You test your blood sugar first thing in the morning. The number looks fine, and you put the meter away feeling reassured. If you also take your steroids in the morning, that reassurance may be misleading.
Roughly one in three people taking steroids develop higher blood sugar, and around one in five develop what is often called steroid diabetes. Most of that rise happens in the afternoon and evening, hours after you swallowed the tablet, and it has usually settled again by the time you wake up the next day.
Why the afternoon is the part that matters
A morning dose of prednisone tends to raise your blood sugar about 4 to 8 hours later. It climbs through the afternoon, holds into the evening, and drifts back down overnight.
This is why a morning reading can look perfectly normal while your levels run high every afternoon. The HbA1c blood test your doctor orders may have the same blind spot, because it averages roughly three months and smooths out those peaks in blood sugar.
If you take prednisone or dexamethasone, or split your dose across the day, your pattern will be flatter and more constant. It is worth asking which applies to you.
These effects can be worrying and often leave patients wishing they had more information up front. Stephanie Williams, BS, RRT, Project Lead, Speak Up for COPD
When to check
If you already have diabetes, you will probably need to test more often than usual while you are on steroids. If you do not have diabetes, but your age, family history, a previous prediabetes result, or a higher steroid dose puts you at greater risk, this is still worth raising with your doctor.
For test timing, aim for before lunch, or one to two hours after lunch or your evening meal. That is the window where the steroid effect shows itself if you are taking your steroid dose in the morning.
Two small things make readings more reliable. Wash and dry your hands first, because traces of fruit juice or hand lotion can push a reading up. And use your fingertip rather than your forearm, which lags behind when glucose is changing quickly.
Making sense of what you see
A fasting reading below 100 mg/dL is considered normal, and after meals most guidance aims for under 180 mg/dL. An afternoon number higher than you are used to is not a sign you have done something wrong. It is the medication doing what it does.
Alongside the numbers, notice how you feel. Increased thirst, needing to urinate more often, tiredness and blurred vision are all worth mentioning.
There is one moment that catches people out. As your steroid dose comes down, your blood sugar usually comes down with it. If you take insulin or diabetes tablets, those may need to be reduced at the same time, or your levels can drop too low. Have that conversation with your doctor before your taper begins rather than partway through it.
Keeping a record worth sharing
A log is more useful than a memory, and it does not need to be complicated. Note the reading, the time, when you took your steroid, roughly what you ate and how you felt. That is enough for your doctor to spot a pattern.
A paper notebook works perfectly well. If you prefer an app, mySugr and Glooko both connect to common meters and produce a summary you can hand over at an appointment.
You may also have come across continuous glucose monitors, small sensors worn on the arm that track levels around the clock. They catch the afternoon rise that finger checks miss. In the US, Medicare and most insurers cover them for people using insulin, and since 2024, sensors have been sold over the counter, though these are not designed for insulin users.
When to call your care team
Ask this question early, ideally when your monitoring starts: "What number should make me call you?"
Their answer, written down somewhere you can find it, turns an alarming reading into a clear next step. Get in touch sooner if your readings sit above what you agreed, or if the thirst and tiredness are getting worse. If you feel truly unwell, with vomiting, stomach pain, labored breathing or confusion, treat that as urgent and seek help straight away.
You are not being a nuisance by checking. You are giving your care team the insight they cannot get from a single blood test in a clinic room.