How to Read a Blood Sugar Log and What Normal Levels Look Like

A blood sugar log turns scattered glucose readings into a useful picture of how your body responds to food, movement, medication, stress and sleep. A single result can be informative, but repeated readings taken at similar times are much easier to interpret. In Australia, glucose is usually measured in millimoles per litre, written as mmol/L.

“Normal” depends on whether you have diabetes, are pregnant, take glucose-lowering medicine, or have another health condition. The numbers printed on a meter are not a diagnosis by themselves. Your GP, diabetes educator or endocrinologist can help match the results to your circumstances and treatment plan.

A clear record should show when the test was taken and what was happening around it. Recording breakfast, a walk, illness, a missed tablet or a stressful day can explain changes that would otherwise seem random. The aim is to recognise patterns safely, rather than chase every individual reading.

What to write in a glucose log

A useful entry includes the date, time, glucose result and whether the reading was taken before or after eating. If it was after a meal, note how long after the first bite: one hour and two hours can produce quite different results. Include medication doses, exercise, unusual snacks, alcohol and symptoms such as shakiness or sweating.

People using a continuous glucose monitor may record time in range, overnight trends and alerts alongside finger-prick checks. A CGM reading reflects glucose in the fluid between cells, so it can lag behind blood glucose when levels are changing quickly. If a sensor result does not match how you feel, follow the device instructions and consider a finger-prick check.

A paper notebook works well, while many meters and phone apps create graphs automatically. Use whichever system you will maintain. Someone in Melbourne might record a morning walk before work, while a person in rural Queensland may need to note a long drive, hot conditions or delayed meals. Those details can matter when a result looks unusual.

How timing changes the meaning of a result

A fasting reading is usually taken after an overnight fast, often before breakfast. For a person without diabetes, fasting glucose is commonly around 3.5–5.5 mmol/L, although laboratories and clinical guidelines may use slightly different cut-offs. A fasting result of 5.6 mmol/L or higher may need assessment, while a result of 7.0 mmol/L or above on repeat testing can indicate diabetes. Diagnosis requires appropriate clinical testing, not a home meter reading alone.

A pre-meal result shows the starting point before food affects glucose. A post-meal result shows the combined effect of the meal, insulin response, activity and medication. When reviewing a log, compare similar readings: breakfast before eating with other breakfast readings, or two-hour readings after comparable meals.

For many non-pregnant adults with diabetes, a commonly used target is about 4–7 mmol/L before meals and below 10 mmol/L two hours after starting a meal. These are broad guideposts, not a personal prescription. Older adults, children, people at risk of hypoglycaemia and those with other medical conditions may have different targets.

Bedtime readings can help identify overnight risk, but they should not be interpreted in isolation. A high bedtime result may follow a late meal, while a low or falling reading may be more concerning in someone using insulin. Ask your healthcare professional which testing times are most useful for your treatment.

Recognising patterns in the numbers

Look for repeated rises or falls rather than reacting to one result. If glucose is regularly high before breakfast, possible contributors include insufficient overnight medication, a late meal, illness or the dawn phenomenon, in which hormones raise glucose in the early morning. A pattern of high readings after a particular meal may point to its carbohydrate amount, portion size or timing.

A log can also reveal delayed effects. A large takeaway meal may produce a modest result at one hour and a much higher result at two or three hours. A brisk walk after dinner may lower the later reading. Poor sleep, emotional stress, infection and steroid medicines can raise glucose even when meals have not changed.

Use simple comparisons. Check whether readings are higher on days with no activity, whether breakfast causes a larger rise than lunch, or whether a medicine appears to affect results at the expected time. Marking these observations in the margin is often more helpful than writing down numbers without context.

When sharing the record, provide at least several days if possible. A GP or diabetes educator may be able to identify a trend from a week of consistent entries, while a shorter record can still help during an illness or medication change. Never alter insulin or other prescribed medicine solely because a graph looks different for one day.

Understanding high and low blood sugar

A high glucose reading is called hyperglycaemia. It may cause thirst, frequent urination, tiredness, blurred vision or headache, although some people feel no symptoms. Repeated high results deserve medical review because prolonged hyperglycaemia can damage blood vessels and nerves over time.

