G6PD (Glucose-6-Phosphate Dehydrogenase) EDTA Whole Blood

Diabetes

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Measures blood sugar levels to diagnose diabetes

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G6PD (Glucose-6-Phosphate Dehydrogenase) EDTA Whole Blood - Comprehensive Medical Test Guide

Section 1: Why is it done?
- Test Overview: The G6PD test measures the activity level of glucose-6-phosphate dehydrogenase, an enzyme that protects red blood cells from oxidative damage. This genetic test detects deficiencies in this enzyme, which can lead to hemolytic anemia when exposed to certain triggers.
- Primary Indications for Testing: Family history of G6PD deficiency; acute hemolytic anemia episode; jaundice in neonates or infants; recurrent or unexplained hemolytic episodes; ethnic background at higher risk (African, Mediterranean, Asian descent); before prescribing medications known to trigger G6PD hemolysis
- When This Test is Performed: During routine newborn screening programs; when evaluating hemolytic anemia; when assessing drug-induced hemolysis; during genetic counseling; before initiating potentially hemolytic medications; when investigating unexplained jaundice or pallor
- Clinical Significance: G6PD deficiency is the most common enzymopathy worldwide, affecting over 400 million people. It is an X-linked recessive genetic disorder with variable expression depending on the specific enzyme variant and environmental triggers.
Section 2: Normal Range
- Reference Values: Normal G6PD enzyme activity: 7.0-20.5 U/gHb (units per gram of hemoglobin) or 270-530 mU/10^12 RBCs depending on laboratory methodology
- Units of Measurement: U/gHb (International Units per gram of hemoglobin) or mU/10^12 RBCs (milliunits per 10 trillion red blood cells). Some labs may report as percentage of normal activity.
- Result Interpretation Categories: Normal (≥7.0 U/gHb): Full enzyme activity, no deficiency; Heterozygous carrier females (50-90% of normal): Intermediate activity, generally asymptomatic but may have mild hemolysis with triggers; Homozygous/hemizygous deficiency (<2.0 U/gHb): Severe deficiency with significant hemolysis risk
- Interpretation of Normal Values: Normal results indicate adequate G6PD enzyme activity and minimal risk of hemolytic episodes. Patient can safely receive medications that may trigger hemolysis in deficient individuals. No special precautions required for triggers like fava beans or infections.
- Interpretation of Abnormal Values: Low or absent enzyme activity indicates G6PD deficiency, requiring careful medication selection, avoidance of known triggers, and patient education about risk factors. Severity correlates with hemolysis risk.
Section 3: Interpretation
- Class I (Severe Deficiency - Activity <10% normal): Chronic hemolytic anemia with possible splenomegaly; high risk for severe hemolytic episodes (crises); triggered by infections, fava beans, certain medications, acidosis, or stress; may require transfusions; Mediterranean and Asian variants typically in this category
- Class II (Moderate Deficiency - Activity 10-50% normal): Hemolytic episodes typically occur only after exposure to triggers; may have baseline mild anemia; risk increases significantly with infections, drugs, or oxidative stress; African variant (A-) commonly in this class
- Class III (Mild Deficiency - Activity 50-90% normal): Heterozygous females primarily; generally asymptomatic unless exposed to significant oxidative stress; normal blood counts in steady state; may experience mild hemolysis with severe infections or high-dose medications
- Factors Affecting Test Results: Recent transfusion (false normal results); acute hemolytic episode (reticulocytosis may mask deficiency); age of red blood cells; laboratory methodology variation; specific enzyme variant; hemoglobin levels; concurrent illness or infection
- Clinical Significance of Different Patterns: Very low values: High risk for spontaneous hemolysis and need for preventive measures; Borderline low values: Requires lifestyle modification and medication avoidance; Normal values: Permits standard medical management without G6PD-related restrictions
- Gender Differences in Interpretation: Males: Hemizygous - either have normal or deficient enzyme with clear-cut results; Females: Heterozygous carriers may show intermediate values due to X-inactivation (lyonization), resulting in variable expression
Section 4: Associated Organs
- Primary Organ System Involved: Hematologic system (blood) - specifically red blood cells; G6PD enzyme located in RBC cytoplasm where it maintains antioxidant defenses via the pentose phosphate pathway
- Spleen Involvement: Splenomegaly common in Class I deficiency due to chronic hemolysis and RBC destruction; may develop splenic infarction during severe hemolytic crises; spleen becomes key filtering organ for damaged cells
- Liver Function: Elevated bilirubin from hemolysis may cause jaundice; risk of gallstones from chronic hemolysis; liver attempts to metabolize excess hemoglobin breakdown products; neonatal jaundice due to inadequate bilirubin conjugation combined with hemolysis
- Kidney/Renal System: Risk of acute kidney injury during severe hemolytic crises from myoglobinuria and tubular damage; chronic hemolysis may lead to secondary iron overload affecting renal function
- Conditions Associated with Abnormal Results: G6PD deficiency; acute hemolytic anemia; hemolytic disease of the newborn; neonatal jaundice; drug-induced hemolysis; infection-triggered hemolysis; fava bean-induced hemolysis (favism)
