What is an optimal ALT level?
The short answer
An optimal ALT level is under 30 U/L. That is Dr. Peter Attia's number. You can watch him say it below.
Most labs call ALT high only above 55. So your report can call 43 normal while it sits above where he draws the line.
“now the general rule of thumb is that you would like to see an A and ALT both below about 30 IU per liter”
Where a number lands, and who said so
- under 30 U/L The range Dr. Peter Attia draws
- 30–55 U/L Normal on most reports. Above optimal Dr. Peter Attia · 17:32 →
- over 55 U/L Most labs flag this as high
What ALT measures
An enzyme concentrated inside liver cells.
Stressed or damaged liver cells leak it into the blood. That makes it one of the most direct signals of liver strain.
Checked against MedlinePlus — ALT Blood Test.
One of the doctors we cite, on why it matters
“if your alt is High it usually means you have liver fat doesn't tell you why you have liver fat but it usually means you have liver fat”
Common questions
What is an optimal ALT level?
Under 30 U/L, according to Dr. Peter Attia.
What is a normal ALT level?
Most US labs print 0–55 U/L. Your report grades you against that range. It exists to catch disease, not to describe your best.
What does your ALT number mean?
Under 0 U/L, your report marks it low. Between 0 and 55 it prints as normal. Over 55, your report marks it high. Where the people we follow draw their own line is above.
Is ALT of 43 normal?
Your lab will call it normal. Dr. Peter Attia puts the ceiling at 30 U/L, so by that number it is high.
Do they all agree?
No. Dr. Robert Lustig puts the line somewhere else: “the upper limit of alt should be 25 when I entered medical school in 1976 the upper limit for alt was 25”
What does the ALT test measure?
An enzyme concentrated inside liver cells. Stressed or damaged liver cells leak it into the blood. That makes it one of the most direct signals of liver strain.
Where does this number come from?
Dr. Peter Attia, on video. The link above jumps straight to that minute.
They don't all draw the line in the same place
“the upper limit of alt should be 25 when I entered medical school in 1976 the upper limit for alt was 25”