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The rise may be particularly relevant during more significant infections or periods of physical stress. However, an isolated high reading does not necessarily mean a person has developed diabetes. Understanding why this happens, how long blood sugar can remain elevated, and when it warrants further testing can help people interpret glucose changes during illness.

Why can infections raise blood sugar?

Dr Palleti Siva Karthik Reddy, MBBS, MD, General Medicine, FAIG, Consultant Physician at Elite Care Clinic, tells indianexpress.com, “Infection puts the body into a physiological stress state. Hormones such as cortisol, adrenaline and glucagon rise to help the body meet the increased energy demands of fighting the infection. These hormones stimulate the liver to release more glucose into the bloodstream while simultaneously making tissues less sensitive to insulin. As a result, glucose uptake by muscles and other tissues falls, even though the pancreas may be producing insulin normally. This is known as stress hyperglycaemia and can occur temporarily even in people who have never been diagnosed with diabetes.”

How high can blood sugar rise during an infection?

There is no single blood glucose level that defines infection-related hyperglycaemia because the rise depends on the severity of the infection, medications being used, and an individual’s underlying metabolic health. Mild elevations can occur with relatively minor illness, while severe infections can produce much higher readings.

“The important point is that a single high glucose reading during an acute infection cannot by itself establish diabetes. Once the person has recovered, fasting glucose and HbA1c can help determine whether the elevation was temporary or reflects an underlying problem. HbA1c is particularly useful because it reflects average blood glucose over roughly the previous two to three months and is less affected by a short episode of illness,” notes Dr Reddy.

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When should blood sugar be retested after an infection?

Quick Quiz

See if you can answer this:

When should blood sugar be checked again after recovering from an infection?

A. Never, because elevated glucose during an infection is always temporary.

B. Only if the person develops a fever again.

C. If glucose remains elevated after recovery, particularly with repeated high readings, a follow-up fasting glucose and HbA1c can help establish the baseline.

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D. Immediately after every infection, regardless of symptoms or glucose levels.

Reveal the answer

✅ Correct answer: C

Dr Reddy shares that blood sugar often begins to return towards normal as an infection and the body’s stress response settle, but the timeline varies. Persistently elevated glucose after recovery should not automatically be blamed on the infection. Repeatedly high fasting or random readings should be discussed with a doctor, and follow-up fasting glucose and HbA1c testing can help establish the person’s baseline. Symptoms such as excessive thirst, frequent urination, unexplained weight loss or marked fatigue warrant prompt medical evaluation.