Aldolase (ALD)

Overview

Aldolase (ALD) is a cytoplasmic glycolytic enzyme found in the liver, skeletal muscles, and brain, as described in the document (page 2). It plays a central role in carbohydrate metabolism by catalyzing the reversible conversion of fructose-1,6-bisphosphate into dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate, a key step in glucose breakdown and energy production. The reaction illustration on page 3 visually demonstrates this biochemical conversion.

The document explains that aldolase is present in three isoenzymes—A, B, and C—each with unique tissue distribution (page 4).

1. Aldolase A is found in muscle and red blood cells.
2. Aldolase B is found in the liver, kidney, and small intestine.
3. Aldolase C is concentrated in the brain and neuronal tissue.

Although historically used to assess muscle damage, It has largely been replaced by CK, ALT, and AST because it is a nonspecific marker (page 2). However, it still assists in diagnosing muscular disorders, liver diseases, and hereditary fructose intolerance, and in monitoring disease progression.

Symptoms

This testing is ordered when symptoms indicate muscle injury, liver involvement, or metabolic abnormalities. The document’s indications table (page 7) helps identify the symptomatic scenarios associated with elevated ALD.

Muscle-Related Symptoms

Symptoms prompting testing include:

1. Muscle weakness
2. Muscle pain
3. Reduced mobility or fatigue
4. These may reflect muscular dystrophy, dermatomyositis, polymyositis, or myositis due to trauma or inflammation.

Liver-Related Symptoms

Because ALDB is present in the liver, symptoms related to hepatic disorders include:

1. Jaundice
2. Abdominal pain
3. Fatigue and malaise
4. These may occur in acute or toxic hepatitis.

Metabolic Symptoms

Hereditary fructose intolerance (page 15) can lead to:

1. Hypoglycemia
2. Gastrointestinal discomfort after fructose ingestion
3. Signs of toxic metabolite buildup

Advanced Muscle Disease Symptoms

Late-stage muscular dystrophy (page 14) may show:

1. Progressive muscle wasting
2. Loss of functional capacity

These symptoms guide clinicians to use these levels as part of a broader diagnostic assessment.

Causes

The document outlines biochemical and disease-related causes for abnormal levels.

Causes of Increased ALD

(Page 13 and page 16)

1. Muscle damage such as rhabdomyolysis
2. Muscular dystrophy
3. Dermatomyositis and polymyositis
4. Viral hepatitis
5. Heart disease
6. Megaloblastic and hemolytic anemia
7. Cancer, including prostate, lung, breast, and metastatic tumors

Elevations occur because damaged cells release aldolase into the bloodstream.

Causes of Decreased ALD

(Page 14–15)

1. Hereditary fructose intolerance (HFI): Defect in Aldolase B leads to fructose-1-phosphate buildup and impaired metabolism
2. Late-stage muscular dystrophy

These decreases reflect diminished enzyme production or impaired metabolic capacity.

Risk Factors

Risk factors correspond to conditions in which aldolase levels may become abnormal or when testing becomes clinically important. The document highlights several categories (pages 7, 13, 16):

1. Muscle Diseases

Individuals with:

1. Muscular dystrophy
2. Dermatomyositis
3. Polymyositis
4. Muscle injury or inflammation

2. Liver Disorders

Those with acute viral hepatitis, toxic liver injury, or cirrhosis may show abnormal levels.

3. Genetic Disorders

Patients with hereditary fructose intolerance have dysfunctional Aldolase B and are at risk of metabolic complications.

4. Hematologic Disorders

Megaloblastic anemia, hemolytic anemia, and leukemia may be associated with elevated aldolase.

5. Cancer

Higher enzyme expression is linked with tumor progression and metastasis.

6. Injections or Drug Exposure

Page 8 notes temporary increases in aldolase after intramuscular injections, exposure to chlorinated insecticides, or hepatotoxic medications.

Prevention

Prevention focuses on avoiding false elevations or reductions in aldolase testing and minimizing factors that influence enzyme activity.

1. Follow Sample Collection Precautions

(Page 8–9)

1. Maintain a 72-hour gap between intramuscular injections and blood collection.
2. Avoid hemolysis and exposure to chlorinated insecticides.
3. Stop hepatotoxic drugs 48 hours before sample collection.
4. Stop phenothiazine 48 hours beforehand to prevent artificially low levels.
5. Collect 3.0 mL of blood in a plain red-capped tube and separate serum early because aldolase activity decreases on storage.

2. Use Appropriate Testing Methods

(Page 10)

Methods include:

1. Quantitative enzymatic assays
2. Immunoassays
3. Chromatographic assays

3. Monitor Disease Progression

(Page 16)

Regular monitoring helps track therapy response in muscle disease, reducing complications from delayed diagnosis.

4. Manage Underlying Conditions Early

Addressing muscle, liver, and metabolic disorders reduces the risk of abnormal aldolase levels and prevents tissue injury.