OVERVIEW
Fava bean disease, commonly known as “Hu Dou Huang”, is a disease caused by erythrocyte glucose-6-phosphate dehydrogenase (G6PD) deficiency, which manifests itself as acute intravascular hemolysis that occurs suddenly after consumption of fresh fava beans in the presence of hereditary glucose-6-phosphate dehydrogenase (G6PD) deficiency. It is common in certain areas of Guangxi, the Li ethnic group on Hainan Island and the Dai ethnic group in Yunnan Province in China, and is less common north of the Huaihe River. It is more common in children under the age of 10, and there are more males than females. 40% of the patients have a family history. The onset of the disease is concentrated in the season of fava bean ripening (March to May) every year.
Etiology
The pathogenesis is complex. Reduced nicotinamide adenine dinucleotide phosphate (NADPH) and reduced glutathione (GSH) in G6PD-deficient erythrocytes can cause direct oxidative damage to the sulfhydryl groups of the cell membrane when encountering fava beans and certain factors, and produce methemoglobin and denatured bead protein, i.e., Heinz bodies. The above changes can lead to lipid peroxidation damage of the erythrocyte membrane and hemolysis. G-6-PD has the function of protecting normal erythrocytes from oxidative damage, and fresh fava beans are a very strong oxidizing agent, so when G-6-PD is deficient, the erythrocytes will be destroyed and the disease will occur.
Symptoms
There is a close relationship between the onset of the disease and the season, and the peak of the disease occurs every year during the bean ripening season (March to May).
The onset of the disease is rapid, generally 2 hours to a few days after eating fresh fava beans and their products (generally 1 to 2 days, the longest 15 days) suddenly occurred acute intravascular hemolysis. The degree of hemolysis has nothing to do with the amount of fava beans eaten. It is a self-limiting process, and hemolysis lasts for about a week.
The main symptoms are dizziness, tiredness and weakness, pallor, fever, nausea and vomiting, thirst, lack of appetite, abdominal pain, jaundice, and the color of urine can be tea-colored, red wine-colored, blood-red, soy sauce-colored. Severe cases may have oliguria, coma, convulsions, delirium, dehydration, acidosis, and acute renal failure. Physical examination half of the cases have hepatomegaly and a few cases have splenomegaly.
Examination
1. Blood picture
① Hemoglobin decreases sharply. In severe cases, the hemoglobin drops to less than 30g/L; ② red blood cell count drops to less than 0.5×1012/L; ③ reticulocytes increase >0.20; ④ nucleated red blood cells can be seen in peripheral blood smear; ⑤ leukocyte count rises, up to (10～20)×109/L, and even leukemia-like reaction; ⑥ platelet count is normal or elevated.
2. Bone marrow
The red lineage is obviously hyperplastic, with the middle and late erythrocyte hyperplasia predominating. The granulocyte-red ratio is reduced or inverted.
3. Urine examination
① urine soy sauce color, strong tea color, red wine color, blood red, etc.; ② urine occult blood test can be up to 60% ~ 70%; ③ urine hemoglobin, urine ferritin and urine bilirubin and are positive, urine bilirubin negative.
4. Plasma free hemoglobin, serum binding bead protein, blood free bilirubin
Plasma free hemoglobin is increased, serum conjugated albumin is decreased, and blood free bilirubin is increased.
5. Erythrocyte G6PD activity measurement
The most reliable and the main diagnostic basis. There are many methods, but for this disease all kinds of results should be lower than 40% of the normal average. The enzyme activity during peak hemolysis and recovery period can be normal or close to normal, usually 2~3 months after acute hemolysis, the review can more accurately reflect the patient’s G6PD activity.
6.G6PD activity screening test
The commonly used tests in China are methemoglobin reduction test, fluorescence spot test, nitrotetrazolium blue paper method.
7. Erythrocyte Heinstein vesicle generation test
Count >5% has diagnostic significance. However, this test lacks specificity and can also be seen in hemolysis caused by other reasons.
Diagnosis
The G6PD mutation gene is on the X chromosome (Xq28) and is inherited in an X-linked incomplete dominant manner, more often in males than females. The disease is considered and investigated in those with a positive family history, a medical history characterized by acute hemolysis, and triggers such as fava bean consumption. The diagnosis is established by two moderate or one severe abnormalities in screening tests or by abnormal quantitative measurements.
Treatment
When the disease does not develop without a trigger, it is treated as normal and requires no special treatment. Avoid fava beans.
For acute hemolysis, the causative agent should be removed, and care should be taken to correct water, electrolyte, acid-base imbalance and renal insufficiency. Transfusion of red blood cells (avoid blood of relatives) and use of glucocorticoids may improve the condition.
Hemolysis with nuclear jaundice occurs in newborns with this disease, and can be treated with blood exchange, phototherapy or phenobarbital.