What is the Alkaline Phosphatase Isoenzymes Test?

The Alkaline Phosphatase (ALP) Isoenzymes test measures and separates different forms of alkaline phosphatase produced by specific tissues in the body. While a standard ALP test shows whether levels are high or low, isoenzyme analysis identifies where the enzyme is coming from, most commonly the liver, bones, intestines or placenta.

Alkaline phosphatase is present throughout the body, but elevations can have very different clinical meanings depending on the source. Isoenzyme testing is used when total ALP is raised or unexplained, allowing clinicians to determine whether the elevation reflects liver disease, bone turnover, metabolic bone disorders or other conditions.

This test is particularly valuable when symptoms are non-specific or when standard liver or bone tests do not provide a clear explanation.

Why do I need a test for Alkaline Phosphatase Isoenzymes?

You may need this test if your alkaline phosphatase level is elevated and the cause is unclear. Total ALP alone cannot differentiate between liver-related conditions and bone disorders, which can lead to unnecessary investigations or delayed diagnosis.

Isoenzyme testing helps target further investigations accurately. For example, identifying a liver-derived ALP elevation may prompt imaging of the biliary system, while a bone-derived elevation may indicate increased bone turnover, healing fractures or metabolic bone disease.

Symptoms and scenarios where testing is recommended:

• Persistently raised alkaline phosphatase
• Unexplained abnormal liver function tests
• Bone pain or bone deformities
• Suspected metabolic bone disease
• Monitoring known liver or bone conditions
• Suspected biliary obstruction
• Paget’s disease suspicion
• Healing fractures with abnormal blood results
• Differentiating liver vs bone causes of symptoms

Benefits of the Alkaline Phosphatase Isoenzymes Test

·      Identifies the tissue source of raised ALP
Distinguishes whether elevated ALP originates from liver, bone or other tissues.

·      Prevents unnecessary investigations
Helps clinicians focus imaging and follow-up on the correct organ system.

·      Clarifies ambiguous liver function results
Especially useful when ALT, AST or GGT are inconclusive.

·      Supports diagnosis of bone metabolism disorders
Elevated bone isoenzymes may indicate Paget’s disease, osteomalacia or high bone turnover.

·      Aids assessment of biliary and cholestatic disease
Liver-derived isoenzymes often rise in bile duct obstruction or cholestasis.

·      Useful in monitoring known conditions
Tracks disease progression or treatment response in liver and bone disorders.

·      Improves diagnostic accuracy
Adds specificity beyond standard ALP testing alone.

·      Provides actionable clinical insight
Results guide targeted referrals, imaging and management decisions.

Step-by-Step: How Testing Works

Choose your preferred testing method

You can attend one of our UK partner clinics or arrange a home or hotel visit with a mobile phlebotomist.

Option 1 – In-Clinic Blood Draw

1. Choose your nearest UK clinic and book an appointment.
2. A clinician or phlebotomist collects a venous blood sample.
3. The sample is analysed to separate ALP isoenzymes.
4. Results are delivered securely online.

Option 2 – Home or Hotel Phlebotomy (+£60)

1. Book a UK-wide home or hotel visit at a time that suits you.
2. A trained phlebotomist collects your blood sample on-site.
3. The sample is packaged and sent to the laboratory.
4. Results are uploaded digitally without travel.

Access your report

You can download your report and share it with your GP, hepatologist or endocrinologist as needed.

Your Results Explained

Low Levels

Low total ALP or low isoenzyme activity may be seen in malnutrition, zinc deficiency, hypothyroidism or rare genetic conditions.
Typical UK reference (total ALP): ~30–130 IU/L (varies by lab and age).
Low bone isoenzyme activity may suggest reduced bone turnover.

Normal Levels

Normal isoenzyme distribution indicates balanced liver and bone activity.
This suggests that ALP production is within expected limits and no significant liver or bone pathology is present.

High Levels

• Liver isoenzyme elevated: suggests cholestasis, bile duct obstruction, liver disease or infiltrative liver disorders.
• Bone isoenzyme elevated: associated with increased bone turnover, Paget’s disease, healing fractures or vitamin D deficiency.
• Mixed elevation: may indicate combined liver and bone involvement and requires further evaluation.