Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency is a genetic condition where red blood cells lack sufficient amounts of an enzyme that protects them from damage. Testing for G6PD deficiency is important for diagnosis and management, helping prevent complications.
Understanding G6PD Deficiency
G6PD is an enzyme present in all body cells, protecting red blood cells from oxidative stress. It helps produce NADPH, which neutralizes harmful reactive oxygen species within these cells. Without enough G6PD, red blood cells are vulnerable to damage from certain substances or situations.
When red blood cells are damaged due to G6PD deficiency, they break down prematurely, a process called hemolysis. This can lead to hemolytic anemia, a condition where red blood cells are destroyed faster than the body can replace them. Triggers for hemolysis in G6PD deficient individuals include infections, certain medications (like some antimalarials and sulfa drugs), and fava beans.
Reasons for G6PD Testing
Testing for G6PD deficiency identifies individuals at risk or diagnoses the condition. Newborn screening is common in many areas, especially where G6PD deficiency is prevalent, to detect it early. Some U.S. states include G6PD testing in their routine newborn screening panels.
Testing is also ordered for individuals experiencing unexplained hemolytic anemia, characterized by symptoms such as fatigue, pale skin, jaundice, dark urine, and a rapid heart rate. These symptoms suggest red blood cells are being destroyed faster than normal, prompting investigation. A known family history of G6PD deficiency also warrants testing, as the condition is inherited. In high-prevalence regions, healthcare providers may recommend testing before prescribing medications known to induce hemolysis.
Methods of G6PD Testing
Several laboratory methods test for G6PD deficiency, typically using a blood sample. The Fluorescent Spot Test (FST) is a common qualitative screening method that detects reduced G6PD activity. This test is simple, inexpensive, and provides visual results within minutes by observing blood spot fluorescence under ultraviolet light. A normal sample fluoresces brightly, while a deficient sample shows little to no fluorescence.
For precise measurement of G6PD enzyme activity, a quantitative spectrophotometric assay is the definitive test. This method measures the exact amount of G6PD enzyme activity in red blood cells, providing a numerical value to assess deficiency severity. Molecular genetic testing can also identify specific gene mutations responsible for G6PD deficiency, which is helpful for confirming a diagnosis, determining carrier status, and for family studies. G6PD enzyme activity tests should ideally be performed when the patient is not experiencing an acute hemolytic crisis, as newly formed red blood cells have higher enzyme levels and can lead to falsely normal results.
Interpreting G6PD Test Results
Interpreting G6PD test results involves understanding enzyme activity levels and the patient’s clinical background. Normal results indicate sufficient G6PD activity, suggesting deficiency is unlikely. For adults, a normal G6PD range is typically 5.5 to 20.5 units per gram of hemoglobin, though reference ranges vary by laboratory.
Deficient results, characterized by low G6PD activity, confirm the diagnosis, with the degree of deficiency varying. Severe deficiency (less than 10% of normal activity) can lead to chronic hemolytic anemia, while moderate deficiency (10% to 60% of normal activity) may cause intermittent hemolytic anemia linked to triggers. Females can be carriers, possessing one deficient gene and one normal gene; they may have intermediate enzyme levels, often remain asymptomatic, but can pass the gene to their children. A healthcare professional must interpret results, considering symptoms, medical history, and ethnic background, as G6PD deficiency is more common in people of African, Mediterranean, or Asian descent. A positive diagnosis leads to recommendations for avoiding known triggers and careful medication management to prevent hemolytic episodes.