Liver and organ health
Normal ALT and AST Levels by Age, for Men and Women
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed August 20267 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
QUICK ANSWER
UK labs print one ALT range and one AST range for every adult age. Age still moves them. In a study of 1.37 million samples, 20% of men aged 25 to 34 had a raised ALT, against 6.7% of men aged 65 to 74. In women, a raised AST becomes twice as common around 50.
Not sure which markers you need? Build your test →Your ALT reads 46. The range printed beside it stops at 41. You are 29, you feel fine, and nobody has explained why the number is flagged. The question that follows is fair: is 46 a problem, or is it what 29 looks like?
This guide covers what liver enzymes do across adult life, how much ALT and ALP move with age and sex, and when a result is worth a GP conversation rather than a worried evening. Of all the liver enzymes, ALP moves most across the decades, and a raised adult ALP is as often bone as liver.
1. What counts as a normal liver enzyme level?
A typical UK adult ALT range runs to about 41 U/L, and ALP sits near 30 to 130 U/L. Ranges differ between labs, so read yours against the range printed on your own report.
ALT stands for alanine aminotransferase. It is an enzyme that leaks into the blood when liver cells are stressed, which makes it the most liver-specific of the group. ALP, or alkaline phosphatase, comes from the liver and from bone. That second source matters later.
“Initial investigation for potential liver disease should include bilirubin, albumin, ALT, ALP and GGT, together with a full blood count if not already performed within the previous 12 months.”
— British Society of Gastroenterology, Guidelines on the management of abnormal liver blood tests (Gut, 2018)
Those five markers are the standard set, read together rather than one at a time. Our liver function test guide walks through what each one does, and our milk thistle guide covers the supplement people most often take to move them. Glutathione is the newer one on the same shelf.
2. Do liver enzymes change with age?
Yes, and ALT changes more than most people expect. A 2022 analysis in Clinical Gastroenterology and Hepatology read 1,369,180 blood samples from 601,779 people. It found what the authors called an extreme age dependence in men.
| Age band | Men flagged as raised | What that suggests |
|---|---|---|
| 25 to 34 | 20.0% | One young man in five is flagged |
| 65 to 74 | 6.7% | The same limit flags far fewer |
The same paper tracked the 95th centile for ALT in men. It ran above 80 U/L at age 35 and dropped below 50 U/L by 75. Nothing about the printed limit changes across those forty years.
Women follow a different pattern. The age effect on ALT is much weaker in women. AST goes the other way: the share of women with a raised AST roughly doubles around age 50, from about 6% to about 12%. GGT climbs throughout life in women, and up to about age 60 in men.
3. What is a normal AST level at your age?
Most UK labs set the top of the adult AST range somewhere between 34 and 50 U/L. The same range applies at 25 and at 75. U/L means units of enzyme activity in a litre of blood.
AST stands for aspartate aminotransferase. Like ALT, it leaks into the blood when cells are under strain. Unlike ALT, it is also found in muscle and the heart. So a hard workout before your test can lift it, and on its own it says less about the liver.
| NHS lab | Adult AST range |
|---|---|
| North Bristol NHS Trust | Men under 50 U/L, women under 35 U/L |
| Royal Cornwall Hospitals | 5 to 34 U/L, from age 19 |
| North West London Pathology | 40 U/L or under |
The clearest age pattern for AST is in women. In the 1.37 million sample study above, the share of women with a raised AST doubled around age 50, from about 6% to about 12%.
Age also enters AST through a score. FIB-4 combines your age, AST, ALT and platelet count to estimate the chance of liver scarring. Because age sits inside the formula, the score climbs as you get older even when your enzymes stay put.
A 2017 study in the American Journal of Gastroenterology found the usual cut-off wrongly flagged most people aged 65 and over. It proposed 2.0 for that age group instead. Our FIB-4 calculator applies that adjustment.
Many NHS labs no longer run AST routinely. North Bristol lists it as rarely indicated, and the BSG starter set quoted above leaves it out. Helvy panels do not measure AST either. ALT is the liver enzyme we report.
4. Why do men and women get different limits?
Men carry more muscle and more liver mass, so their enzyme levels run higher on average. Most labs already build sex into the ALT limit. Almost none build in age. The 2022 analysis put it plainly: upper limits for ALT, AST and GGT generally take sex into account, but not age.
Its conclusion was that age adaptation should be considered, because the current setup sends a large share of young men for follow-up tests they may not need.
There is a counter-argument worth knowing. The BSG guideline notes that the current upper limit for ALT may be too high, because the people used to build those ranges included some with undetected fatty liver. So one camp says the limit is too low for young men, and another says it is too high for everyone. Both are arguing that a single printed number is doing too much work.
ALP behaves differently from the two enzymes above. Our guide to a high ALP with normal liver function covers it on its own.
