From the Guidelines
G6PD deficiency is diagnosed through a blood test that measures the activity of the glucose-6-phosphate dehydrogenase enzyme in red blood cells, with the most common screening test being the fluorescent spot test, and for more definitive diagnosis, quantitative spectrophotometric analysis measures the exact enzyme activity level. The diagnostic tests for Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency include:
- Fluorescent spot test: a drop of blood is placed on filter paper and exposed to UV light, where normal samples will fluoresce brightly while deficient samples show reduced or no fluorescence
- Quantitative spectrophotometric analysis: measures the exact enzyme activity level for a more definitive diagnosis Testing is recommended for individuals with unexplained hemolytic anemia, those with a family history of G6PD deficiency, or before prescribing medications known to trigger hemolysis in deficient individuals, such as certain antimalarials, antibiotics, and NSAIDs 1, 2. It is essential to test for G6PD deficiency before administering certain medications, such as methylene blue, as it can worsen hemolysis in patients with G6PD deficiency 3. The test is crucial because G6PD deficiency affects approximately 400 million people worldwide and can cause severe hemolytic anemia when exposed to certain medications, foods, or infections 4. Early identification allows for prevention of hemolytic crises through avoidance of triggering factors. In cases where methemoglobinemia is suspected, it is essential to search for a history of G6PD deficiency, as methylene blue cannot be used in patients with G6PD deficiency 5. However, there is no sufficient evidence to recommend routine functional assay for G6PD activity in such cases. In real-life clinical practice, it is crucial to prioritize testing for G6PD deficiency to prevent severe hemolytic anemia and improve patient outcomes.
From the Research
Diagnostic Tests for G6PD Deficiency
The following diagnostic tests are used to detect Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency:
- Quantitative tests, such as measuring G6PD activity in whole blood or dried blood spots, which provide a direct measurement of enzyme activity 6, 7, 8
- Qualitative tests, including the fluorescent spot test (FST) and rapid diagnostic tests (RDTs), which provide a quick and simple way to detect G6PD deficiency 9, 10
- Spectrophotometry, which is considered the gold standard for measuring G6PD activity 9
- Colorimetric method, which can be used to measure G6PD activity in whole blood and dried blood spots 8
- Kinetic method, which can be used to measure G6PD activity in cord blood samples 10
Comparison of Diagnostic Tests
Studies have compared the performance of different diagnostic tests for G6PD deficiency, including:
- A comparison of FST and RDT against spectrophotometry, which found that FST and RDT performed well at a 30% cut-off activity, but had varying sensitivity and specificity in different populations 9
- A comparison of quantitative and qualitative tests, which found that quantitative tests provided a more accurate measurement of G6PD activity, but qualitative tests were simpler and faster to perform 10
Sample Collection and Analysis
Different samples can be used for G6PD deficiency testing, including: