Searchable dictionary
Biomarker dictionary
18 markers
Total cholesterol
TCLipids
- What it is
- The total amount of cholesterol carried in your blood, a waxy fat the body needs to build cells and hormones.
- Why it is measured
- It is part of a routine lipid panel used to estimate long-term cardiovascular risk alongside HDL, LDL and triglycerides.
- How to read it
- Total cholesterol on its own says little. What matters is the balance between the fractions (HDL, LDL) and your overall risk picture, which your doctor weighs together.
Usual units
mmol/L (or mg/dL)
Commonly reported
Often reported as desirable below about 5.0 mmol/L, but targets are personal
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHS / AHALDL cholesterol
LDLLipids
- What it is
- Cholesterol carried by low-density lipoprotein particles. Excess LDL can build up in artery walls over time.
- Why it is measured
- It is one of the strongest lipid markers linked to cardiovascular risk, so it guides prevention conversations.
- How to read it
- Lower is generally considered better, but the target depends on your personal risk. People at higher risk are often given a lower target by their doctor.
Usual units
mmol/L (or mg/dL)
Commonly reported
Targets are individual and set with your doctor, not one fixed number
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHS / AHAHDL cholesterol
HDLLipids
- What it is
- Cholesterol carried by high-density lipoprotein, which helps move cholesterol away from the arteries back to the liver.
- Why it is measured
- Higher HDL is generally associated with lower cardiovascular risk, so it balances the LDL picture.
- How to read it
- Unlike LDL, a higher HDL is usually viewed favourably. Very high values are still best interpreted in context by your doctor.
Usual units
mmol/L (or mg/dL)
Commonly reported
Commonly reported as more favourable above roughly 1.0 to 1.2 mmol/L
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHS / AHATriglycerides
TGLipids
- What it is
- The most common type of fat in the body, used for energy and influenced strongly by recent meals.
- Why it is measured
- Raised triglycerides are linked to metabolic and cardiovascular risk, especially with low HDL.
- How to read it
- Because food raises them sharply, triglycerides are usually measured fasting. A single high reading after a meal is often rechecked.
Usual units
mmol/L (or mg/dL)
Commonly reported
Often reported as normal below about 1.7 mmol/L when fasting
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHS / AHAFasting glucose
FBGGlucose
- What it is
- The amount of sugar in your blood after not eating for several hours.
- Why it is measured
- It is a core screen for prediabetes and diabetes and for tracking metabolic health.
- How to read it
- Because it is affected by recent food, it is measured after fasting. Diagnosis is never based on one reading alone; your doctor confirms with repeat or additional tests.
Usual units
mmol/L (or mg/dL)
Commonly reported
Commonly reported normal fasting range around 3.9 to 5.5 mmol/L (labs vary)
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
WHO / ADAHbA1c
A1cGlucose
- What it is
- A measure of average blood sugar over roughly the past two to three months, based on sugar attached to haemoglobin.
- Why it is measured
- It gives a longer-term view of glucose control than a single fasting reading.
- How to read it
- HbA1c smooths out day-to-day swings. Certain conditions affecting red blood cells can distort it, which is why your doctor interprets it in context.
Usual units
mmol/mol (or %)
Commonly reported
Often reported in mmol/mol (SI) or percent; thresholds are set by your clinician
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
WHO / ADACreatinine
creatKidney
- What it is
- A waste product from normal muscle activity that the kidneys filter out of the blood.
- Why it is measured
- Blood creatinine is used to estimate how well the kidneys are filtering.
- How to read it
- It is influenced by muscle mass, hydration and some medicines, so it is read together with eGFR rather than alone.
Usual units
micromol/L (or mg/dL)
Commonly reported
Reference ranges differ by sex, age and lab method
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHS / NICEeGFR
estimated GFRKidney
- What it is
- An estimate of how much blood your kidneys filter each minute, calculated from creatinine, age and sex.
- Why it is measured
- It is the main number used to stage and monitor kidney function over time.
- How to read it
- A single lower value can be temporary (for example with dehydration). Trends over months matter more than one reading, and your doctor interprets the stage.
Usual units
mL/min/1.73m2
Commonly reported
Commonly reported as 90 or above in healthy adults; interpretation is clinical
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NICE / NHSALT
alanine aminotransferaseLiver
- What it is
- An enzyme found mainly in liver cells that leaks into the blood when the liver is irritated.
- Why it is measured
- It is part of a liver function panel used to screen for liver stress or injury.
- How to read it
- Mild elevations are common and often not serious, but they are followed up in context. Exercise and some supplements can raise it briefly.
