Why Do I Need a G6PD Test Before Starting Dapsone?

Dapsone is a highly effective medication for treating the intense, itchy rash of dermatitis herpetiformis, but before your doctor can prescribe it, they must ensure your red blood cells can handle the medication. Dapsone causes a type of chemical stress in the bloodstream known as oxidative stress ^[1]. Your body uses a specific enzyme called G6PD (glucose-6-phosphate dehydrogenase) to protect your red blood cells from this exact type of stress ^[2][3]. The G6PD blood test checks to see if your body makes enough of this protective enzyme. If you are deficient, taking dapsone could cause your red blood cells to break down rapidly—a severe and potentially life-threatening condition called hemolytic anemia ^[1][4]. The test results usually take a few days to return, during which time your doctor may suggest topical creams to help manage the itching.

The Role of the G6PD Enzyme

G6PD (glucose-6-phosphate dehydrogenase) is an enzyme that helps red blood cells function normally and defends them against harmful substances ^[2]. Some people are born with a genetic condition called G6PD deficiency, meaning their bodies produce lower amounts of this enzyme, or the enzyme doesn’t work as effectively as it should ^[4].

Most people with G6PD deficiency experience absolutely no symptoms in their daily lives and are usually unaware they have the condition. However, when exposed to certain triggers—such as infections, fava beans, or specific “oxidative” medications like dapsone—their unprotected red blood cells can become rapidly damaged and destroyed ^[1][3].

Note: If you are diagnosed with G6PD deficiency, you will need to avoid these triggers for life, regardless of how you treat your dermatitis herpetiformis.

The Risk of Hemolytic Anemia

If a person with low G6PD levels takes dapsone, the medication’s breakdown products (such as dapsone hydroxylamine) attack the unprotected red blood cells ^[1]. This triggers hemolytic anemia, a dangerous condition where red blood cells are destroyed much faster than the bone marrow can replace them ^[1][5].

Symptoms of acute hemolytic anemia can appear suddenly and may include:

• Extreme fatigue, dizziness, and weakness
• Pale or yellowish skin and eyes (jaundice)
• Dark, tea-colored urine
• Shortness of breath and rapid heartbeat

Because this reaction can be so severe, checking your G6PD levels is a mandatory safety measure before you can begin taking dapsone ^[4]. If the test shows you are deficient, your doctor will discuss alternative oral medications that can help control the blistering rash safely while you wait for your gluten-free diet to take effect ^[6].

Monitoring Your Blood During Treatment

If your G6PD blood test comes back normal, your doctor can safely prescribe dapsone. However, even with normal G6PD levels, you will still need regular blood tests while taking the medication.

Dapsone naturally causes a mild, generally manageable amount of red blood cell breakdown in almost everyone who takes it ^[7][8]. It can also lead to a related condition called methemoglobinemia, where your blood temporarily carries oxygen less effectively ^[5]. Symptoms of this condition include shortness of breath, fatigue, and cyanosis—a bluish or grayish tint to the lips, skin, or nail beds.

Because of these expected side effects, your doctor will monitor your complete blood counts (CBC) frequently to ensure your body is tolerating the medication well and to adjust your dosage if necessary ^[5][6]. This usually involves weekly or biweekly lab tests during the first month of treatment, eventually stretching out to every few months once your body adjusts to the medication.