A low reading, or hypoglycaemia, is generally below 4.0 mmol/L in a person treated with insulin or certain diabetes medicines. Symptoms can include trembling, sweating, hunger, dizziness, irritability, confusion and a racing heart. Follow your personal hypo plan; a common approach is to take fast-acting carbohydrate, recheck after about 10–15 minutes and repeat if the level remains low.

Severe confusion, a seizure, collapse or inability to swallow is an emergency. Do not give food or drink to an unconscious person. Call Triple Zero (000) and use prescribed glucagon if an appropriately trained person has it available. A low result without symptoms can still be important, particularly if it happens overnight or repeatedly.

Very high glucose with vomiting, abdominal pain, deep or rapid breathing, severe weakness or drowsiness needs urgent attention. These symptoms can signal diabetic ketoacidosis, especially in type 1 diabetes, and should not be managed by waiting for the next routine appointment. In Australia, healthdirect is available on 1800 022 222 for health advice, while emergencies require 000.

Food, exercise and everyday influences

Carbohydrate-containing foods have the largest direct effect on blood glucose, but the amount, type and combination matter. A bowl of cereal, toast or fruit may raise glucose differently depending on portion size, fibre, protein and what else is eaten. Recording the meal in ordinary terms, such as “two slices of toast with eggs”, is more useful than simply writing “breakfast”.

A balanced pattern of vegetables, legumes, wholegrains, lean protein and unsaturated fats can support steadier levels. Fruit can fit into a diabetes-friendly eating plan, although juice is easier to overconsume and contains less fibre. For a broader look at a fruit often discussed for its antioxidant content, read this guide to the health benefits of pomegranates, while remembering that no single food controls blood sugar.

Movement often lowers glucose by helping muscles use it for energy. A short walk after a meal may make a measurable difference, but strenuous or prolonged exercise can sometimes cause glucose to rise temporarily or fall later. Note the type, duration and timing of activity in the log rather than assuming every workout will have the same effect.

Australian conditions can influence routines. A hot summer day in Perth, a bushwalk near Canberra or a long shift in a warehouse may alter hydration, appetite and glucose readings. Alcohol can also increase the risk of delayed hypoglycaemia, particularly when combined with insulin or certain tablets, so record what and when you drank.

Making the log useful at appointments

Before an appointment, look for three things: readings that are consistently outside your target, unexpected lows, and changes linked with meals or medication. Circle the clearest examples instead of bringing pages of unmarked data. A graph can show the overall direction, while written notes explain why a particular day was different.

Bring the meter, sensor reports and medication list if possible. Meters can have technique-related errors caused by unwashed hands, expired strips, insufficient blood or exposure to heat and humidity. Wash and dry your hands before testing, check strip storage instructions and avoid testing through food residue, which can produce an unexpectedly high result.

Ask your healthcare professional to clarify your personal targets, the best times to test and what action to take at particular readings. The National Diabetes Services Scheme (NDSS) provides support and subsidised products for eligible Australians, and local pharmacies may help with meter technique or supplies. A credentialled diabetes educator can also teach carbohydrate awareness and hypo management.

Pregnancy requires separate targets and closer monitoring. Glucose goals for gestational diabetes are often stricter than general adult targets, and the relevant timing may include fasting and one- or two-hour post-meal readings. Follow the plan from your maternity team rather than applying standard adult ranges to pregnancy.

When a result needs medical review

Arrange a GP appointment if home readings are repeatedly above your target, fasting levels are rising, or symptoms of high glucose continue. A clinician may request a laboratory fasting glucose test, HbA1c, an oral glucose tolerance test or other investigations. HbA1c estimates average glucose over roughly two to three months, while a log shows the day-to-day highs and lows that an average can hide.

Seek prompt advice for repeated readings below 4.0 mmol/L, especially if you do not take diabetes medicine, or if lows occur during driving, exercise or sleep. People who drive for work or travel long distances across Australia should understand the rules and safety steps for checking glucose and managing a hypo before driving.

A meter cannot diagnose diabetes, and a normal-looking log does not rule out every problem. Glucose may fluctuate during infection, after surgery, with hormonal changes or when medicines such as corticosteroids are started. Keep the record factual, include symptoms and take it to a qualified healthcare professional who can interpret the whole clinical picture.