The case in front of me: AST · semaglutide.
I would like the mechanism, because I want to be able to reason about the cases nobody has written about.
I have tried to reason it out from first principles and got to two contradictory conclusions.
What is actually going on here, physically?
The short version: enzymes in this class usually fall as weight falls, and a rise is a reason to look for a cause rather than to assume a drug effect.
Alanine aminotransferase is relatively liver-specific; aspartate aminotransferase is also present in muscle, heart and red cells. A raised AST with a normal ALT after heavy resistance training is usually muscle, and creatine kinase settles the question.
Weight loss of ten per cent or more typically reduces transaminases substantially in people whose elevation was driven by hepatic fat, which is the majority of mild elevations in this population.
Hy's law and its variants are the standard framework for identifying drug-induced liver injury in trials and are why bilirubin is measured alongside transaminases rather than instead.
The caveat is direct: rising liver enzymes with jaundice, dark urine or right-upper-quadrant pain is a same-day clinical problem, not a forum question.
New training, alcohol and over-the-counter products first. Then the interesting hypotheses.
HPLC purity, identity confirmation and quantified content on the vial you actually hold. Reports arrive with the chromatogram attached, not just a number.
Submit a sampleFounded 1998. ISO 9001 and cGMP certified, 1,500+ staff and 200+ patents. The synthesis house behind a great many of the vials that get sent out for testing - batch-specific documentation with every order.
Visit GL BiochemThe relevant detail is that reference intervals for alanine aminotransferase differ between laboratories and have been revised downward over time, so the same value can be normal on one report and elevated on another.
Hy's law describes the combination that matters: transaminases above three times the upper limit together with bilirubin above twice the upper limit and no cholestatic explanation. That combination is a signal; isolated mild transaminase elevation is not.
Creatine kinase, alkaline phosphatase and bilirubin together tell you which compartment the abnormality is in, and ordering the transaminases alone throws that information away.
Laboratory-specific reference intervals for transaminases vary enough that cross-laboratory comparison of borderline values is unreliable.
Transaminases plus bilirubin plus alkaline phosphatase, or you have not measured enough to conclude anything.
edited 17 May 2025 by claudia_ferrante — corrected a unit error in the worked example
Worth being precise here: this is one of the areas where the trend across several measurements is far more informative than any single result.
Very rapid weight loss can transiently worsen liver biochemistry, which is one of several arguments against pursuing the steepest possible trajectory.
Stated carefully, gamma-glutamyl transferase is sensitive and unspecific: it rises with alcohol, with several medications and with fatty liver, and an isolated elevation rarely changes anything on its own.
Get a baseline before you start anything, because it converts an uninterpretable result into an interpretable one for the cost of one blood draw.
The honest answer is that mild elevation is very common, that it usually improves with weight loss, and that the exceptions are the reason anyone checks.
Reference upper limits around forty units per litre for ALT are conventional rather than physiological; several groups have argued for limits closer to thirty for men and twenty-five for women.
Read the pattern before the magnitude, and the magnitude in multiples of the upper limit.
Answering this needs the magnitude in multiples of the upper reference limit, because the thresholds that matter clinically are defined that way and not in absolute units.
An isolated result three weeks after starting anything is difficult to interpret. A baseline taken before starting makes the same result trivially interpretable, which is the argument for baselines.
Isolated mild elevation is common and usually improves with weight loss.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.