Why has my blood sugar or HbA1c gone up?

Why has my blood sugar or HbA1c gone up?

Explore why blood sugar or HbA1c may rise, from everyday changes and medicines to patterns across health screenings.

· 5 min read

Blood sugar or HbA1c can rise for everyday reasons such as a stretch of less activity, weight gain, an illness, stress or a new medicine. Over several years, the body can also slowly make less insulin, so blood sugar drifts up on its own.

A single higher reading is not always a real change. Both measurements move a little between tests. What matters is the pattern across several results, whether anything else in your life has changed, and whether the reading has crossed Singapore's thresholds for prediabetes or diabetes.

What can cause blood sugar to rise?

The causes can be short-term or long-term.

Short-term rises are usually from day-to-day changes and are normal. Blood sugar climbs after any meal, especially one high in sugar or refined carbohydrates. Eating more or moving less than usual, drinking alcohol, or an illness can also push it up for a few days. These usually settle on their own once things return to normal.

Long-term rises are the ones to watch. Over months and years, poor diet, inactivity and weight gain make the body's cells less responsive to insulin, the hormone that moves sugar into your cells. The pancreas compensates by producing more insulin, often for years, until it begins to fall behind and blood sugar starts to drift up. If your results have crept up test by test, take that pattern seriously even if each one looked only slightly high.

Can medications, illness or stress raise blood sugar?

Yes. Stress, illness and some medicines can all raise blood sugar, sometimes for only days or weeks.

When you are stressed, your body releases adrenaline and cortisol, hormones that push blood sugar up. An illness such as a cold or flu puts the body under similar strain.

Steroids (glucocorticoids), often prescribed for asthma, allergies or joint problems, are the best-known medicines that raise blood sugar. In one large analysis, about a third of people without diabetes who took them developed high blood sugar. Some antipsychotics, statins, beta blockers, diuretics and hormone treatments are also linked to higher blood sugar. The rise is sometimes temporary and settles once the course of medicine is finished.

If you think a medicine may explain a change in your results, raise it with the doctor who prescribed it.

Why is my blood sugar high in the morning?

In the early hours, the body releases hormones that push blood sugar up. In healthy people, extra insulin keeps the morning reading normal. In diabetes, that compensation is weaker and the number rises — a pattern called the dawn phenomenon.

If you do not have diabetes and a fasting test came back high, check the basics first: fasting needs at least 8 hours with nothing but water, and a recent illness or stress can also push the number up. In Singapore, a fasting result of 7.0 mmol/L or higher is in the diabetes range, so if yours is in or near it, a repeat test is the usual next step. The full blood sugar chart shows the other ranges.

Does HbA1c fluctuate, and how big a change matters?

Yes. HbA1c moves a little between tests even when nothing in your life has changed. A 2023 review found that it varies naturally within the same person, much less in people without diabetes than in people with diabetes. For someone with diabetes, a change of about 1 percentage point can still fall within this normal swing. Iron deficiency and thalassaemia (an inherited blood disorder) can also make a result less reliable, as the HbA1c guide explains.

Against that noise, a rise carries more weight when it shows up on two or more tests in a row, when it crosses 7%, or, if you have diabetes, when it moves away from your agreed target (7.0% or below for most people with type 2 diabetes).

What other health markers should I look at alongside blood sugar?

Blood sugar does not sit on its own. Doctors look at a few markers together — blood sugar, blood pressure, cholesterol and weight — because they move with each other, and a change in one often shows up in the others.

Excess fat around internal organs makes the body less responsive to insulin, which in turn tends to raise blood pressure and shift cholesterol in an unhealthy direction. For Asians, diabetes risk rises from a body mass index (BMI) of 23, so a few kilos gained since your last check-up can help explain a higher reading. If you have diabetes, Singapore's care targets cover HbA1c, blood pressure and cholesterol together — the three markers that signal metabolic health. For more on this, see how blood pressure, cholesterol and blood sugar fit together.

When you add your past and recent health screening reports to the Health Locker in the Genie Health app, Genie reads values like blood sugar, HbA1c, blood pressure and cholesterol from each report and organises them into Health Pillars, so you see each area in one view. Genie then analyses and connects related markers across your reports, surfacing insights as Sparks cards — for example, flagging that your HbA1c and LDL cholesterol have both drifted up over the last two screenings. You can also ask Genie to pull your markers side by side over time and take a complete picture to your next doctor's appointment.

FAQs

What can cause blood sugar to rise?
The causes can be short-term or long-term.
Can medications, illness or stress raise blood sugar?
Yes. Stress, illness and some medicines can all raise blood sugar, sometimes for only days or weeks.
Why is my blood sugar high in the morning?
In the early hours, the body releases hormones that push blood sugar up. In healthy people, extra insulin keeps the morning reading normal. In diabetes, that compensation is weaker and the number rises — a pattern called the dawn phenomenon.
Does HbA1c fluctuate, and how big a change matters?
Yes. HbA1c moves a little between tests even when nothing in your life has changed. A 2023 review found that it varies naturally within the same person, much less in people without diabetes than in people with diabetes. For someone with diabetes, a change of about 1 percentage point can still fall within this normal swing. Iron deficiency and thalassaemia (an inherited blood disorder) can also make a result less reliable, as the HbA1c guide explains.
What other health markers should I look at alongside blood sugar?
Blood sugar does not sit on its own. Doctors look at a few markers together — blood sugar, blood pressure, cholesterol and weight — because they move with each other, and a change in one often shows up in the others.

References & Sources

  1. Hyperglycemia (High Blood Glucose) https://diabetes.org/living-with-diabetes/treatment-care/hyperglycemia
  2. How diabetes develops https://www.healthhub.sg/programmes/diabetes-hub/how-diabetes-develops
  3. Diabetes and stress https://www.healthhub.sg/programmes/diabetes-hub/diabetes-and-stress
  4. Medication-Induced Hyperglycemia and Diabetes Mellitus: A Review of Current Literature and Practical Management Strategies https://pmc.ncbi.nlm.nih.gov/articles/PMC11330434/
  5. Within-subject variation of HbA1c: A systematic review and meta-analysis https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0289085
  6. Treatment targets and monitoring https://www.healthhub.sg/programmes/diabetes-hub/treatment-targets-and-monitoring

Note: This content is for general informational purposes only and is not medical advice, diagnosis or treatment. It does not replace consultation with a qualified healthcare professional. If you have concerns about your health, please consult a qualified physician.

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