Alpha-Fetoprotein (AFP) Unit Converter
Alpha-Fetoprotein (AFP) Unit Converter
Convert alpha-fetoprotein between ng/mL, µg/L, pmol/L and WHO IU/mL, with the adult reference limit, the 400 ng/mL hepatocellular carcinoma threshold, and why a normal AFP excludes very little.
Alpha-Fetoprotein (AFP) converter
Mass ⇄ molar ⇄ IUAlpha-fetoprotein 6.5 ng/mL in a non-pregnant adult
Formula and conversion factors
pmol/L = ng/mL × 14.4928
IU/mL = ng/mL ÷ 1.21
- ng/mL = µg/L
- a nanogram per millilitre and a microgram per litre are the same concentration, so no arithmetic is involved between them
- 14.4928
- derived from a molecular mass of 69,000 Da. Molar reporting is not used clinically and no published threshold is expressed in pmol/L
- 1.21
- the WHO International Standard states that 1 IU is approximately 1.21 ng of AFP, with a stated range of 1.02–1.43 ng, so IU/mL and ng/mL results are not interchangeable to better than roughly 20 per cent
- assay dependence
- AFP immunoassays differ in antibody and calibration; serial results should be followed on one platform, since a change of laboratory can shift the number without any change in the patient
Worked example
Alpha-fetoprotein 6.5 ng/mL in a non-pregnant adult
6.5 ng/mL = 6.5 µg/L — the two units are identical
6.5 × 14.4928 = 94.2 pmol/L
6.5 ÷ 1.21 = 5.37 IU/mL
Within the adult non-pregnant reference interval of 0–10 ng/mL
Thresholds across the units
| ng/mL | pmol/L | IU/mL | |
|---|---|---|---|
| Adult reference interval, not pregnant | 0 – 10 | 0 – 145 | 0 – 8.3 |
| Range often seen in chronic hepatitis or cirrhosis without cancer | 10 – 100 | 145 – 1,449 | 8.3 – 82.6 |
| Threshold strongly suggestive of hepatocellular carcinoma in a cirrhotic patient with a liver lesion | 400 | 5,797 | 331 |
What AFP can and cannot do in hepatocellular carcinoma
| Threshold | Pooled sensitivity | Pooled specificity |
|---|---|---|
| 20 – 100 ng/mL | ~61% | ~86% |
| 200 ng/mL | ~49% | ~98% |
| 400 ng/mL | ~32% | ~99% |
Three units, one clinically useful one
Alpha-fetoprotein is reported in ng/mL in most laboratories and in µg/L where SI units are preferred. Those two are the same number, so nothing has to be calculated between them. A molar column in pmol/L uses a factor of 14.4928 derived from a molecular mass of 69,000 daltons, and is offered for completeness only — no clinical threshold anywhere is written in molar units. AFP is also standardised against a WHO International Standard, in which one international unit is approximately 1.21 ng, with a stated range of 1.02 to 1.43. That spread matters: a result converted between IU/mL and ng/mL should not be trusted to better than about twenty per cent.
In a non-pregnant adult the upper reference limit is around 10 ng/mL, but the region just above it is crowded with benign explanations. Chronic hepatitis B and C, cirrhosis of any cause, and regenerating liver after injury all raise AFP into the tens or low hundreds without a tumour being present, and the level tends to fluctuate with hepatic inflammation. A single mildly raised AFP in someone with known liver disease is a reason for imaging and a repeat, not for alarm.
The figure that changes management is 400 ng/mL. In a patient with cirrhosis and a focal liver lesion, an AFP above that level is strongly suggestive of hepatocellular carcinoma, with a pooled specificity of about 99 per cent. The reverse does not hold. Pooled sensitivity at 400 ng/mL is only around a third, so the majority of hepatocellular carcinomas are missed by AFP alone, and surveillance in cirrhosis is built on six-monthly ultrasound with AFP as an adjunct.
AFP is not only a liver marker. It is produced by non-seminomatous germ cell tumours, where it is measured alongside hCG and LDH for staging and for following response, and a raised AFP effectively excludes pure seminoma. It rises physiologically through pregnancy, where maternal serum AFP is reported as a multiple of the median in screening for neural tube and abdominal wall defects, and it is very high in healthy neonates, falling over the first year. No AFP result interprets itself: it belongs to a clinician who has the imaging, the history and the context.
Frequently asked questions
How do I convert AFP from ng/mL to pmol/L?
Multiply by 14.4928, a factor derived from a molecular mass of 69,000 daltons. An AFP of 6.5 ng/mL is 94.2 pmol/L. Molar reporting is rare and no clinical threshold uses it — ng/mL and the identical µg/L are the working units.
How do IU/mL and ng/mL relate for AFP?
The WHO International Standard sets 1 IU at approximately 1.21 ng of AFP, so ng/mL divided by 1.21 gives IU/mL. The standard states a range of 1.02 to 1.43 ng per IU, which means a converted result carries about 20 per cent uncertainty and the two conventions are not fully interchangeable.
What is a normal AFP?
In a non-pregnant adult, roughly below 10 ng/mL, though laboratories differ. The interval does not apply in pregnancy, where AFP rises with gestation and is reported as a multiple of the median, nor in infants, whose levels are very high at birth and fall over the first year.
Does a normal AFP mean I do not have liver cancer?
No. Pooled sensitivity at the 400 ng/mL threshold is only about a third, and many hepatocellular carcinomas never secrete AFP. That is why surveillance in cirrhosis uses six-monthly ultrasound with AFP as an adjunct, and why a normal result is never treated as an all-clear on its own.
What raises AFP apart from cancer?
Chronic hepatitis B and C, cirrhosis of any cause and hepatic regeneration after injury commonly push AFP into the tens or low hundreds. Pregnancy raises it physiologically. Any raised result needs a clinician to read it alongside imaging and the clinical picture.
Related calculators
References
- Singal AG, Llovet JM, Yarchoan M, et al. AASLD Practice Guidance on prevention, diagnosis, and treatment of hepatocellular carcinoma. Hepatology. 2023;78(6):1922–1965.
- Zhang J, Chen G, Zhang P, et al. The threshold of alpha-fetoprotein (AFP) for the diagnosis of hepatocellular carcinoma: a systematic review and meta-analysis. PLoS One. 2020;15(2):e0228857.
- WHO International Standard, Alpha-Fetoprotein, Human (2nd International Standard, NIBSC code 22/216). Instructions for use: 1 IU ≈ 1.21 (1.02–1.43) ng.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.