The FBS medical abbreviation means fasting blood sugar, a measure of glucose in the blood after at least 8 hours without food or caloric drinks. Clinicians rely on it to screen for and track diabetes and prediabetes.
Some reports label it FPG for fasting plasma glucose, or simply fasting glucose. It shows up on lab requisitions, wellness visit notes and diabetes follow-up. This page covers what the test shows, the usual cutoffs, how it compares with other sugar tests, and a similar-looking abbreviation, FBSS, which means something else entirely.
At a glance
Stands for
Fasting blood sugar (fasting blood glucose)Written as
FBS, FBG, FPG, fasting glucosePreparation
No food or caloric drinks for at least 8 hoursNormal range
Usually under 100 mg/dL; labs set their own rangeUsed in
Primary care, endocrinology, prenatal care, hospitalDo not confuse with
FBSS, failed back surgery syndrome
What the FBS medical abbreviation tells your clinician
After an overnight fast, the body relies on insulin and the liver to keep blood sugar steady. If glucose stays high even without food, it can mean the body is not making enough insulin or is not responding to it well. That is the basic idea behind diabetes mellitus.
Most fasting tests are drawn first thing in the morning. Water is usually allowed, and many labs ask people to hold off on coffee, juice and gum until after the draw.
Typical cutoffs
| Fasting result | Usual label |
|---|---|
| Under 100 mg/dL | Normal range |
| 100 to 125 mg/dL | Prediabetes, sometimes called impaired fasting glucose |
| 126 mg/dL or higher on two tests | Consistent with diabetes |
Outside the US, many labs report in mmol/L, where the matching cutoffs are about 5.6 and 7.0. Ranges in pregnancy are lower and are set by prenatal guidelines. A single high value is usually repeated or confirmed with another test before a diagnosis.
How an FBS result reads in a note
Primary care note: "FBS 132 mg/dL, repeat 128. A1c ordered. Discussed lifestyle, follow up after results." Two fasting values above the diabetes cutoff, with a second test ordered to confirm the picture before decisions are made.
In hospital, you may also see FSBS, a fingerstick blood sugar taken with a meter at the bedside, often before meals and at bedtime. That is a quick point-of-care check, while FBS usually means a lab draw from a vein.
FBS compared with other sugar tests
| Test | What it measures | Fasting needed |
|---|---|---|
| FBS or FPG | Glucose at one moment after a fast | Yes |
| A1c | Average glucose over about three months | No |
| OGTT | Glucose before and after a sugary drink | Yes |
| Random glucose | Glucose at any time of day | No |
| CGM | Glucose readings around the clock from a skin sensor | No |
Fasting glucose is also part of a BMP or CMP when those are drawn fasting.
FBSS and other look-alikes
The FBSS medical abbreviation means failed back surgery syndrome, ongoing back or leg pain after spine surgery. It appears in pain clinic and spine notes, not lab reports. The extra S is the clue. In research labs, FBS can also mean fetal bovine serum, a cell culture ingredient that has nothing to do with patient testing.
For more shorthand on glucose and related labs, the lab test abbreviations page groups them by type.
Questions before and after the test
- How long is the fast, and are my usual morning pills allowed?
- Is the test a lab draw or a fingerstick?
- Will my result be confirmed with an A1c or a repeat test?
- What range does this lab use?
A fasting glucose number is only one part of the picture. Your doctor or diabetes educator can put your number in context and suggest next steps if any are needed.
Frequently asked questions
What is FBS on my lab slip?
It is fasting blood sugar, the level of glucose in the blood after at least 8 hours without food. Some reports call it fasting plasma glucose or FPG.
Can I drink water before an FBS test?
Plain water is usually allowed and can make the blood draw easier. Avoid food, juice, sweetened drinks and gum unless the lab gives other instructions.
What does FBSS mean?
FBSS means failed back surgery syndrome, ongoing pain after spine surgery. It is unrelated to fasting blood sugar and appears in spine and pain care notes.
Is FBS the same as A1c?
No. FBS shows glucose at a single moment after fasting, while A1c mirrors the typical glucose level across the past few months. The two are often used together.