Empeiria

Glucose

Also known as blood sugar, blood glucose, fasting glucose, FBG

C₆H₁₂O₆ small molecule

LOINC 2345-7 code verified serum mg/dL

unverified These explanations are written to be easy to read and have not yet been checked against a source. The ranges and measurement notes on this page show theirs.

definition unverified

The amount of sugar circulating in your blood right now. It is the main fuel your cells run on.

The amount of sugar circulating in your blood right now. It is the main fuel your cells run on.

No clinical version written yet.

why measured unverified

It screens for diabetes and for the insulin resistance that precedes it.

It screens for diabetes and for the insulin resistance that precedes it.

No clinical version written yet.

if high unverified

Your body is having trouble moving sugar out of the blood. A single high reading is not a diagnosis, particularly if you were not fasting.

Your body is having trouble moving sugar out of the blood. A single high reading is not a diagnosis, particularly if you were not fasting.

No clinical version written yet.

if low unverified

This is not common unless you take diabetes medicine. A truly low reading with symptoms should be looked into.

This is not common unless you take diabetes medicine. A truly low reading with symptoms should be looked into.

No clinical version written yet.

caveats unverified

Only a fasting result is really interpretable, and fasting means no food for eight hours. A result taken after eating has a much wider normal range, and comparing the two is meaningless.

Only a fasting result is really interpretable, and fasting means no food for eight hours. A result taken after eating has a much wider normal range, and comparing the two is meaningless.

No clinical version written yet.

What this substance is

formula
C₆H₁₂O₆
mass
180.156 g/mol
monoisotopic
180.06339
charge
0
InChIKey
WQZGKKKJIJFFOK-GASJEMHNSA-N
ChEBI
CHEBI:4167
CAS
50-99-7

Drawn from ChEBI's own curated 2D drawing, accepted only after its InChIKey, formula and charge matched the ChEBI release. Nothing here is hand-entered. Two masses are given because they answer different questions: the average is natural-abundance weighted and drives unit conversion; the monoisotopic value uses only the commonest isotope of each element and is what mass spectrometry measures.

3D model · Glucose

The 3D model shows beta-D-glucose, the majority form. In blood, glucose flips between beta and alpha forms, which differ only in the orientation of one OH group. Generated by RDKit from ChEBI's verified structure, and accepted only because its own 3D geometry reproduces ChEBI's InChIKey. A flexible molecule takes many shapes; this is one low-energy one. Drag to rotate, scroll to zoom.

Reference ranges

Checking your own result against this range needs the running application; this is a static copy. Nothing you type anywhere in Empeiria is ever sent to a server.

Applies toNormalOptimalCritical
all · fasting ≤ 99 mg/dL — —

guideline limit Diabetes Tests & Diagnosis, NIDDK (National Institutes of Health) cited · not yet checked by a person

How it is measured

In practice

Most lab glucose tests use blood from a vein in your arm. For a fasting test you must not eat or drink anything but water for at least 8 hours. For a glucose tolerance test, blood is taken before and after a sugary drink. People with diabetes can check their glucose at home with a finger-prick meter or a sensor under the skin (CGM).

Venous blood sample by venipuncture. Fasting plasma glucose requires no caloric intake for at least 8 h; random glucose can be drawn at any time. The OGTT uses a 75 g anhydrous glucose load with samples before and after the drink; the gestational glucose challenge needs no fasting and is sampled 1 hour after the drink. Self-monitoring uses capillary fingerstick meters with test strips, and continuous glucose monitors use a subcutaneous sensor that estimates glucose every few minutes.

Before the test

  • For a fasting glucose or oral glucose tolerance test, fast (nothing but water) for at least 8 hours.
  • Ask your provider whether you need to fast before your glucose test.

Where: laboratory, home

Sources: 2. Classification and Diagnosis of Diabetes: Standards of Care in Diabetes-2023, American Diabetes Association, Diabetes Care (PMC open access); Blood Glucose Test, MedlinePlus (U.S. National Library of Medicine) cited · not yet checked by a person

In the lab

enzymatic colorimetric

Hexokinase / glucose-6-phosphate dehydrogenase

Two enzymes are added to the sample. They change the sugar step by step, and the last step makes a substance that absorbs light. The machine measures how much light is absorbed, and that tells it how much sugar there was.

Hexokinase phosphorylates glucose to glucose-6-phosphate, which G6PD then oxidises while reducing NADP+ to NADPH. The rise in absorbance from the NADPH formed reflects the glucose present.

  • Read by: Absorbance at 340 nm
  • Reference method: Isotope-dilution mass spectrometry
  • Standardised to: Calibration standardised against isotope-dilution mass spectrometry (ID/MS)

What can throw it off

  • Glycolysis in the tube: cells keep consuming glucose after the draw, so an unseparated sample reads progressively lower -- on average roughly 5-7% per hour, faster at higher temperature or white-cell count.
  • Severe haemolysis

Plasma should be separated from the cells promptly (within 30-45 minutes in the NHANES protocol). Fluoride tubes slow glycolysis over hours but barely help in the first hour, so they do not replace prompt separation.

Why labs disagree: Plasma holds about 11% more water than whole blood, so with a normal haematocrit plasma glucose reads about 11% higher than whole-blood glucose. Meters can be calibrated to report a plasma-equivalent value from a whole- blood drop, and fingerstick blood can read higher than a vein sample after a glucose load, which is why a fingerstick and a lab draw taken minutes apart can legitimately differ.

Sources: Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus (Diabetes Care 2011; NACB/ADA), PMC open access; NHANES 2017-2018 Laboratory Procedure Manual: Glucose (refrigerated serum), CDC/NCHS cited · not yet checked by a person

What it reports on

Associated symptoms

When high
When low

Conditions this marker features in

When high
  • high A cluster of risks that travel together · defining
    One of the five criteria (three are needed): fasting blood sugar of 100 mg/dL or higher, or taking medicine for high blood sugar. These are criteria for a risk-factor cluster, not a diagnosis of a single disease.
  • high Blood sugar higher than normal, but not diabetes · defining
    ADA criterion: fasting glucose 100–125 mg/dL, or 140–199 mg/dL two hours into a glucose tolerance test.
  • high Type 2 diabetes · defining
    Fasting glucose 126 mg/dL (7.0 mmol/L) or higher; a 2-hour glucose-tolerance value of 200 mg/dL or higher; or a random value of 200 mg/dL or higher with classic symptoms.
  • high High blood sodium · supportive
    High blood glucose changes how sodium should be read, so sodium is corrected for glucose. High glucose can also cause water loss through the urine.
Either direction
  • either High blood potassium · monitoring
    Insulin with glucose is a common emergency treatment, so blood glucose is checked every hour for at least 2 hours afterwards. Both low and high glucose can follow.

Ordered as part of

cmp · bmp · metabolic_risk