A liver function blood test, often called an LFT or liver blood test, measures a group of enzymes and proteins, mainly ALT, AST, ALP, GGT, bilirubin and albumin, that show how hard your liver is working. In the UK they're read against standard lab ranges. The test tells you something is putting your liver under load. It doesn't tell you what.
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What a liver function test actually measures
Forty-one. Trains five mornings a week, deadlifts heavy on Fridays. His private health panel came back with one line flagged in red: ALT, well above the range.
He'd already decided what it meant. His liver was packing in.
Before any of that, I wanted one thing.
What had he done in the 48 hours before the blood draw?
His heaviest session of the month. The night before.
That's not a liver giving up. That's a body that trained hard and then got measured. And it's the single most useful thing an LFT blood test won't tell you on the printout.
A liver function test, despite the name, doesn't measure how well your liver "functions" in any direct sense. It measures a handful of enzymes and proteins that change when the liver is under load. Six of them do most of the work. Two you'll hear about constantly. Four that fill in the picture so a report makes sense when it lands.
ALT and AST: the enzymes that leak when liver cells are stressed
ALT stands for alanine aminotransferase. It's an enzyme that mostly lives inside your liver cells. When those cells are irritated or damaged, ALT leaks into the blood and the level goes up (British Liver Trust, Liver blood tests).
AST, aspartate aminotransferase, does a similar job. One difference matters for active men: AST isn't only made in the liver. It's also made in your heart and your muscles. So AST can climb after hard physical effort for reasons that have nothing to do with your liver at all.
Hold onto that. It comes back later, and it changes how you read the whole test.
ALP and GGT: the drainage markers, and GGT's alcohol link
ALP, alkaline phosphatase, is found mostly in your liver and your bones. A raised ALP can point to a problem with the bile ducts, the drainage plumbing of the liver, rather than the liver cells themselves.
GGT, gamma-glutamyl transferase, sits alongside it. When ALP and GGT go up together, that pattern suggests a bile-flow issue rather than cell damage (NHS Specialist Pharmacy Service, Interpreting liver blood tests).
GGT has a second feature worth saying plainly, without moralising. It's sensitive to alcohol and to some medications. A raised GGT can reflect recent drinking. It can also reflect a drug you take every day. On its own, it's a signal, not a sentence.
Bilirubin and albumin: clearance and capacity
Bilirubin is the pigment made when old red blood cells are broken down. A healthy liver clears it. If bilirubin rises far enough, that's the yellowing of the skin or eyes people call jaundice, and that's a same-week GP visit, not a wellness read.
Albumin is a protein the liver makes. It's a rough gauge of the liver's manufacturing capacity over time. Low albumin is read in context, alongside everything else.
Six markers. Two questions, really. Are the liver cells irritated, and is the drainage working? The rest is detail.
Why your GP ordered it, or why your panel includes it
You probably didn't go looking for a liver function test in the UK. Something put it in front of you.
On the NHS, the common triggers are routine: a general health check, a fatigue work-up, monitoring for a medication you're on, a review after mentioning your drinking. It's a cheap, fast, informative panel, so it gets added to a lot of blood forms.
On a private panel, it usually arrives bundled. A full men's health check. An athlete or recovery panel. A full screen you bought yourself in January.
Either way, you ended up holding liver function test results you didn't ask for, with an explanation that was probably "a bit raised" or "within range". Neither answers the question you actually have.
The question is simpler than the report makes it look. Is this number a problem, or is it noise?
What counts as "normal": the UK ranges
This is the section search engines quote and AI assistants extract, so here it is plainly. These are common UK adult reference ranges. Your own lab's range, printed next to your result, is the one that counts.
ALT: 0 to 40 IU/L
AST: 0 to 40 IU/L
GGT: 0 to 50 IU/L
Bilirubin: 5 to 21 micromol/L
Albumin: 35 to 50 g/L
ALP: varies more than the others by lab and assay, so read it against the range on your own report.
Those four firm ranges come from NHS clinical guidance (NHS Specialist Pharmacy Service, Interpreting liver blood tests). Two things to hold in mind when you read them.
First, lab ranges vary slightly between providers. "Normal" is a population band, not a personal optimum. It's the same trap that catches men reading a testosterone result: the range was built to flag illness, not to describe where you function best. We pull that thread fully in the myth of the normal range.
Second, a single reading after anything acute is not a baseline. A hard session in the last 48 hours. A heavy weekend. A recent viral illness. A new medication or supplement. Any of those, and the snapshot is measuring the event, not your liver. Retest in 4 to 8 weeks when nothing acute is going on.
What a raised result usually means in active men
Here's the part most explainers get wrong by listing every possible cause as if each were equally likely. In an otherwise well man between 35 and 50, the realistic shortlist is short. And the most common entries on it are not liver disease.