- Potential Complications of Abnormal Results: Severe hemolytic crisis requiring transfusion; acute kidney injury; jaundice and kernicterus (in neonates); splenic infarction; cholelithiasis from chronic hemolysis; iron overload from multiple transfusions; thrombosis risk during acute crises; growth delay in children with chronic hemolysis
- Medications That Trigger Hemolysis in G6PD Deficiency: Antimalarials (primaquine, pamaquine); sulfonamides; NSAIDs (aspirin in high doses); nitrofurantoin; dapsone; sulfa drugs; phenacetin; aspirin; sulfonylureas; certain antibiotics; antimycobacterials
- Other Triggering Factors: Fava beans and other legumes; bacterial infections (UTI, pneumonia, TB); viral infections (influenza, hepatitis); metabolic acidosis; hypoglycemia; severe exercise or stress; altitude exposure; mothballs (naphthalene)
Section 5: Follow-up Tests
- Initial Follow-up Tests if Deficiency Confirmed: Complete blood count (CBC) - assess hemoglobin, hematocrit, and reticulocyte count; Reticulocyte count - indicates bone marrow response to hemolysis; Peripheral blood smear - identify target cells, polychromasia, or other RBC abnormalities
- Additional Hemolysis Workup Tests: Serum bilirubin (total and indirect) - assess for jaundice; Haptoglobin - decreased with hemolysis; Lactate dehydrogenase (LDH) - elevated with hemolysis; Urinalysis - check for hemoglobinuria or myoglobinuria; Reticulocyte count - elevated during hemolytic episodes
- Genetic Testing and Variant Identification: DNA sequencing to identify specific G6PD mutation; variant classification to predict severity (Class I-IV); important for genetic counseling and family members; helps predict response to specific triggers
- Tests for Chronic Hemolysis Complications: Serum iron and ferritin - assess iron overload from transfusions; Liver function tests (AST, ALT, GGT) - monitor liver function; Abdominal ultrasound - screen for gallstones and splenomegaly; Renal function tests (creatinine, BUN) - baseline kidney function assessment
- Neonatal Screening Follow-Up: Confirm positive newborn screening with repeat G6PD testing at 3-6 months (after fetal hemoglobin decline); Bilirubin monitoring for jaundice; Pediatric evaluation and counseling
- Acute Hemolytic Episode Workup: Repeat G6PD testing after recovery from acute episode (values may be falsely normal during crisis); Additional hemolysis markers; Metabolic panel and kidney function; Blood cultures if infection suspected; Medication review to identify potential triggers
- Complementary Testing for Diagnosis: Direct antiglobulin test (Coombs test) - typically negative in G6PD deficiency, helps rule out immune hemolysis; Osmotic fragility test - normal in G6PD, helps exclude hereditary spherocytosis; Eosin-5'-maleimide (EMA) binding test - alternative screening for RBC membrane defects
- Monitoring Frequency for Diagnosed G6PD Deficiency: Asymptomatic patients: Annual CBC and health maintenance; Symptomatic patients: Quarterly evaluation; During infection or illness: Immediate assessment; Before new medication initiation: Review against G6PD-triggering drug list; Pregnancy: Enhanced monitoring in G6PD-deficient women
- Family Screening: Testing for biological relatives (parents, siblings, children); X-linked inheritance pattern determines who requires testing; Genetic counseling for reproductive planning; Risk assessment for family members
Section 6: Fasting Required?
- Fasting Requirement: No - Fasting is NOT required for G6PD testing
- Specimen Collection Details: Type of specimen: EDTA whole blood (lavender top tube); Amount: Typically 3-5 mL of whole blood; Tube must contain EDTA anticoagulant to prevent clotting
- Patient Preparation Requirements: No special fasting required; Patient can eat and drink normally before test; No need to restrict fluids; Can take regular medications unless specifically directed otherwise by physician
- Medications to Avoid Before Testing: Generally no medication restrictions; However, if testing to confirm acute hemolysis-causing drug, may need to avoid that specific drug before testing; If possible, collect specimen when not taking suspected triggering medications; Timing does NOT affect enzyme levels, only acute hemolysis markers
- Important Timing Considerations: Avoid testing during or immediately after acute hemolytic episode (first 4-6 weeks) - false normal results due to preferential destruction of deficient RBCs; Optimal timing: 3-6 months after hemolytic episode for accurate deficiency assessment; Recent transfusion may mask deficiency - wait 3 months before testing if possible
- Special Instructions for Specific Populations: Newborns: Can be tested at any time, no fasting needed; Neonatal screening via heel prick acceptable; Infants on feeding schedule: No adjustment needed; Pregnant women: No special requirements; Elderly patients: No modifications needed
- Specimen Handling and Storage: Refrigerate at 2-8°C immediately after collection; Send to laboratory within 24 hours; Do not freeze without special instructions; Keep tube sealed and upright during transport; Maintain proper chain of custody
- Pre-Collection Communication: Inform patient that venipuncture will be performed; Explain the purpose of testing; Mention any recent transfusions or acute illness; Note current medications; Disclose any hemolytic episodes within last 3 months

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