How to track your ALT over time

ALT is on almost every routine blood panel. It comes with the comprehensive metabolic panel and the liver panel, so most adults have years of ALT results without ever having asked for one. Most of the time it gets a glance and nothing more. That is a shame, because ALT is a test where the history says far more than any one result. A single mildly high value is common and often settles on its own. A value that has crept up over five years, while still inside the lab’s range, is easy to miss and worth knowing about.

What ALT measures

Alanine aminotransferase, or ALT, is an enzyme that works inside cells, mostly in the liver. When liver cells are inflamed or damaged, some of it leaks into the blood, and the level in a blood sample goes up. ALT is a marker of injury, not of how well the liver is working. A liver can be doing its job well with a high ALT, and a badly scarred liver can have a normal one.

ALT usually travels with AST, aspartate aminotransferase, a related enzyme. AST is found in the liver too, but also in muscle, the heart, the kidneys, and red blood cells, so ALT is the more liver-specific of the two. A 2024 review in American Family Physician describes ALT as the more specific marker of liver inflammation for that reason. Together the two are often called transaminases, or “liver enzymes”.

The numbers on the report

ALT is reported in units per liter, written U/L or IU/L. The two mean the same thing. Some labs outside the United States report enzyme activity in microkatals per liter (µkat/L) instead. One unit is a micromole of substrate converted per minute, and one katal is a mole per second, so:

U/L = µkat/L × 60

An ALT of 0.5 µkat/L is 30 U/L. If your history mixes the two, convert by hand before you chart it, or the line will drop by a factor of 60 at the switch.

Why the upper limit differs from lab to lab

Unlike A1c or cholesterol, ALT has no single cutoff that every lab prints. Each lab sets its own range from its own method and reference population, and ALT methods are not fully harmonized, which is one reason a CAP Today commentary argued that universal reference ranges are not yet workable. Upper limits on lab reports vary widely. Many sit well above what liver specialists now consider normal.

The American College of Gastroenterology’s 2017 guideline on abnormal liver chemistries, still the current version, set out a lower “true normal” ALT based on studies linking ALT to liver-related deaths:

The AASLD’s 2023 practice guidance on fatty liver disease repeats those values and adds a simpler rule of thumb: ALT above 30 U/L should generally be considered abnormal. It also notes that the normal values most labs print are higher than that.

So a result of 38 U/L can be unflagged on one lab’s report and above the guideline threshold at the same time. Neither is wrong. They answer different questions. The lab’s range describes the people the lab tested. The guideline range describes people without liver disease. If your clinician wants you to watch against the lower limit, chart against it.

Mild, moderate, and severe

Elevations are usually described as multiples of the upper limit of normal (ULN). The AAFP review calls two to five times the ULN mild. Very high values, in the hundreds or thousands, point to acute injury and are handled very differently. They are not what this post is about.

How often it is tested

There is no standard schedule for ALT on its own. Most people get it whenever a metabolic panel is drawn, which may be yearly, every few years, or every few months for someone with a chronic condition. It is checked more often when:

• A medication is known to affect the liver, such as methotrexate or some antifungals and tuberculosis drugs, where the prescriber sets a schedule.
• A previous result was high, to see whether it has come back down.
• Fatty liver disease or another chronic liver condition is being followed.

Statins are a common question. The FDA dropped routine periodic liver testing from statin labels in 2012, recommending a baseline before starting and further tests only when clinically needed, according to the 2017 AAFP review. If you take one, your ALT history is still worth having, and How to track your cholesterol over time covers the lipid side of the same record.

Because ALT is drawn so routinely, a long history may already exist in old portals, job physicals, and hospital visits. How to get all of your medical records covers requesting the older ones.

What counts as a real change

ALT varies a fair amount from draw to draw in the same healthy person. The EFLM Biological Variation Database, which pools the best studies, puts within-person variation for ALT at roughly 9 to 16 percent, with a combined estimate around 12 percent. That is higher than for cholesterol and much higher than for A1c.

Using the standard formula labs use for this, two results need to differ by roughly a third or more before the difference stands out from that noise. On an ALT of 30, a result anywhere from about 20 to 40 can be ordinary variation. A move from 30 to 38 is not a change worth reacting to on its own. A move from 22 to 60 is.

Single high results are common, and many do not hold up. The 2011 AAFP review notes that more than 30 percent of adults with an initially raised AST or ALT have normal levels on retesting. Not every elevation goes away, though, and the AASLD guidance treats ALT that is raised intermittently or persistently over six to twelve months as a sign of possible chronic liver injury. That is where a history helps most.

A few questions help sort it out:

• Is the move bigger than your usual spread? If your last five ALT results ran from 18 to 27, a 25 is not news. A 48 is.
• Is it a spike or a drift? One high value followed by a return to your usual level is often a one-off. Results that rise a little at a time, year after year, are easy to miss when each one is inside the lab’s range.
• Did AST move too? Look at both on the same date. See the next section.
• What happened in the week before the draw? Hard exercise, a new medication, a supplement, a heavy weekend. See the section after that.

The trend also matters when things go well. The AASLD guidance notes that a falling ALT tracks with improvement in fatty liver disease, including after weight loss. If you are making changes, a run of results is how you see whether they worked. Did the medication actually do anything? covers reading a before-and-after fairly.

