Diabetes screening: how FBS and HbA1c differ

What FBS measures

FBS (fasting blood sugar) measures glucose after at least eight hours without food. It reflects that moment, so it is sensitive to fasting, sleep, stress and acute illness.

It is easy to perform and inexpensive, which is why it appears in almost every health package. Its limits are the fasting requirement and the fact that it says nothing about long-term average glucose.

What HbA1c measures

HbA1c measures the proportion of haemoglobin that has become glycated over the roughly 2-3 month lifespan of red blood cells. It therefore reflects average glucose and needs no fasting.

Its limitations include anaemia, thalassaemia, recent transfusion and some stages of kidney disease, where values can be misleading, so doctors interpret it individually.

Who should start screening

Screening is generally recommended from age 35, and earlier for people with risk factors.

• Overweight or with a larger waist, especially alongside high blood pressure
• Family history of diabetes
• Previous gestational diabetes during pregnancy
• Glucose found in urine, or abnormal blood pressure and lipid values
• Long-term use of medicines that affect glucose, such as steroids

How to read an initial result

A single value above the reference range does not automatically mean diabetes. Doctors usually confirm with a repeat test or a different testing method.

If you have pre-diabetes, dietary changes and more physical activity genuinely slow progression to diabetes, so regular follow-up matters.