A hard training block (yes, exercise can raise ALT and AST)
Start here, because it's the one nobody mentions.
In a study of healthy men who did an hour of weight training, ALT and AST were measurably raised for at least 7 days afterwards, with the muscle markers climbing even higher (Pettersson et al., 2008, British Journal of Clinical Pharmacology, Muscular exercise can cause highly pathological liver function tests in healthy men).
Read that back. A week. From one heavy session.
So the man who deadlifts on Friday and gets bloods on Saturday can walk away convinced his liver is failing, when what he's actually measuring is Friday. It's not a liver problem. It's a timing problem.
The answer is boring and effective: don't test within a few days of heavy training, and if a result is high and you trained hard beforehand, retest after a proper rest before drawing any conclusion.
Alcohol: what the markers actually reflect
Alcohol shows up mostly through GGT, and sometimes through the ratio between AST and ALT. That's it. The test doesn't read your weekend back to you in detail, and it isn't there to shame you.
The reference point worth knowing is the UK guideline. The Chief Medical Officers advise not regularly drinking more than 14 units a week, spread over three or more days (UK Chief Medical Officers, 2016, Low risk drinking guidelines). Fourteen units is roughly six pints of average-strength beer or a bottle and a half of wine.
If your GGT is up and you want a cleaner read, a few weeks off the drink before a retest tells you how much of the number was the alcohol.
Fatty liver (MASLD): the common one no one mentions
This is the cause that hides in plain sight. MASLD, the condition formerly called NAFLD, is estimated to affect up to 1 in 5 people in the UK, and it often has no symptoms for years (British Liver Trust, MASLD, NAFLD and fatty liver disease).
It's closely linked to carrying extra weight and to type 2 diabetes. The good news is that it's one of the more responsive things on this list to lifestyle change. The important part: a liver function test cannot diagnose it, and neither can we. A pattern that raises the question is a reason to talk to your GP, not a reason to buy a supplement.
Medications and supplements
Plenty of everyday things touch liver markers. Paracetamol. Statins. Some over-the-counter "liver support" products.
One firm line here, because it's a compliance and a safety point at once: no supplement protects, heals, or detoxes your liver in any way a blood test would reward. If a product claims it does, that claim is the problem. If you take regular medication, your GP is the one who monitors what it does to your bloods.
The other half: when it isn't lifestyle
Sometimes the answer isn't training, drink, weight, or a tablet.
Viral hepatitis. An autoimmune condition. A problem with the bile ducts. These are real, they're a minority of cases in well men, and they are not things you sort out with discipline.
The line is simple. If you've checked the obvious drivers, given it a proper retest window, and the numbers won't settle, that's the conversation to have with your GP, not with us.
What a single abnormal reading does NOT tell you
If you take one thing from this, take this.
An abnormal liver function test is not a diagnosis of liver disease. It's very common to have results that aren't normal, and the British Liver Trust notes that in almost 1 in 3 cases they go back to normal by themselves within about 3 weeks (British Liver Trust, Liver blood tests).
A mildly raised ALT is one of the most common findings on routine bloods. On its own, in a man who feels well, it usually isn't the dramatic story Google sold him in the first eight minutes.
The markers are read together, as a pattern, over time. One number, on one morning, after one hard week, is the start of a question. Not the answer.
What changes when you actually have the number
The value of an LFT isn't the single result. It's what you do with it next.
Without a baseline, you're guessing. You cut back the wine, you deload for a fortnight, you drop a few pounds, and you've no idea whether any of it moved the number.
With a baseline, interpreting a liver function test becomes a loop instead of a verdict. Change one variable. Give it 4 to 8 weeks, longer for weight. Retest. Read the delta.
And it's yours. Your blood data is your record. If you ever take it to a GP, for a referral or a second opinion, you arrive with a timeline instead of a single morning's number. That's something an eight-minute appointment isn't built to assemble for you.
How Andro Prime will measure this: join the waitlist
Straight with you here: there's no liver panel to sell you today.
A liver test is on the Andro Prime roadmap. The same model as the rest of our kits when it lands: a finger-prick sample at home, a UKAS-accredited lab, and results in plain English with a recommendation built on GP-standards logic and reviewed by our medical lead. No jargon-only printout. No "a bit raised, retest in a few months" with nothing to act on.
If that's what you've been missing, join the waitlist. You'll be first when it launches, and you'll get a founding-customer offer.
Your next move
If you only read this section: an LFT measures ALT, AST, ALP, GGT, bilirubin and albumin against UK lab ranges. In active men, a raised result is most often hard training, alcohol, fatty liver, or a medication, not liver disease. A single reading is rarely the answer; the retest is. Jaundice, upper-right abdominal pain, or a markedly raised enzyme is a GP visit, not a wellness read.
