Researchers Develop Test for SCA to be Used in Low-Resource Settings

Researchers have developed an accurate, low–cost potential test for diagnosing people with sickle cell anemia. The test, based on a lateral flow strip, is designed for use in areas where SCA treatment exists but testing methods are inaccessible, such as sub-Saharan Africa, where SCA is prominent.

While researchers were optimistic about the results, they recommended further testing to ensure the test’s reliability in warm climates and in the field.

The study, “Towards a point-of-care strip test to diagnose sickle cell anemia,” was published in PLOS One.

Individuals who have a recessively inherited mutation (two deficient copies) of the beta globin gene instead of normal adult hemoglobin (HbA) produce sickle hemoglobin (HbS) that causes sickle cell anemia (SCA). Individuals with one good and one bad copy produce both HbA and HbS and have sickle cell trait (SCT). Normally, these individuals do not show symptoms of the disease but can transmit the abnormal gene to their children.

People who are carriers of the sickle cell disease have some protective advantage against malaria. Therefore, the prevalence of sickle cell carriers is high in malaria-endemic regions, such as certain regions in Africa.

In sub-Saharan Africa, an estimated 75.5% of newborns have sickle cell disease. While low-cost treatments are available in these areas, low-cost methods to readily diagnose the disease are lacking.

This lack of efficient screening programs results in only 20–50% of affected children surviving to the age of 5. In most cases, sickled red blood cells damage the spleen and cause infections that lead to death. Thus, a point-of-care diagnostic tool suitable for newborn screening in low-resource regions is urgently needed.

Currently, several sensitive methods exist to diagnose sickle cell disease that distinguish between normal, SCT, and SCA samples. But these methods require expensive equipment and extensive training and are not suitable for point-of-care use, particularly in low–resource settings.

The study describes the development and evaluation of an automated method using a lateral flow strip to screen patients with sickle cell disease. The strip was initially evaluated by testing its performance with different volumes of blood and HbA and HbS ratios from discarded patient and volunteer blood samples. Its performance was then evaluated with clinical samples of SCA, SCT, and normal blood.

The lateral flow test identified SCA in patient samples with 90% sensitivity and 100% specificity, with either visual or automated interpretation. The test can accept small volumes of undiluted whole blood and provides an answer in 10 minutes at a cost of about $2.60 per strip. Researchers believe eventually that cost can be reduced to as low as $0.15 per strip.

While other diagnostic tests, such as a paper test and Sickle SCAN, can distinguish between normal, SCT, and SCA blood, the lateral flow strip cannot discriminate between SCT and normal blood, making it difficult to diagnose SCT.

But the more precise tests require the user to dilute the blood before testing is conducted. With the lateral flow strip, however, it is possible to use undiluted blood, which is then mixed with latex beads containing anti-HbS and anti-HbA antibodies to detect SCA.

The authors acknowledge limitations to the lateral flow strip in its current form, such as the dilution effect of fetal hemoglobin (HbF) or other mutations in the detectable hemoglobins (HbA and HbS), as well as interference by non-specific binding with test components.

Researchers recommend further testing to confirm that the lateral flow strip could be used as a low-cost, point–of–care diagnostic method for identifying SCA.

“The accuracy of the strip should be assessed in areas of low and high prevalence for SCA, as well as under conditions of varying heat and humidity,” the authors stated.