Normal blood sugar levels: fasting, after meals and the OGTT

“Is my sugar normal?” is one of the most common questions in any clinic. The answer depends on when the blood was taken (fasting, after food, or at random), how it was measured (a lab sample or a finger-prick meter), and who you are (someone without diabetes, someone with diabetes, or a pregnant woman). This page covers adults who are not pregnant. All values are in mg/dL, the unit Indian labs use. If your report or meter shows mmol/L, use the blood sugar unit converter.

What is a normal fasting sugar?

A fasting sugar is taken after at least eight hours without food or sugary drinks, usually first thing in the morning. Water is fine. For a lab test on venous plasma:

• Below 100 mg/dL: normal
• 100 to 125 mg/dL: impaired fasting glucose, a form of prediabetes
• 126 mg/dL or more: in the diabetes range

A single high value is usually repeated, or checked with another test such as HbA1c, before a diagnosis is made. The exception is a clearly high sugar with typical symptoms.

What is a normal sugar after meals?

Many Indian labs offer a “PP” or post-prandial sugar, taken two hours after a usual meal. There is no single official cut-off for this test, because meals differ so much. In people without diabetes, the sugar usually rises after food and comes back below about 140 mg/dL within two hours. A PP sugar of 200 mg/dL or more is a strong signal to get formally tested.

The standardised version of this test is the oral glucose tolerance test (OGTT), described below. A PP sugar after a home meal is useful for monitoring, but the OGTT is the test used for diagnosis.

What about a random sugar?

A random sugar is taken at any time, regardless of meals. In adults, a random sugar of 200 mg/dL or more, together with classic symptoms such as heavy thirst, passing a lot of urine or unexplained weight loss, is enough to diagnose diabetes. A lower random value does not rule diabetes out.

What is the OGTT and what do the results mean?

In the oral glucose tolerance test, you come fasting, a blood sample is taken, and you drink a measured glucose solution given by the lab. Blood is taken again after two hours. You sit quietly during the test and avoid food, tea or walking around. The two-hour value is read as:

• Below 140 mg/dL: normal
• 140 to 199 mg/dL: impaired glucose tolerance, a form of prediabetes
• 200 mg/dL or more: in the diabetes range

The OGTT picks up some people whose fasting sugar is still normal. This is common in South Asians, whose sugar often rises after food before the fasting value changes. The International Diabetes Federation has also proposed using a one-hour value in the OGTT to catch risk earlier. This is not yet used everywhere, so your lab may report only the fasting and two-hour values.

Pregnancy uses a different OGTT and lower cut-offs. Read what causes gestational diabetes.

How does HbA1c fit in?

HbA1c reflects your average sugar over about three months and does not need fasting. Below 5.7% is usually normal, 5.7% to 6.4% is prediabetes and 6.5% or more is diabetes. Read what your HbA1c result means. If you have prediabetes on any test, read what prediabetes means.

Why might my results not agree?

It is quite common for one test to be in the prediabetes range and another to be normal. Each test looks at a different side of sugar control. Your doctor will usually repeat the test that was abnormal, or use a second type of test, and decide based on the whole picture.

Readings can also differ between a lab test and a home meter, and between labs, because of sample type, timing and how long the sample waited before testing. Read why glucometer and lab readings differ.

What targets apply if I already have diabetes?

Targets for people with diabetes are not the same as “normal” values. Many adults with diabetes are advised to aim for a fasting or pre-meal sugar of about 80 to 130 mg/dL and an after-meal peak below 180 mg/dL, but this is individual. Older adults and people prone to low sugar often have more relaxed targets, and pregnancy uses tighter ones. Your doctor will set targets that are safe for you.

When is a low sugar a concern?

A sugar below 70 mg/dL is considered low. It is most often seen in people on insulin or some tablets for diabetes. Low sugars in someone not on diabetes medicines are unusual and need to be checked by a doctor.

What should I ask my doctor?

• Was my sample a fasting, after-meal or random test, and was it a lab or meter reading?
• Do I need a repeat test, an OGTT or an HbA1c to confirm the result?
• If I have diabetes, what are my personal fasting and after-meal targets?

If your sugar is in the prediabetes or diabetes range, or the results confuse you, book a consultation.