ALT is the enzyme most specific to liver cells, released into blood whenever they are injured. It is the front-line test for fatty liver, hepatitis and medication-related liver stress.
Standard range versus optimal range
| Framework | ALT value | Source |
|---|---|---|
| Standard lab reference | about 7-56 U/L | Common laboratory range |
| Optimal, men | below 29-33 U/L | Prati updated healthy ranges |
| Optimal, women | below 19-25 U/L | Prati updated healthy ranges |
When it runs high
Elevated ALT means liver cells are leaking enzyme faster than they should. Mild rises under three times the upper limit most often reflect fatty liver or alcohol, while large rises point to viral hepatitis, drug injury or acute biliary blockage.
- Metabolic fatty liver disease, the most common cause in adults
- Alcohol
- Viral hepatitis B or C
- Medications including high-dose acetaminophen, statins in rare cases, and some supplements
- Celiac disease and autoimmune hepatitis
- Intense exercise, which can raise it briefly from muscle
When it runs low
Low ALT is generally benign and often simply reflects low muscle mass or low vitamin B6 status. Very low values in frail older adults have been linked to higher mortality, likely as a marker of reduced lean tissue rather than liver health.
- Low muscle mass or frailty
- Vitamin B6 deficiency
- Chronic kidney disease
- Normal variation, the usual explanation
The livers most faithful messenger
ALT lives densely packed inside liver cells, so even modest cell injury releases measurable amounts into the bloodstream. That specificity made it the workhorse of liver screening, and modern guidelines now prefer cutoffs far below the old laboratory upper limits. Research that defined truly healthy ranges found optimal ALT sits below about 30 U/L for men and below about 20 U/L for women, because values in the old normal range already predict fatty liver and future diabetes.
The silent fatty liver epidemic
Metabolic dysfunction-associated steatotic liver disease affects roughly a third of adults in developed countries, and ALT is usually its first laboratory whisper. The pattern is distinctive, a mild ALT rise alongside high triglycerides, low HDL and creeping fasting glucose. Combined with age and platelet count, ALT feeds the FIB-4 score that screens for liver fibrosis without a biopsy.
Bringing ALT down
Losing five to ten percent of body weight, cutting alcohol and treating insulin resistance normalize most mild elevations within months. Coffee consumption is consistently associated with lower ALT in observational data. A persistently elevated value deserves viral hepatitis screening, a medication and supplement review, and often an ultrasound, since ALT can look deceptively calm even in advanced disease.
Related calculators
Related biomarkers AST · GGT · ALP · Albumin