Monoamine Oxidase

Monoamine Oxidase (MAO) is a mitochondrial enzyme that catalyzes the oxidative deamination of monoamines such as:

• Dopamine
• Norepinephrine
• Serotonin
• Tyramine

There are two types:

• MAO-A
• MAO-B

In clinical biochemistry, serum MAO activity was historically used as a marker of liver fibrosis.

1️⃣ Liver Disease (Most Important)

Serum MAO levels are increased in:

• Cirrhosis
• Chronic hepatitis
• Hepatic fibrosis

🔎 MAO levels correlate with degree of fibrosis, not acute liver cell damage.

👉 Hence, it was considered a marker of chronic liver disease progression.

2️⃣ Not Elevated in Acute Hepatitis

Unlike ALT and AST:

MAO does not significantly increase in acute hepatocellular injury.

It reflects chronic structural damage, especially fibrosis.

3️⃣ Limited Current Use

Now largely replaced by:

• Imaging studies
• Fibrosis markers
• Liver biopsy

Rarely used in routine liver function tests today.

4️⃣ Neurological Importance (Pharmacological Relevance)

Though not commonly measured clinically for diagnosis:

MAO inhibitors (MAOIs) are used in:

• Depression
• Parkinson’s disease

Inhibition of MAO increases neurotransmitter levels.

Normal Reference Range

Varies depending on method and lab; not commonly included in routine LFT panels.