G6PD Test: Purpose, High/Low Levels, Symptoms, Normal Range & Complete Guide
Overview
The G6PD Test measures the amount or activity of the enzyme Glucose-6-Phosphate Dehydrogenase in red blood cells. This enzyme plays an essential role in protecting red blood cells from oxidative stress. When a person with low G6PD levels is exposed to infections, certain medications, or specific foods such as fava beans, their red blood cells can break down more quickly than normal. This condition is called hemolytic anemia, where red blood cells are destroyed faster than the body can replace them.
G6PD deficiency is an inherited condition that is far more common in males because the G6PD gene is located on the X chromosome. Early diagnosis is important because avoiding certain triggers can prevent life-threatening complications.
Where Is G6PD Produced in the Body?
G6PD is an enzyme produced inside red blood cells. Its production is controlled by the G6PD gene, which is located on the X chromosome.
Why males are more affected
- Males have one X chromosome → a single defective gene causes deficiency
- Females have two X chromosomes → they can be carriers, or mildly affected depending on which X chromosome is active
Main Functions and Importance of G6PD
G6PD is essential for maintaining strong, healthy red blood cells, especially during times of stress.
1. Protects Red Blood Cells from Oxidative Stress
Red blood cells are constantly exposed to harmful molecules called free radicals.
G6PD helps prevent damage by neutralizing these molecules. Without enough G6PD, red blood cells become fragile and break easily.
2. Helps Maintain NADPH Levels
NADPH is required for:
- Regenerating reduced glutathione
- Removing harmful oxidative substances
- Protecting red blood cell membranes
Low NADPH means red blood cells cannot protect themselves from damage.
3. Prevents Hemolysis
In G6PD deficiency, even a mild trigger can cause rapid red blood cell destruction, leading to:
- Sudden anemia
- Jaundice
- Dark urine
4. Important During High-Stress Conditions
G6PD becomes especially important when the body is under stress, such as:
- Fever
- Infections
- Certain medications
- Chemical exposure
- Eating fava beans
People with low levels are at greatest risk during these times.
Causes of Low / Deficient G6PD Levels
Low G6PD activity is the main abnormal finding, and it usually results from:
1. Genetic Mutation (Most Common Cause)
G6PD deficiency is almost always inherited. Certain variants are more severe and cause stronger reactions.
2. Infections
Viral or bacterial infections increase oxidative stress, which can trigger hemolysis in people with G6PD deficiency.
3. Medications
Some medicines can trigger hemolytic episodes, including:
- Primaquine and other antimalarials
- Sulfa drugs
- Certain antibiotics
- High-dose aspirin
- Nitrofurantoin
4. Fava Beans (Favism)
Fava beans contain chemicals that cause oxidative stress and can lead to severe hemolysis in affected individuals.
Symptoms of Low / Deficient G6PD Levels
Symptoms appear primarily during a hemolytic episode, not when the person is stable.
1. Jaundice
Yellowing of the skin and eyes due to increased bilirubin.
2. Fatigue and Weakness
Caused by a sudden drop in red blood cell count.
3. Dark-Colored Urine
This occurs when hemoglobin from broken red blood cells is released into urine.
4. Shortness of Breath
Due to reduced oxygen-carrying capacity.
5. Rapid Heart Rate
The heart beats faster to compensate for anemia.
6. Pale Skin
Another indicator of low red blood cell levels.
Causes of High G6PD Levels
High G6PD levels are uncommon and usually not harmful.
Possible causes include:
1. Young Red Blood Cells
Reticulocytes (young red blood cells) have higher G6PD activity.
After a hemolytic episode, the body releases more reticulocytes, giving a false-normal or high result.
2. Laboratory Variations
Some laboratory methods may show higher activity due to test sensitivity.
3. Rare Genetic Variants
Certain rare variants may naturally have higher enzyme activity.
Symptoms of High G6PD Levels
High G6PD levels themselves do not cause symptoms.
However, elevated levels may indicate:
- Recovery from a hemolytic episode
- Increased production of new red blood cells
Reference Ranges
Ranges vary by laboratory, but typical values include:
| Result | Interpretation |
|---|---|
| 5.5 – 20.5 U/g Hb | Normal |
| Below reference range | Deficient (severity varies) |
Low G6PD activity confirms G6PD deficiency.
Sample Type
The test requires a:
- Blood sample
- Collected in an EDTA (purple-top) tube
This helps measure enzyme activity accurately.
Test Preparation
- No fasting required
- Avoid testing during or immediately after a hemolytic episode because reticulocytes can produce false-normal results
- Inform your doctor about:
- Medications
- Recent infections
- Family history of G6PD deficiency
When to Consult a Doctor
Seek medical attention if you experience:
Signs of Hemolysis
- Persistent tiredness
- Pale or yellow skin
- Dark urine
- Fast heartbeat
- Breathlessness
Exposure to Known Triggers
- Fava beans
- High-risk medications
- Chemical exposure
In Infants
Babies with unexplained or prolonged jaundice should be tested for G6PD deficiency.
Early diagnosis helps prevent severe complications and guides safe medication use.
Important Word Explanations
Enzyme Deficiency: Low levels or reduced activity of an enzyme
Hemolysis: Breakdown of red blood cells
Oxidative Stress: Damage caused by free radicals
NADPH: Molecule that protects red blood cells from oxidative damage
Favism: Hemolysis triggered by eating fava beans
Reticulocytes: Young red blood cells with higher G6PD activity
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