ALT and AST together

The ratio of AST to ALT carries some information that neither has alone. The AAFP reviews summarize the classic pattern:

• AST/ALT below 1, with ALT higher, is typical of fatty liver disease.
• AST/ALT above 2 suggests alcohol-related liver disease.

The ratio is a clue, not a diagnosis. It is also why it is worth charting AST and ALT together. A high AST with a normal ALT can point away from the liver entirely, toward muscle or red blood cells.

Fatty liver disease and the new names

The most common causes of a mildly raised ALT are fatty liver disease and alcohol, according to the 2024 AAFP review. Fatty liver disease not caused by alcohol was long called NAFLD. In 2023, an international multisociety consensus renamed it metabolic dysfunction-associated steatotic liver disease, or MASLD. The inflammatory form, formerly NASH, is now MASH. A third label, MetALD, covers people with MASLD who also drink more than a set weekly amount. Older reports and notes will use the old names. They describe the same conditions.

Two things about ALT and MASLD are worth knowing:

• A normal ALT does not rule it out. The AASLD guidance says liver enzymes are frequently normal even in advanced disease, and should not be used alone to exclude it.
• ALT feeds into a fibrosis score. FIB-4 combines your age, AST, ALT, and platelet count to estimate the chance of significant liver scarring. The AASLD guidance uses it as a first step: below 1.3 is low risk, and above 2.67 makes advanced fibrosis likely. Your clinician calculates and interprets it. For tracking, it means the platelet count from the same blood draw is worth keeping alongside your ALT.

MASLD sits close to diabetes and high cholesterol, so an ALT history often belongs on the same timeline as your A1c and your lipids.

Things that move ALT

Plenty of things raise ALT without any lasting problem. Most are worth a note with the result.

• Hard exercise, especially weightlifting. In a study of healthy men who were not used to lifting weights, one hour of weightlifting raised both AST and ALT significantly, and they stayed raised for at least seven days. Muscle releases these enzymes too. A draw a few days after a hard session can look like a liver problem.
• Alcohol. Recent heavy drinking can push ALT and AST up, with AST often rising more.
• Medications. A long list of common drugs can raise ALT. The AAFP reviews include acetaminophen even at usual doses, NSAIDs, statins, some antibiotics and antifungals, methotrexate, amiodarone, valproic acid, and several antidepressants. Many of them cause only small rises. The AAFP review notes that raised ALT on a statin often resolves on its own.
• Supplements. Herbal and dietary supplements now account for about 20 percent of drug-related liver injury in the United States, according to an AASLD and NIH symposium report. The products most often implicated are bodybuilding supplements containing anabolic steroids, green tea extract, and multi-ingredient products. Brewed green tea is not the concern. Concentrated extract in capsules, often sold for weight loss, is.
• Weight change. Weight gain tends to raise ALT in people prone to fatty liver, and weight loss tends to bring it down.
• Other conditions outside the liver. Thyroid disease, celiac disease, and muscle disorders can all raise transaminases, the 2017 AAFP review notes. If your iron levels are high, a ferritin history belongs in the same picture, since iron overload is one of the causes clinicians check for.
• The sample itself. A hemolyzed sample, where red cells broke open in the tube, tends to affect AST more than ALT. If the report notes hemolysis, read the AST with that in mind.

Time of day matters less than often claimed. A large NHANES study found no clinically significant difference between morning and afternoon ALT in the U.S. population.

None of these mean the result is wrong. They mean it needs context next to it.

What to record with each result

For each ALT, keep:

ALT also goes by several names. Reports print it as ALT, SGPT, ALT (SGPT), Alanine Aminotransferase, Alanine Transaminase, and occasionally GPT. SGPT is the older name, from serum glutamic-pyruvic transaminase. Pick one name and use it everywhere, or your history will split into short, separate lines.

Charting it

A simple line chart works. A few choices make it honest:

• Draw the limit you are watching against. If your lab prints 0 to 55 and your clinician uses 33, shade 33. A chart against the wider range hides a slow climb.
• Put AST on the same chart. It shows whether the two move together, and which one leads.
• Space points by date. Results a week apart and results three years apart should not look evenly spaced.
• Mark medication and supplement changes, and any hard training block.
• Do not overreact to one point. With within-person variation this high, look for a run of results before you read a trend.

How to track your lab results over time has the general method for any test.

Tracking ALT in HealthViewer

HealthViewer is a lab results tracker that runs on your own computer. It imports ALT results from lab report PDFs, MyChart downloads, and direct connections to your health system, and files ALT, SGPT, ALT (SGPT), and Alanine Aminotransferase under one test. U/L and IU/L are treated as the same unit. Results in µkat/L are not converted, so multiply by 60 if you have any. Some labs use names like “Alanine Aminotransferase (ALT)” that can land as a separate test. Use Merge in the Test Catalog to combine them into one series.

In Trends, the Liver tag and the Liver Function Panel filter pull ALT, AST, ALP, bilirubin, and GGT together. The overlay view puts ALT and AST on one chart, and medication markers show where a statin or another drug started or stopped. Set your own upper limit as a custom range in the Test Catalog, and the chart shades that instead of the lab’s range. A journal note for a hard workout, a new supplement, or a lab switch shows up as a marker on the chart when you turn on Journal > Show journal.

Everything stays in an encrypted file on your computer, with no account and no cloud service. Getting Started walks through the first import.

This post is general information, not medical advice. Talk to your clinician about any raised ALT and before stopping or changing a medication or supplement.