What to expect from a blood test for G6PD deficiency

A G6PD blood test uses a small blood sample to measure enzyme activity in red blood cells. The sample is usually taken from a vein in your arm after the skin is cleaned. The needle may sting briefly, and a little bruising can follow. Ask the testing service whether any preparation is needed, and bring a list of medicines and supplements.

G6PD helps red blood cells handle oxidative stress. Lower enzyme activity can support a diagnosis of G6PD deficiency, an inherited condition that may make red blood cells break down after certain medicines, foods, or infections. Testing during or soon after a haemolytic episode can sometimes be difficult to interpret because younger red blood cells may have different enzyme activity. A clinician may recommend repeat or additional testing when the result does not fit the clinical picture.

Tell your clinician about recent jaundice, dark urine, fever, infection, transfusion, and every medicine or supplement you use. Do not stop prescribed treatment without advice. If deficiency is confirmed, ask which medicines and foods should be avoided and whether relatives should discuss testing. Keep the result available for future clinicians, particularly before a new prescription or procedure.

Seek urgent medical help for yellowing of the skin or eyes, very dark urine, severe tiredness, breathlessness, fainting, confusion, or a fast heartbeat, especially after an infection, medicine, or food trigger. These can indicate rapid red-cell breakdown and need assessment rather than waiting for a routine appointment.

Ask whether recent illness or transfusion could affect timing, how the laboratory will report enzyme activity, what triggers matter for you, and how to share the result with pharmacists and emergency clinicians.