Liver Tests AST and ALT and GGT Markers
How To Interpret Your Liver Function Tests ALT, AST, ALP.
Note: I am NOT your Dr….
Exercise, supplements, medications and drugs can all cause elevations of enzymes that are commonly included in liver function testing – alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP).
But how do you distinguish pathological elevations vs. those caused by intense exercise ?
ALT and AST are also known as aminotransferases or transaminases. They are considered good markers of liver inflammation that may impair its function. ALT is regarded as a reliable marker of liver damage or liver disease.
The name “liver function testing” is, however, somewhat of a misnomer; these tests are neither specific to the liver – the enzymes are also present in other tissues, e.g. AST is present in a far greater amounts in muscle than the liver – nor true measures of liver function.
Rather than assessing functions of the liver, the release of ALT and ALP (and AST to a much lesser extent) from liver cells to the bloodstream indicates liver cell damage or death, and/or blockage or damage in the biliary system if ALP and bilirubin are elevated).
As such the term “liver injury tests” would be more appropriate.
How high are elevations in ALT and AST are acceptable ?
Even though there is no universal agreement on what constitutes mild, moderate or marked aminotransferase elevation, a general clinical practice guideline is:
– Mild elevation = less than 5 times the upper reference limit.
– Moderate elevation = 5–10 times the upper reference limit.
– Marked elevation = over 10 times the upper reference limit.
Now, let’s compare this to commonly encountered elevations in aminotransferases – and other labs – caused by intense exercise…
Weightlifting results in profound increases in liver related parameters; these elevations can be prolonged, lasting for 1 week after performing an intense weightlifting workout.
Elevations in these enzymes are proportional to body weight, exercise type and exercise intensity. Anabolic steroid use will result in the highest enzyme levels, but steroid-free natural bodybuilders will also have significantly elevated levels of AST.
For drug-induced liver injury, the ALT cut off point of 5-fold over the upper end of the normal range (or 3-fold if total bilirubin exceeds its normal range by 2-fold).
The question becomes then how do you know if enzyme elevations are a harmless response to exercise, or an indication of liver damage ?
The simplest blood test that should be included when examining liver health in people engaging in regular intense resistance exercise is GGT (gamma-glutamyltranspeptidase).
The reason is that GGT distinguishes healthy people with resistance training induced elevations in ALT and AST from patients with hepatitis.
One notable study ( see ref below ) found that bodybuilders (both anabolic steroid non-users and users) both had a GGT level around 30 U/L (normal range for this assay; 8-78 U/L), while hepatitis patients had GGT levels of 212 U/L (i.e. a 2.7-fold elevation above the upper end of normal range).
This was confirmed in another study which showed that resistance exercise can cause highly pathological liver function tests in healthy men; while ALT, AST and CK were greatly elevated, GGT was not.
Therefore including GGT in blood testing for evaluation of liver status will help differentiation between transaminase elevations due to muscle damage vs. liver damage.
While GGT is a simple parameter to measure, it is not included in routine clinical lab panels, and thus has to be specifically requested.
Many doctors, don’t know that intense exercise can cause highly pathological liver function/disease lab tests, and they often refer a perfectly healthy person who happens to be exercising – whose lifestyle history has not been taken – to a liver disease specialist.
An interesting survey assessed whether primary care physicians accurately can distinguish between blood aminotransferase elevations caused by intense resistance training and indicating muscle damage vs. elevation caused by drug use.
Surveys were sent to physicians listed as practicing family medicine or sports medicine in the yellow pages of seven metropolitan areas. Blood test results showed elevated aspartate AST, ALT and CK, but normal GGT. It was found that 56 percent failed to mention muscle damage as a potential diagnosis, despite the markedly elevated CK level of the patient. 63 percent indicated liver disease as their primary diagnosis despite normal GGT levels.
When in doubt, make sure your doctor checks your GGT level together with the transaminases (ALT and AST) and ALP that you get from the standard Comprehensive Metabolic Panel. Because GGT is not included in routine clinical lab panels, you have to specifically request it.
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