ALT (SGPT) Unit Converter
ALT (SGPT) Unit Converter
Convert alanine aminotransferase between U/L, IU/L, µkat/L and nkat/L, with the updated sex-specific upper limits.
ALT (SGPT) converter
Activity unitsALT 42 U/L
Formula and conversion factor
U/L = µkat/L × 60
- U
- 1 unit = 1 µmol of substrate converted per minute
- kat
- 1 katal = 1 mol of substrate converted per second
- ÷ 60
- the only difference between the two is per-minute versus per-second
- IU/L
- numerically identical to U/L
Worked example
ALT 42 U/L
42 ÷ 60 = 0.700 µkat/L
= 700 nkat/L = 42 IU/L
Reference ranges and interpretation
| Men | Women | |
|---|---|---|
| Contemporary upper limit | 33 U/L | 25 U/L |
| Older conventional limit | 40 – 55 U/L | 33 – 45 U/L |
| In µkat/L | 0.55 | 0.42 |
What ALT measures
Alanine aminotransferase is the most liver-specific of the routine enzymes. It sits in hepatocyte cytosol and leaks into plasma when cell membranes are damaged, so the height of the rise broadly tracks the extent of acute hepatocyte injury.
What counts as normal has been revised downward. Older reference intervals were derived from populations that included people with undiagnosed fatty liver and hepatitis C, which inflated the upper limit. Contemporary healthy-donor studies put it closer to 33 U/L in men and 25 U/L in women, and several guidelines now recommend these lower thresholds. A patient told for years that an ALT of 45 was normal may have had unrecognised steatohepatitis.
The magnitude of elevation narrows the differential usefully. Values above about 1000 U/L come from a short list: ischaemic hepatitis, paracetamol or another drug, acute viral hepatitis, and occasionally acute biliary obstruction from a stone. Modest elevations of two or three times the upper limit are far commoner and are dominated by fatty liver disease, alcohol and medication. A normal ALT does not exclude cirrhosis — enzymes often fall as functioning hepatocyte mass is lost.
Frequently asked questions
How do I convert ALT from U/L to µkat/L?
Divide by 60. A unit is one µmol per minute and a katal is one mol per second, so the conversion is simply per-minute to per-second. An ALT of 42 U/L is 0.700 µkat/L.
Is IU/L the same as U/L?
For reporting purposes, yes — the two are used interchangeably and are numerically identical on modern standardised methods.
What is a normal ALT?
Contemporary healthy-population studies suggest up to about 33 U/L in men and 25 U/L in women. Many laboratories still quote older, higher limits derived from populations including undiagnosed fatty liver.
How high does ALT go in paracetamol overdose?
Often into the thousands, peaking around 72 hours. Values above 1000 U/L narrow the differential to ischaemia, drugs, acute viral hepatitis or acute biliary obstruction.
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References
- Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: evaluation of abnormal liver chemistries. Am J Gastroenterol. 2017;112(1):18–35.
- IFCC reference procedure for the measurement of catalytic activity of alanine aminotransferase at 37°C.
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.