When we receive a blood test, we see “SGPT” on one line and “ALAT” on another, and we wonder if the laboratory has measured two different things. In practice, SGPT and ALAT refer to exactly the same enzyme, alanine aminotransferase. The confusion arises from a change in nomenclature that not all laboratories have adopted at the same pace.
SGPT and ALAT: one enzyme, two nomenclatures
SGPT stands for Serum Glutamic Pyruvic Transaminase. This is the old English name used for decades in liver function tests. ALAT, for alanine aminotransferase, is the term adopted by the current international nomenclature.
Both acronyms refer to the same measurement, the same analytical technique, and the same result in international units per liter. When trying to understand the differences between ALAT and SGPT transaminases, we find that there are simply none on a biological level.
Some laboratories still display “SGPT” out of habit or because their software has not been updated. Others use “ALAT/SGPT” in tandem to avoid any confusion for the patient. A result labeled SGPT is read exactly like an ALAT result.
ALAT and ASAT: two hepatic enzymes not to be confused
The real clinical distinction is not between ALAT and SGPT, but between ALAT and ASAT (aspartate aminotransferase, formerly SGOT). These two enzymes circulate in low quantities in the blood when everything is fine. Their elevation signals cellular distress, but not necessarily in the same location.
ALAT is primarily concentrated in liver cells. When the level rises, liver damage is suspected first: steatosis, viral hepatitis, drug toxicity.
ASAT, on the other hand, is found in the liver but also in the heart, skeletal muscles, and red blood cells. An isolated elevation of ASAT may indicate a muscular or cardiac cause rather than a hepatic one.
The ratio between the two enzymes provides indications to the general practitioner. A significantly higher ALAT than ASAT points to a pure hepatic cause. The opposite may suggest muscle damage, excessive alcohol consumption, or hemolysis.
Reference thresholds for transaminases: the pitfalls of blood tests
It is often believed that a “normal” result from the laboratory is enough to rule out a problem. This is a too hasty reading. Reference ranges vary from one laboratory to another, and some are broader than what is recommended by scientific societies.
The American College of Gastroenterology sets lower upper limits than many city laboratories:
- In women, a threshold around 19 to 25 UI/L is considered the relevant upper limit, while some labs display norms well beyond that.
- In men, the recommended limit is between 29 and 33 UI/L, compared to sometimes higher ceilings in current reports.
- In newborns and children, physiological values are naturally higher and should not be compared to adult norms.
A “normal” ALAT level on paper can mask early fibrosis, especially in individuals with type 2 diabetes or abdominal obesity. The European recommendations of 2024 suggest searching for fibrosis using non-invasive tools like the FIB-4 score, and possibly elastography.
Elevated transaminases without liver disease: extra-hepatic causes
Before concluding a liver disease, the doctor must rule out several situations that elevate transaminases without involving the liver. These factors are often underestimated.
Intense physical exercise, particularly weight training, can temporarily increase ALAT and ASAT. Damaged muscle fibers release these enzymes into the blood. A measurement taken the day after a heavy session can yield a falsely alarming result.
Some common medications (statins, prolonged therapeutic doses of paracetamol, anti-inflammatories) cause a moderate elevation. The intake of dietary supplements, especially those containing hepatotoxic plants, is a frequent trap that the general practitioner should look for during questioning.
Hemolysis (destruction of red blood cells during collection or in the body) also skews the result, especially for ASAT. A poorly transported tube or a difficult draw can be enough to artificially inflate the level.
When transaminase measurement justifies further tests
A moderately elevated level (two to three times the upper limit) observed once does not necessarily trigger a thorough evaluation. The doctor usually requests a follow-up after ruling out transient causes.
The situation changes when the elevation persists over two measurements spaced a few weeks apart, or when it significantly exceeds normal levels. We then move on to targeted exploration:
- Serologies for viral hepatitis B and C to rule out chronic infection.
- Liver ultrasound to look for steatosis or structural abnormalities in the liver.
- FIB-4 score and, if necessary, elastography to assess the degree of fibrosis without biopsy.
- Iron studies (iron, ferritin) if hemochromatosis is suspected.
Isolated transaminase measurement is never enough to make a diagnosis. It guides the investigation, but it is the combination with clinical examination, imaging, and other markers that allows for a conclusion.
Remembering that SGPT and ALAT refer to the same enzyme already avoids a frequent source of unnecessary concern when reading a report. The clinically significant distinction is between ALAT and ASAT, as it points to different organs. And a result within the laboratory norms does not exempt from further evaluation if the metabolic context justifies it.