5. Why does ALP rise as you get older?
Usually because of bone, not liver. ALP is made in both places, and bone turnover speeds up after the menopause. A rising ALP in an older woman is often a bone signal wearing a liver label.
A 2015 study in Aging Clinical and Experimental Research measured ALP in 626 postmenopausal women with osteoporosis. Levels in women in their eighties were significantly higher than in women in their sixties. ALP tracked bone-specific ALP far more closely than it tracked liver markers.
This is why a raised ALP is read alongside GGT. If GGT is normal, the source is more likely bone. Our ALP guide covers that pairing in full.
6. When does a raised enzyme actually matter?
One reading rarely settles anything. Enzymes move with a heavy weekend, a virus, a new medication or a hard training block. A repeat test weeks later tells you far more than the first one did.
How far over the line you are matters as much as the flag itself, and our guide to high ALT levels breaks that down. These patterns are worth a GP conversation at any age:
- A raised ALT that is still raised on a repeat test.
- An ALT well above the limit rather than a few points over.
- A raised ALP alongside a raised GGT.
- Yellowing of the skin or eyes, or dark urine.
- Regular drinking above the UK guideline of 14 units a week.
- A falling albumin, which reflects how the liver is working.
The reverse also holds, and it is the part people miss. Normal enzymes are not an all-clear. That is clearest in fatty liver, where most people test inside the normal range. The BSG guideline notes that many people with significant liver scarring have enzymes inside the reference range. The NHS makes the same point about symptoms: most types of liver disease do not cause any symptoms in the early stages.
That is why the BSG set above pairs the liver markers with a full blood count. A blood test measures markers and offers wellness insight. It does not diagnose, and a qualified clinician reads the set together.
7. Which blood test shows your liver enzymes
Helvy's Thyroid & Vital Organs panel (£159) reports ALT, ALP, albumin and total protein, alongside thyroid, kidney and full cholesterol markers. It is a home finger-prick test, processed by UKAS-accredited UK labs.
It does not include GGT, AST or bilirubin. Those are part of the standard NHS set, so if a clinician wants the full picture, ask your GP for them.
One reading places you today. Two readings, months apart, show the direction, which is the thing that actually matters. To assemble your own marker list, the build-my-test tool walks you through it.
READY TO TEST?
Know your liver trend, not just today's number
Helvy's home blood tests report ALT, ALP, albumin and total protein with plain-English context, so a result a few points over the line never sparks a needless panic. Samples are processed by UKAS-accredited UK labs. Albumin follows the same pattern, covered in albumin levels by age, with a below-range result in low albumin levels.
Frequently asked questions
Is there an official liver enzyme chart by age in the UK?
No. UK labs print one adult range at every age, usually split by sex for ALT. Population data does show a clear age pattern, but that is an average rather than an age-specific normal range. Read your result against the range on your own report.
What is a normal AST level by age?
UK labs use one adult AST range at every age. The upper limit sits between about 34 and 50 U/L, depending on the lab and your sex. In a study of 1.37 million samples, a raised AST became twice as common in women around age 50.
Is an ALT of 46 normal for a man in his twenties?
It is common at that age. In a study of 1.37 million samples, 20% of men aged 25 to 34 had an ALT above the standard limit, against 6.7% of men aged 65 to 74. Common is not the same as harmless, so repeat the test and ask a qualified clinician to read it in context.
Do liver enzymes go up or down with age?
It depends on the enzyme. ALT falls in men after about 35. AST rises in women around 50. GGT climbs throughout life in women and up to about 60 in men. ALP tends to rise with age, largely because of bone turnover.
Why is my ALP high but my liver fine?
ALP is made in bone as well as liver. After the menopause, bone turnover speeds up and ALP follows. In a study of 626 postmenopausal women, ALP tracked bone activity far more closely than liver markers. Clinicians usually read ALP alongside GGT to tell the two sources apart.
Should I worry about one raised liver enzyme reading?
One reading rarely means much on its own. Alcohol, a virus, a new medication and a hard training block all move these numbers. Repeat the test after a few weeks. A result that stays raised is the one to take to your GP.
Do normal liver enzymes mean my liver is healthy?
Not on their own. The BSG guideline notes that many people with significant liver scarring have enzymes inside the reference range. The NHS says most types of liver disease cause no symptoms in the early stages. Enzymes are one input, not a verdict.
Related guides
Liver Function Test UK
ALT, ALP, GGT, bilirubin and albumin explained, with UK ranges.
ALT Blood Test UK
What a raised ALT means, and the everyday things that lift it.
ALP Blood Test UK
Why a high alkaline phosphatase is often bone rather than liver.
GGT Blood Test UK
The enzyme that tells bile-duct and alcohol signals apart.
Blood Test Reference Ranges UK
Why 'normal' on a lab report is a population range, not a target.
Thyroid & Vital Organs Test
Liver, kidney, thyroid and cholesterol markers in one home test.
Related panels
Keep reading