Usual units
U/L
Commonly reported
Reference ranges vary by lab and sometimes by sex
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHSGGT
gamma glutamyl transferaseLiver
- What it is
- An enzyme linked to the liver and bile ducts.
- Why it is measured
- It helps interpret other liver results and is sensitive to alcohol and certain medicines.
- How to read it
- GGT is read alongside ALT and ALP rather than on its own. A raised value points your doctor to further questions, not a diagnosis.
Usual units
U/L
Commonly reported
Reference ranges vary by lab
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHSTSH
thyroid stimulating hormoneThyroid
- What it is
- A hormone from the pituitary gland that tells the thyroid how much thyroid hormone to make.
- Why it is measured
- It is the first-line screen for an under- or over-active thyroid.
- How to read it
- TSH moves in the opposite direction to thyroid hormone, which can be confusing. It is often paired with free T4, and one borderline value is usually rechecked.
Usual units
mIU/L
Commonly reported
Commonly reported around 0.4 to 4.0 mIU/L (labs and life stage vary)
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHS / NICEFree T4
FT4Thyroid
- What it is
- The active, unbound form of the main thyroid hormone circulating in your blood.
- Why it is measured
- It is measured with TSH to build a fuller picture of thyroid function.
- How to read it
- Free T4 is interpreted next to TSH, not alone. The pattern of the two together is what guides your doctor.
Usual units
pmol/L
Commonly reported
Reference ranges vary by lab and assay
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHS / NICEHaemoglobin
HbBlood count
- What it is
- The protein in red blood cells that carries oxygen around the body.
- Why it is measured
- Low haemoglobin can indicate anaemia; it is a core part of a full blood count.
- How to read it
- Ranges differ by sex and altitude, and a low value has many possible causes. Your doctor looks at the whole blood count and your symptoms.
Usual units
g/L (or g/dL)
Commonly reported
Reference ranges differ by sex and lab
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHSFerritin
iron storesBlood count
- What it is
- A protein that stores iron, so blood ferritin reflects the body iron reserves.
- Why it is measured
- It is used to check for low iron stores or iron overload.
- How to read it
- Ferritin also rises with inflammation, so a normal or high value does not always mean iron stores are fine. It is interpreted with other iron tests.
Usual units
micrograms/L
Commonly reported
Reference ranges differ by sex and lab
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHS / WHOWhite blood cell count
WBCBlood count
- What it is
- The number of infection-fighting cells in a sample of blood.
- Why it is measured
- It helps flag infection, inflammation or other conditions as part of a full blood count.
- How to read it
- It moves up and down for many everyday reasons, including recent illness. A one-off mild change is often rechecked rather than acted on.
Usual units
x10^9/L
Commonly reported
Commonly around 4 to 11 x10^9/L (labs vary)
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHSVitamin D
25-OH vitamin DVitamins
- What it is
- A measure of the storage form of vitamin D, which supports bone and muscle health.
- Why it is measured
- It is checked when a deficiency is suspected, for example with bone or muscle symptoms.
- How to read it
- Sunlight, season and skin all affect it. Thresholds for "low" differ between guidelines, so your doctor decides what your value means for you.
Usual units
nmol/L (or ng/mL)
Commonly reported
Reported in nmol/L or ng/mL; cut-offs differ between guidelines
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHS / NICEVitamin B12
B12Vitamins
- What it is
- A vitamin needed for healthy nerves and red blood cells.
- Why it is measured
- It is checked for tiredness, nerve symptoms or certain types of anaemia.
- How to read it
- Blood B12 does not always reflect what is inside cells, so borderline results are sometimes followed by additional tests. Your doctor interprets it with your symptoms.
Usual units
ng/L (or pmol/L)
Commonly reported
Reference ranges vary by lab and assay
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHSCRP
C reactive proteinInflammation
- What it is
- A protein made by the liver that rises when there is inflammation anywhere in the body.
- Why it is measured
- It is a general marker of inflammation, used to help follow infections and inflammatory conditions.
- How to read it
- CRP is not specific to one cause, so a raised value tells your doctor there is inflammation, not where it is coming from. It is read with your symptoms.
Usual units
mg/L
Commonly reported
Commonly reported as low below about 5 mg/L (labs vary)
Reference ranges differ between laboratories and methods. Always compare a result against the range printed on your own report, and discuss it with your doctor.
NHS
Sources
- Blood tests NHS, 2023General explanations of common blood tests and what they measure.
- Diabetes fact sheet World Health Organization, 2024
- About cholesterol American Heart Association, 2024
Last reviewed: 2026-07-16