What is the Difference Between ALT and ALP

ALT and ALP are two very important liver enzymes. Liver enzymes are proteins that speed up chemical reactions in the body. Some of these chemical reactions are producing bile, producing substances that help blood clot, breaking down proteins and toxins, and fighting infections. Both ALT and ALP help break down proteins. These enzymes are also diagnostic markers of different diseases, such as pancreatitis and biliary obstruction.

The key difference between ALT and ALP is their location. ALT is an enzyme mainly present in the liver, while ALP is an enzyme found in many body parts.

CONTENTS

1. Overview and Key Difference
2. What is ALT  
3. What is ALP
4. Similarities – ALT and ALP
5. ALT vs ALP in Tabular Form
6. Summary – ALT vs ALP
7. FAQ: ALT and ALP

What is ALT?

Alanine transaminase (ALT) is a liver enzyme discovered in the mid-1950s by Arthur Karmen and colleagues. It is found in plasma and other tissues in the body, as well. This enzyme helps in converting alanine into pyruvate through the transferring of an amino group from L-alanine to α-ketoglutarate. This enzyme is routinely measured as a biomarker for liver health.

Figure 01: ALT

The half-life of ALT in the circulation approximates 47 hours. After 47 hours, this enzyme is cleared from sinusoidal cells in the liver. Furthermore, elevated levels of ALT may often suggest medical problems like viral hepatitis, diabetes, congestive heart failure, and liver damage.

What is ALP?

Alkaline phosphatase (ALP) is an enzyme present in nearly all tissues. But it is mainly found in the bone and liver. It can also be found in the bile duct, bones, kidneys, intestine, and placenta in pregnant people. The physiological role of this enzyme is dephosphorylating compounds.

Figure 02: ALP

The normal ALP reference range is from 44 to 147 international units per liter (IU/L). ALP in the blood is measured by two tests: comprehensive metabolic panel (CMP) and liver panel. High ALP levels in the blood may indicate that there is damage to the liver or that the person has a type of bone disorder

Similarities Between ALT and ALP

1. ALT and ALP are two liver enzymes.
2. Both enzymes are present in plasma and other body tissues.
3. Both enzymes help in breaking down the protein.
4. They are used as diagnostic biomarkers for diseases in laboratories.

Difference Between ALT and ALP

Definition

1. ALT is a liver enzyme that catalyzes the transfer of an amino group from L-alanine to α-ketoglutarate.
2. ALP is a liver enzyme that catalyzes the physiological reactions of dephosphorylating compounds.

Molecular Weight

1. ALT has a molecular weight is 93.5 kDa.
2. ALP has a molecular weight is 86 kDa.

Normal Concentration in the Blood

1. The normal range of ALT is 4 to 36 U/L.
2. The normal range of ALP is 44 to 147 IU/L.

Normal Function

1. ALT transfers an amino group from L-alanine to α-ketoglutarate.
2. ALP dephosphorylates compounds.

As a Diagnostic Marker for Diseases

1. ALT is used as diagnostic markers for viral hepatitis, diabetes, congestive heart failure, liver damage, bile duct problems, infectious mononucleosis, or myopathy.
2. ALP is used as diagnostic markers for Liver and bone disorders.

Summary – ALT vs ALP

ALT is mainly found in liver, bones, kidneys, and digestive system while ALP is mainly found in liver, bile duct, bones, kidneys, intestine and placenta in pregnant people. Furthermore, ALT responsible for converting alanine into pyruvate through the transferring of an amino group from L-alanine to α-ketoglutarate and forming glutamate and pyruvate whereas ALP is responsible for metabolizing organic phosphate esters. This summarizes the difference between ALT and ALP.

FAQ: ALT and ALP

1. What are the symptoms of a weak liver?

• The early symptoms of a weak liver include feeling frequently unwell and tired all the time, loss of weight and muscle, loss of appetite, nausea, tenderness in the liver area, spider-like small blood capillaries noticeable on the skin (above waist level), and disturbed sleep patterns.

2. What are the 4 liver enzymes?

• The four common liver enzymes include alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and gamma-glutamyl transferase (GGT).

3. What is a high ALT level?

• In an ALT test result, ALT should be in the range of  4 to 36 U/L.. Higher than this concentration is a clear indicator of serious liver disease, but a mildly elevated ALT result is often ascribed to the use of medication such as statins, alcohol, or obesity.

4. What does ALP do in the liver?

• ALP is an enzyme found in the highest concentration in the liver and bone. It is important for breaking down proteins. Higher than usual levels of ALP in the blood may mean liver damage, such as a blocked bile duct, or certain bone diseases.

5. Does high ALP mean fatty liver?

• Alkaline phosphatase can be elevated in fatty liver disease. But it is more common for enzymes AST and ALT to be elevated in the fatty liver disease. An ultrasound scan is a good option for proper diagnosis of fatty liver with ALP test.

Reference:

1. Marc S Orlewicz, MD. “Alanine Aminotransferase.” Reference Range, Interpretations, Collection and Panels, Medscape.
2. Lowe, Dhruv. “Alkaline Phosphatase.” StatPearls. U.S. National Library of Medicine.

Image Courtesy:

1. “Alanine transaminase reaction” By Akane700 – Own work (CC BY-SA 3.0) via Commons Wikimedia

2. “Alkaline phosphatase – 2” By Madhero88 at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia

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