Glucose-6-phosphate dehydrogenase deficiency: Screening and Women

Glucose-6-phosphate dehydrogenase (G6PD) deficiency affects an estimated 400 million people globally, making it the most common enzyme disorder in humans. Glucose-6-phosphate dehydrogenase deficiency is an inherited enzyme disorder most common in malaria-endemic areas that can cause hemolytic anemia, hemolytic crises in reaction to certain drugs or fava beans, and neonatal jaundice, a condition that can cause brain damage, death, and or other disorders and complications. 

This is the second blog of our Glucose-6-Phosphate Deficiency series. You can read more about the effects of G6PD deficiency on the human body, its prevalence, and the reason it affects certain people in the first blog of our Glucose-6-phosphate dehydrogenase deficiency series. 

Due to the high prevalence of people with G6PD deficiency in malaria-endemic areas and the fact that certain antimalarial drugs may trigger a life-threatening hemolytic event in people with G6PD deficiency, testing for the disorder is especially pertinent to public health. However, the issue of sex plays an issue in testing. 

For males, testing for G6PD deficiency is simple. Males can be tested for G6PD deficiency using a fluorescent spot test or a spectrophotometric assay. The fluorescent spot test and the spectrophotometric assay detect the presence of NADPH in the blood, a product of Glucose-6-phosphate dehydrogenase. These tests are fast, inexpensive, easy to administer, and do not require a developed infrastructure to perform. They are reliable to test for hemizygous G6PD deficiency in males and homozygous G6PD deficiency in females. However, the fluorescent spot test is not sensitive enough to detect for heterozygous G6PD deficiency in females due to the large number of healthy erythrocytes in their blood. Because of this, a heterozygous G6PD deficient female may receive result indicating that they are negative for G6PD deficiency, despite being at risk for neonatal jaundice, hemolytic anemia, and hemolytic crises from treatment with certain immunosuppressant and antimalarial medications or ingestion of fava beans. 

Females must seek alternative testing for G6PD deficiency. A cytochemical assay and a light microscope can be used to detect G6PD deficiency in heterozygous and homozygous females, as well as hemizygous males. This technique stains erythrocytes that exhibit G6PD activity without coloring erythrocytes that are G6PD deficient. By examining a blood sample mixed with tetranitro blue tetrazolium and counting the number of stained and unstained erythrocytes, it can be determined if the patient is heterozygous G6PD deficient, homozygous G6PD deficient, not G6PD deficient or hemizygous G6PD deficient if they are male. However, this test is more time consuming, more difficult to perform, and more costly than the fluorescent spot test or the spectrophotometric assay. 

Since the majority of those with G6PD deficiency live in malaria-endemic areas and G6PD deficiency makes antimalarial drugs deadly to the patient, it is especially important for individuals to know whether or not they are G6PD deficient. Many times it is not possible for a patient to receive G6PD testing when they contract malaria, due to issues of accessibility in areas with underfunded health systems and the time and expertise required to perform the test. 

When there is opportunity for testing for G6PD deficiency, male patients are eligible to accurately be assessed using any G6PD deficiency testing method. Since males can either be hemizygous for G6PD deficiency or not G6PD deficient, the best method for testing for G6PD deficiency in male patients is the fluorescent spot test, as it is the least expensive of all of the testing methods. Both the fluorescent spot test and the spectrophotometric assay are quick, easy, and sufficiently accurate to detect for hemizygous G6PD deficiency in males. Male individuals could also take advantage of a rapid test, which could offer an even faster and automated testing option. 

Availability for G6PD deficiency testing for females is lower, as they require the most costly and most difficult test to perform cytochemical assay for an accurate result. This creates inequality in testing for G6PD deficiency. A cytochemical assay kit could potentially offer a solution to simplify the process and shorten the time required to perform a cytochemical assay so a female patient could be tested quickly and accurately, even by someone without medical experience or training. 

UN Photo Ivorian women MCH, by Hien Macline

Sources

Anderle, A., Bancone, G., Domingo, G. J., Gerth-Guyette, E., Pal, S., & Satyagraha, A. W. (2018). Point-of-Care Testing for G6PD Deficiency: Opportunities for Screening.International journal of neonatal screening,4(4), 34. 

Nkhoma, E. T., Poole, C., Vannappagari, V., Hall, S. A., & Beutler, E. (2009). The global prevalence of glucose-6-phosphate dehydrogenase deficiency: A systematic review and meta-analysis. Blood Cells, Molecules, and Diseases, 42(3), 267–278. doi:10.1016/j.bcmd.2008.12.005

Peters, A. L., & Van Noorden, C. J. (2009). Glucose-6-phosphate dehydrogenase deficiency and malaria: cytochemical detection of heterozygous G6PD deficiency in women.The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society,57(11), 1003–1011. https://doi.org/10.1369/jhc.2009.953828

WHO Working Group. (1989). Glucose-6-phosphate dehydrogenase deficiency. Bulletin of the World Health Organization, 67(6), 601–611.