FBS, PPBS, HbA1c or OGTT? Which Diabetes Test You Need and What the Numbers Mean

Quick answer: For screening, most doctors use HbA1c (your three-month average) plus Fasting Blood Sugar (FBS). Post-Prandial Blood Sugar (PPBS) — taken two hours after a meal — shows how well your body handles food and is useful for people already diagnosed. The Oral Glucose Tolerance Test (OGTT) is the most sensitive test and is used in pregnancy and when other results are borderline. Diabetes is suggested by FBS ≥126 mg/dL, HbA1c ≥6.5%, OGTT 2-hour value ≥200 mg/dL, or a random sugar ≥200 mg/dL with symptoms.

World Diabetes Day is on 14 November. India has one of the largest numbers of people with diabetes in the world, and a very large number of adults have pre-diabetes without knowing it. The good news: diagnosis needs only simple, inexpensive blood tests. The confusing part is that there are five of them.

The Five Common Blood Sugar Tests

1. Fasting Blood Sugar (FBS)

• What it measures: your blood glucose after 8–12 hours without food
• Why it matters: shows how your body controls sugar overnight, when no food is coming in
• Preparation: no food or drinks except water for 8–12 hours

2. Post-Prandial Blood Sugar (PPBS)

• What it measures: blood glucose exactly two hours after starting a normal meal
• Why it matters: shows how your body handles a meal — often the first number to rise
• Preparation: eat your usual breakfast or lunch, note the time you start eating, and give the sample two hours later. Don't walk extra or skip half the meal "to get a better result"

3. Random Blood Sugar (RBS)

• What it measures: glucose at any time of day, regardless of meals
• Why it matters: quick check in someone with symptoms like extreme thirst, frequent urination or weight loss
• Limitation: not used alone to rule diabetes out

4. HbA1c (Glycated Haemoglobin)

• What it measures: the percentage of haemoglobin with glucose attached — an average of the previous two to three months
• Why it matters: not affected by what you ate last night; the best single test for long-term control
• Preparation: no fasting needed
• Limitation: can be misleading in anaemia, some haemoglobin disorders (such as thalassaemia trait), recent blood loss or transfusion, and pregnancy

Read our in-depth guide to HbA1c.

5. Oral Glucose Tolerance Test (OGTT)

• What it measures: fasting glucose, then glucose two hours after drinking a standard 75 g glucose solution
• Why it matters: the most sensitive way to detect early diabetes and gestational diabetes
• Preparation: fast for 8–12 hours; plan to sit at the lab for about two and a half hours without eating, smoking or walking around

What Do the Numbers Mean?

Fasting Blood Sugar

• Normal: below 100 mg/dL
• Pre-diabetes (impaired fasting glucose): 100–125 mg/dL
• Diabetes: 126 mg/dL or higher (confirmed on a repeat test)

HbA1c

• Normal: below 5.7%
• Pre-diabetes: 5.7%–6.4%
• Diabetes: 6.5% or higher

OGTT — 2-Hour Value

• Normal: below 140 mg/dL
• Pre-diabetes (impaired glucose tolerance): 140–199 mg/dL
• Diabetes: 200 mg/dL or higher

Post-Prandial Sugar (Two Hours After a Meal)

For people without diabetes, post-meal sugar generally stays below 140 mg/dL. Many doctors aim for below 180 mg/dL in people being treated for diabetes, though individual targets vary.

Random Blood Sugar

A random value of 200 mg/dL or higher with classic symptoms suggests diabetes.

These are internationally used diagnostic thresholds. A diagnosis should be made by your doctor, usually after a confirmatory repeat test unless symptoms are obvious.

Which Test Should You Take?

• First-time screening, adult over 30 or with risk factors: HbA1c + FBS. Both are included in Aarvak's ₹1,000 ADC Basic Swasthya Panel.
• Already diabetic, monitoring control: HbA1c every three months until stable, then every three to six months; FBS and PPBS as advised; home glucometer readings in between.
• Pregnant: OGTT as advised by your obstetrician, usually between 24 and 28 weeks, or earlier if you are at high risk. See our pregnancy tests guide.
• Borderline results (FBS 100–125 or HbA1c 5.7–6.4%): your doctor may order an OGTT to clarify. Read our pre-diabetes guide.
• Symptoms now (extreme thirst, urination, weight loss, blurred vision): random sugar plus HbA1c — and see a doctor the same day.

Who Should Be Screened?

• Everyone over 30–35, even without symptoms
• People who are overweight, especially with a large waist
• Anyone with a parent or sibling with diabetes
• Women who had gestational diabetes or have PCOS (see our PCOS hormone testing guide)
• People with high blood pressure or high triglycerides
• Anyone with a sedentary job and little exercise

Additional Tests Once You're Diagnosed

• Kidney Function Test and urine microalbumin every year
• Lipid profile every year
• Vitamin B12 if on metformin for a long time
• Liver function test — fatty liver often goes with diabetes. See fatty liver disease

Frequently Asked Questions

What is the best test to diagnose diabetes?

HbA1c and fasting blood sugar are the most commonly used screening tests. The OGTT is the most sensitive and is preferred in pregnancy or when other results are borderline.

What is a normal HbA1c level?

An HbA1c below 5.7% is normal. 5.7% to 6.4% indicates pre-diabetes, and 6.5% or higher indicates diabetes.

What is the difference between PPBS and OGTT?

PPBS measures blood sugar two hours after your normal meal. OGTT measures it two hours after a standard 75 g glucose drink, which makes the result more standardised and comparable.

Do I need to fast for an HbA1c test?

No. HbA1c does not require fasting. Fasting is needed only if a fasting sugar or lipid profile is being done at the same time.

Can HbA1c be wrong?

HbA1c can be falsely high or low in anaemia, thalassaemia trait and other haemoglobin variants, after blood loss or transfusion, and in pregnancy. Your doctor may use fasting sugar or OGTT instead in these situations.

How often should a diabetic test HbA1c?

Usually every three months while treatment is being adjusted, and every three to six months once sugars are stable, as advised by the doctor.

Book Diabetes Screening in Gurugram

This World Diabetes Day, know your numbers. Aarvak performs FBS, PPBS, HbA1c and OGTT at our Sector 67 lab, with home sample collection for fasting and HbA1c tests. Reports are usually ready within 6–8 hours. Call +91 92663 33711 or book online.

This article is for general information only. Diagnosis and treatment of diabetes should be done by a qualified doctor.