Gamma-GT

Gamma-GT, gamma-glutamyltransferase, sits in the wall of the bile ducts and in the liver cells, where it helps recycle glutathione, the cell's main protector against oxidative damage. If those cells become irritated, it leaks into your blood. It responds to everything that burdens the liver, and earlier than ALT: with regular alcohol, with fat in the liver, with medicines the liver has to break down, and with a bile drainage that does not flow well. That sensitivity is also the limitation. A high gamma-GT says your liver or bile ducts are burdened, not by what, and the pattern with the other values points the way. High gamma-GT with high ALT is the liver; high gamma-GT with high ALP and bilirubin is the bile ducts; high gamma-GT with a normal ALT and an AST that rises more than ALT is alcohol; and high ALP with a normal gamma-GT is not liver but bone, because gamma-GT does not rise from bone problems. Your report shows gamma-GT in U/L. Normal is up to about 55 U/L for a man from age 19 and up to 38 U/L for a woman, and here the labs agree. A healthy liver sits well below that. The enzyme has a half-life of ten days or so, so a change in what you drink or take shows after a few weeks.

Gamma-GT is the most honest measure of what alcohol does to your liver. Alcohol switches on the production of the enzyme in the liver cells, and in anyone who drinks regularly the value sits high while ALT can still be normal. It does not respond to a single evening, but to the average of the last few weeks. That makes it the value that shows what a dry January or a month without delivers: in most people gamma-GT falls back to normal in four to six weeks, and that is a concrete result of a concrete decision. The second reason is that gamma-GT moves with the whole metabolic picture. Belly fat, insulin resistance, high triglycerides and fatty liver lift it, and a gamma-GT at the top of the band goes together with a higher risk of diabetes and cardiovascular disease, even within the normal band. The enzyme is a measure of oxidative stress, and it falls with weight loss, exercise and less sugar just as well as with less alcohol. The third reason is the bile drainage. Gallstones, a narrowing or an inflammation of the bile ducts let gamma-GT and ALP rise together, often with bilirubin alongside and complaints in the upper right of the abdomen. That is a different picture from liver strain, and the combination of gamma-GT and ALP tells the two apart without further investigation.

A high gamma-GT means liver or bile ducts under strain. In order of how often it occurs: alcohol, fatty liver, medicines, a congested bile drainage, and rarely heart failure, in which the liver sits full of blood through congestion. ALT and ALP point the way: high ALT alongside is the liver, high ALP alongside is the bile ducts, only gamma-GT high is usually alcohol or medicines. A slightly raised value with otherwise normal liver values is almost always lifestyle and falls within weeks. A low gamma-GT means nothing; it is not a deficiency and a low value is favourable rather than unfavourable. Always read gamma-GT beside ALT, AST, ALP and bilirubin, and with a rise beside your triglycerides and waist. Better to have blood drawn in an ordinary week than after a party weekend, unless you want to see exactly what that does.