Understanding tests
HbA1c vs fasting blood sugar: what is the difference?
Understand what HbA1c and fasting blood glucose measure, why preparation differs and how to match your booking to your prescription.
By ApnaPatho • Updated · 2 min read
Two measurements, different questions
Fasting blood glucose measures the glucose in your blood after a specified fast. It gives your clinician a measurement from that collection time.
HbA1c measures glucose attached to haemoglobin and reflects average blood glucose over roughly the previous two to three months. It is used in diabetes assessment and longer-term monitoring when appropriate.
Sources: MedlinePlus: Blood glucose test · MedlinePlus: HbA1c test
Compare the appointment requirements
The names are often grouped together as “sugar tests”, but the preparation and meaning of the results differ.
| Question | Fasting blood sugar | HbA1c |
|---|---|---|
| What does it show? | Blood glucose at the time of collection | Average glucose over roughly 2–3 months |
| Fasting? | Yes; confirm the required interval | Usually not for HbA1c alone |
| Same result units? | Often reported in mg/dL | Usually reported as a percentage or mmol/mol |
Sources: MedlinePlus: Blood glucose test · MedlinePlus: HbA1c test
Why might a clinician request both?
The two tests describe different time periods. A clinician may use more than one measurement to assess the overall picture, investigate a difference between results or monitor care. Some conditions affecting red blood cells can make HbA1c less reliable.
Do not compare the raw numbers as though they use the same scale, or change treatment based on an online table. Bring the complete reports and your medical history to the clinician interpreting them.
Sources: MedlinePlus: Blood glucose test · MedlinePlus: HbA1c test
Match the booking to the prescription
If your prescription says FBS, select fasting blood sugar. If it says HbA1c, select the glycated haemoglobin test. RBS and PPBS are separate listings, not alternate names for HbA1c.
On ApnaPatho, you can place the requested tests in one cart and compare labs that offer the full selection. Before adding a diabetes package as well, check its test list to avoid paying for a duplicate. Choose the collection slot only after confirming preparation for all selected tests.
If the prescription is unclear, ask the prescribing clinic or use prescription upload for help identifying the listed tests. The choice of which measurements you need remains a clinical decision.