Liver enzymes: what a raised ALT, AST or GGT usually means

The liver clears toxins, processes fats and sugars, makes proteins and stores energy. It is also very good at coping quietly, so a blood test is often the first sign that it is under strain. A liver panel is a set of enzymes and proteins that each tell a slightly different part of the story.

What each marker measures

• ALT is found mostly in liver cells. When liver cells are irritated or damaged, ALT leaks into the blood. It is the most liver specific enzyme on the panel.
• AST is found in the liver, but also in muscle and the heart. It rises with liver injury, and after hard exercise.
• GGT sits in the liver and bile ducts. It is sensitive to alcohol, some medicines and fatty liver.
• ALP comes from the bile ducts and from bone. It is naturally higher in teenagers who are still growing and in pregnancy.
• Bilirubin is a yellow pigment from the normal breakdown of red cells, which the liver clears.
• Albumin and total protein reflect how well the liver makes proteins, and also your nutrition and hydration.

The ALT limit LifePrint uses

Many labs print an upper limit for ALT of around 40 U/L. The American College of Gastroenterology 2017 guideline recommends lower limits for a truly healthy liver: 33 U/L for men and 25 U/L for women. LifePrint uses these stricter limits, because fatty liver can raise ALT into the 30s long before it crosses a lab's upper limit.

Results up to twice the ACG limit, so 33 to 66 U/L in men and 25 to 50 U/L in women, are shown in LifePrint's grey zone. The guideline advises repeating a mild rise before investigating, because many settle on their own. Higher results are graded by how many times above the limit they are, and very high results are marked as urgent.

Fatty liver: the most common cause

Fat building up in the liver is now the most common reason for raised liver enzymes. It is closely linked to carrying weight around the middle, insulin resistance, type 2 diabetes, high triglycerides and high blood pressure. Doctors now call it metabolic dysfunction associated steatotic liver disease, or MASLD, to reflect that link.

Fatty liver usually causes no symptoms. In most people it stays mild, but in some it leads to inflammation and scarring over many years. The encouraging part is that it responds well to change. Gradual weight loss, regular activity, less sugar and refined starch, and less alcohol can bring ALT back towards normal within months.

Alcohol

Alcohol raises GGT in many regular drinkers, sometimes even at levels people consider moderate. Heavier drinking can also raise AST, often more than ALT, and can enlarge red cells, which shows up as a high MCV on the blood count. GGT usually falls over several weeks after cutting down, which makes it a useful marker to repeat.

Medicines and supplements

Many medicines can nudge liver enzymes, and most of the time the effect is mild and harmless. Some need closer attention. Examples include:

• Cholesterol lowering statins, which commonly cause a small ALT rise that does not usually mean stopping them.
• Some antibiotics, including amoxicillin with clavulanic acid.
• TB treatment and some antiretroviral medicines, which your clinic will already be monitoring.
• Paracetamol taken above the recommended dose, or regularly with alcohol.
• Some seizure medicines, which commonly raise GGT.
• Anabolic steroids, and herbal or bodybuilding supplements, which are a frequently overlooked cause.

Do not stop a prescribed medicine because of a liver result without speaking to the doctor who prescribed it.

Other causes worth ruling out

If a raised ALT does not settle on a repeat test, a doctor will usually look for other causes. In South Africa that includes hepatitis B, which is common and often silent. Less common causes include hepatitis C, iron overload, thyroid problems, coeliac disease and autoimmune liver conditions. Your Essentials panel includes ferritin and TSH, which helps with some of these.

A mildly raised bilirubin

A slightly high bilirubin with otherwise normal liver tests is most often Gilbert's syndrome, a harmless inherited trait that affects a few people in every hundred. Bilirubin rises further when you fast or are unwell. LifePrint flags this pattern as likely Gilbert's rather than liver disease.