So here's the question.
You've got a number, or you're about to get one. It'll sit on the page and explain nothing. You can read the worst into it for a quarter, or you can find out what it's actually doing: rest properly, sort the obvious drivers, retest in two months, and read the direction.
What was the last thing your blood test actually told you, and did anyone help you read it?
Be first to test your liver markers with Andro Prime. A liver panel is coming: finger-prick at home, UKAS-accredited lab, results in plain English with a GP-standards recommendation. Join the waitlist for early access and a founding-customer offer.
System DB // References
- British Liver Trust. Liver blood tests (formerly LFT). https://britishlivertrust.org.uk/information-and-support/living-with-a-liver-condition/liver-blood-tests/
- British Liver Trust. MASLD, NAFLD and fatty liver disease. https://britishlivertrust.org.uk/information-and-support/liver-conditions/masld-nafld-and-fatty-liver-disease/
- NHS Specialist Pharmacy Service. Assessing liver function and interpreting liver blood tests. https://www.sps.nhs.uk/articles/assessing-liver-function-and-interpreting-liver-blood-tests/
- Pettersson, J. et al. (2008). Muscular exercise can cause highly pathological liver function tests in healthy men. British Journal of Clinical Pharmacology 65(2): 253–259. https://pubmed.ncbi.nlm.nih.gov/17764474/
- UK Chief Medical Officers (2016). Low risk drinking guidelines. https://www.gov.uk/government/publications/alcohol-consumption-advice-on-low-risk-drinking
Frequently asked questions
What is a liver function blood test?
A liver function blood test, often called an LFT or liver blood test, measures a group of enzymes and proteins in your blood, mainly ALT, AST, ALP, GGT, bilirubin and albumin. Together they show how hard your liver is working and whether something is putting it under load. In the UK these are read against standard lab ranges. The test flags that there's a signal. It doesn't tell you the cause on its own.
What does a liver function test measure?
Six markers do most of the work. ALT and AST are enzymes that leak from liver cells when they're stressed or irritated. ALP and GGT are linked to the bile drainage system, and GGT also rises with alcohol and some medications. Bilirubin is the pigment your liver clears; albumin is a protein it makes. Read together, they describe whether the problem is liver-cell irritation, a bile-flow issue, or neither.
What is a normal liver function test range in the UK?
Common UK adult ranges are roughly: ALT and AST 0 to 40 IU/L, GGT 0 to 50 IU/L, bilirubin 5 to 21 micromol/L, and albumin 35 to 50 g/L (NHS Specialist Pharmacy Service). ALP varies more than the others by lab and assay, so read it against your own report's printed range. Lab ranges differ slightly between providers, which is why you always check the number against the range printed next to it, not a number from the internet.
What does a high or abnormal liver result mean?
Usually less than people fear. The British Liver Trust notes it is very common to have liver blood test results that aren't normal, and that in almost 1 in 3 cases the results return to normal by themselves within about 3 weeks. In active men, a raised ALT or AST is often a hard training block, alcohol, fatty liver, or a medication. It's a signal to look at, not a diagnosis. Persistent or markedly raised results are a GP conversation.
Can exercise raise liver enzymes?
Yes, and this is the thing most explainers miss. A hard resistance session can raise ALT and AST for at least 7 days afterwards in healthy men (Pettersson et al., 2008, British Journal of Clinical Pharmacology). AST in particular also comes from muscle. So a blood draw taken a day or two after heavy training can show 'liver' numbers that are really muscle recovery. If you trained hard before the test, that's worth knowing before you panic.
Does alcohol show up on a liver blood test?
It can, mainly through GGT, an enzyme that's sensitive to alcohol and to some medications. A raised GGT on its own doesn't prove how much you drink, and it isn't a verdict on your liver. It's one marker read alongside the others. The UK Chief Medical Officers' low-risk guideline is not to regularly drink more than 14 units a week, spread over three or more days. If you want a cleaner reading, a few weeks off the drink before a retest helps.
Can a single abnormal liver result be wrong?
It's rarely a lab error, but a single reading is often misleading on its own. Recent heavy training, a few big nights, a new medication or supplement, or a recent illness can all nudge the numbers. Liver markers are read as a pattern, over time, not as a one-off verdict. A result you've retested 4 to 8 weeks later, when nothing acute is going on, tells you far more than the first snapshot.
When should I see a GP about a liver result?
See your GP promptly if you have jaundice (yellowing of the skin or eyes), dark urine or pale stools, persistent pain in the upper-right abdomen, or a markedly raised enzyme (for example ALT more than three times the upper limit), especially if you feel unwell. Also go to your GP, not us, if you already have a known liver condition or you're on regular medication that needs monitoring. We explain what the number means. We don't diagnose and we don't treat: that's your GP's job.