Alanine aminotransferase, a liver enzyme that rises when hepatocytes are stressed.
What it is
ALT (alanine aminotransferase, sometimes labelled SGPT) is an enzyme abundant in liver cells. Blood ALT in U/L rises when those cells are injured or leaky. Many UK labs use sex-specific upper reference limits.
ALT is enriched in hepatocyte cytoplasm; blood rises when cell membranes leak. It is the workhorse enzyme for detecting hepatocellular injury on UK GP and private panels.
Why it matters
ALT can rise with fatty liver disease, alcohol, viral hepatitis, medicines (including some antibiotics, antiepileptics, and high-dose supplements), and many other insults. Mild elevations are common; persistent or marked rises need clinical assessment, often with a full liver panel (AST, ALP, GGT, bilirubin) and history.
Lifestyle context: alcohol pattern, body weight, diabetes risk, and new medicines or herbal products. Do not stop prescribed drugs without advice because of one ALT result.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
ALT leaks from damaged hepatocytes into plasma. The liver’s roles in metabolism, detoxification, and protein synthesis mean significant injury can affect energy, clotting factors, and drug handling, which is why patterns and symptoms guide urgency.
For athletes
Athletes may see mild ALT rises after ultra-endurance events or with high body-mass changes. Anabolic steroid hepatotoxicity is a serious risk with unsupervised use. Fueling and alcohol in taper weeks still count, a “clean living” block before bloods helps interpretation.
