Liver Function Tests: What ALT and AST Really Tell You

Your liver is the largest internal organ in your body, and it does more than most people realize. It filters toxins from your blood, metabolizes medications, produces bile for digestion, stores glycogen for energy, makes proteins your blood needs to clot, and processes almost everything you eat or drink. When liver cells are damaged — by any cause — they release enzymes into the bloodstream, and that's what your liver function tests measure.

Understanding what these tests mean is particularly important if you take medications, drink alcohol, or are being evaluated for new treatments.

The Key Liver Enzymes

ALT (Alanine Aminotransferase)

Normal range: Approximately 7 to 56 U/L

ALT is found primarily in the liver. This makes it the most specific marker for liver cell damage. When you see an elevated ALT, the problem is almost always hepatic (liver-related).

ALT is the enzyme your doctor watches most closely for medication-related liver injury.

AST (Aspartate Aminotransferase)

Normal range: Approximately 10 to 40 U/L

AST is found in the liver but also in the heart, skeletal muscles, kidneys, brain, and red blood cells. This means an elevated AST doesn't necessarily point to the liver — it could come from a recent intense workout, muscle injury, or even a heart problem.

When both ALT and AST are elevated, the liver is the likely source. When AST is elevated alone with normal ALT, your doctor will consider non-liver causes.

The AST/ALT Ratio

The relationship between AST and ALT helps narrow down the cause:

• ALT higher than AST: Typical of non-alcoholic fatty liver disease, viral hepatitis, and most medication-related injury
• AST higher than ALT (ratio greater than 2:1): Suggests alcoholic liver disease
• Both massively elevated (10-100x normal): Suggests acute hepatitis, toxin exposure, or ischemic liver injury

ALP (Alkaline Phosphatase)

Normal range: Approximately 44 to 147 U/L

ALP is found in the liver and bones. Elevated ALP with elevated ALT/AST points toward the liver — specifically bile duct or cholestatic (blockage-related) problems. Elevated ALP alone might be bone-related, particularly in growing adolescents, pregnant women, or people with bone disorders like Paget's disease.

GGT (Gamma-Glutamyl Transferase)

Normal range: Approximately 9 to 48 U/L

GGT helps distinguish whether elevated ALP is coming from the liver or bones. It's also sensitive to alcohol use — even moderate drinking can elevate GGT. Some doctors use it as a marker for recent alcohol consumption.

Bilirubin

Normal range: 0.1 to 1.2 mg/dL (total)

Bilirubin is the yellow pigment produced when old red blood cells are broken down. Your liver processes bilirubin and excretes it in bile. Elevated bilirubin causes jaundice — the yellowing of skin and eyes.

Mild elevations (up to about 2-3 mg/dL) are often due to Gilbert's syndrome, a benign genetic condition affecting about 5-10% of the population. Higher elevations suggest liver disease, bile duct obstruction, or excessive red blood cell destruction.

Common Causes of Elevated Liver Enzymes

Non-Alcoholic Fatty Liver Disease (NAFLD)

This is the most common cause of mildly elevated liver enzymes in primary care. It affects roughly 25% of adults and is strongly associated with obesity, insulin resistance, and metabolic syndrome. The liver accumulates fat, which causes inflammation and enzyme elevation.

In most cases, ALT is mildly elevated (1.5 to 3 times normal) and AST is normal or slightly elevated. Weight loss of 7-10% of body weight can significantly improve or normalize liver enzymes in NAFLD.

Alcohol

Regular or heavy alcohol use is a well-known cause of liver enzyme elevation. The pattern often shows AST higher than ALT with elevated GGT. Even "moderate" drinking can cause enzyme bumps in some individuals.

Medications

Many common medications can stress the liver:

• Acetaminophen (Tylenol): The most common cause of acute liver failure in the US, usually from overdose or combining with alcohol
• Statins: Can cause mild enzyme elevation in 1-3% of patients; significant liver injury is rare
• NSAIDs: Ibuprofen, naproxen — uncommon but possible liver effects with regular use
• Antibiotics: Amoxicillin-clavulanate, fluoroquinolones, and isoniazid are known hepatotoxins
• Finasteride: Generally safe for the liver, but baseline and periodic monitoring is prudent
• Testosterone: Oral forms (less commonly used) carry more liver risk than injectable or topical forms
• Herbal supplements: Kava, green tea extract in high doses, and many "liver detox" supplements can ironically damage the liver

This is exactly why we check liver function before starting medications and monitor periodically. Catching a medication-related enzyme bump early allows us to adjust before any real damage occurs.

Viral Hepatitis

Hepatitis B and C are significant causes of chronic liver enzyme elevation. Hepatitis B is screened for with surface antigen testing; hepatitis C with an antibody test. Both are treatable — hepatitis C is now curable in most cases.

Other Causes

• Autoimmune hepatitis
• Hemochromatosis (iron overload)
• Wilson's disease (copper overload)
• Celiac disease (surprisingly, can present with elevated liver enzymes)
• Thyroid disorders
• Heart failure (liver congestion)
• Recent vigorous exercise (can elevate AST from muscle, not liver)

When to Worry

Mild elevation (1-3 times normal): Common, often benign, but warrants investigation if persistent. Your doctor will likely repeat the test in 4-6 weeks and look for causes.

Moderate elevation (3-10 times normal): Needs evaluation — imaging (ultrasound), additional blood work, and possibly referral to a specialist.

Severe elevation (greater than 10 times normal): This is urgent. Causes include acute viral hepatitis, toxin exposure (including acetaminophen overdose), ischemic hepatitis (from low blood flow to the liver), and autoimmune hepatitis.

One key point: the degree of enzyme elevation doesn't always correlate with the severity of liver disease. Some patients with cirrhosis (advanced scarring) have only mildly elevated enzymes or even normal ones. Others with a temporary viral illness have sky-high numbers that resolve completely.

Liver Function in Men's Health

For men's health patients specifically, liver function testing is relevant in several ways:

• Before starting finasteride or dutasteride: While these medications are generally liver-safe, baseline liver function ensures we have a reference point
• During TRT monitoring: Testosterone is metabolized by the liver; we check enzymes periodically to confirm safe processing
• Alcohol habits: Many men's health conversations include discussions about alcohol use, and liver enzymes provide objective data
• Supplement use: Men frequently take multiple supplements (protein powders, pre-workouts, testosterone "boosters") — some of which stress the liver

How Coral Monitors Your Liver

At Coral, liver function tests are part of our standard baseline labs. We check them before starting any medication that's metabolized by the liver, and we recheck them periodically during treatment.

We don't just look at the numbers in isolation — we consider your medications, supplements, alcohol use, body weight, and the trend of your results over time. If something looks off, we investigate the cause before it becomes a problem.

If you're starting a new medication or just want to know how your liver is doing, start your visit with Coral and get labs that are actually explained to you.

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