at bedtime — plus any time you feel symptoms.
How often should I check my blood sugar?
It depends on your diabetes type, medicines, and health. People who take insulin, are pregnant, are sick, or have frequent lows usually need to check more often.
Can a CGM replace finger sticks completely?
Not always. CGMs can fail or be inaccurate. Use a finger stick if a reading doesn't match your symptoms or the device shows an error.
How can I make finger sticks hurt less?
Prick the side of your fingertip, use a new lancet each time, and ask about newer lancets or meters that allow testing on the palm or forearm.
Why are my morning blood sugar numbers high?
One common reason is the dawn phenomenon — a natural early-morning rise in hormones such as cortisol that pushes glucose up. Checking at bedtime and on waking helps your provider spot it.
Why should I wash my hands before checking my blood sugar?
Food or sugar on your fingers can give a falsely high result. Wash with soap and water, or use an alcohol wipe if you cannot wash.
What should I do if my blood sugar is low?
Eat or drink 15 grams of fast sugar, such as glucose tablets or half a cup of juice or regular soda, then recheck in 15 minutes. Call 911 if the person passes out, has a seizure or cannot swallow safely.
Related reading on Rinnit.com
References
Cleveland Clinic. Blood Sugar Monitoring: Why, How & When To Check. Cleveland Clinic. Last updated January 3, 2023. https://my.clevelandclinic.org/health/treatments/17956-blood-sugar-monitoring
National Institute of Diabetes and Digestive and Kidney Diseases. Managing Diabetes. NIDDK, National Institutes of Health. Last reviewed October 2023. Accessed October 20, 2026. https://www.niddk.nih.gov/health-information/diabetes/overview/managing-diabetes
Mathew TK, Zubair M. Blood Glucose Monitoring. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated April 12, 2026. PMID: 32310436. https://pubmed.ncbi.nlm.nih.gov/32310436/
Al Hayek A, Al Zahrani WM, Alotaibi HF, et al. Effectiveness of continuous glucose monitoring in non-intensively managed type 2 diabetes: a systematic review and meta-analysis of randomized controlled trials. Journal of Diabetes Science and Technology. 2026. Epub ahead of print October 14, 2026. PMID: 42872823. https://doi.org/10.1177/19322968261489265
Zou Y, Zhao S, Li G, Zhang C. The efficacy and frequency of self-monitoring of blood glucose in non-insulin-treated T2D patients: a systematic review and meta-analysis. Journal of General Internal Medicine. 2023;38(3):755-764. PMID: 36403159. https://doi.org/10.1007/s11606-022-07864-z
Burk J, Sweeting A. Glucose monitoring in the management of diabetes in pregnancy: a systematic review and meta-analysis. Pregnancy (Hoboken). 2025;2(1):e70214. PMID: 42597232. https://doi.org/10.1002/pmf2.70214
Medical disclaimer
This article is for education and does not replace advice from your healthcare provider. Always seek the advice of your doctor or another qualified health provider with any questions about a medical condition or treatment.
Comments