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Strip test to diagnose Sickle Cell Anemia

Introduction

Sickle cell anemia (SCA)is caused by a mutation of the beta globin gene. It affects about 300,000 newborns each year, and includes symptoms such as severe anemia, pain and decreased immune function.
Individuals who are homozygous for the sickle cell gene mutation produce only HbS (genotype SS) are affected by the disease whereas heterozygotes, producing both HbA and HbS (genotype AS), have sickle cell trait but show no symptoms of the disease as they produce both the wild-type (HbA) and the mutant (HbS) form of the gene.
Most countries affected by the disease such as the sub-Saharan Africa, lack robust neonatal screening programs needed to identify patients in need of treatment.
In this paper, Bond et al. developed and evaluated a point-of-care strip test that allows differentiating sickle cell anemia (SCA) from sickle cell trait (SCT) in only 15 minutes with a simple visual inspection.
The test is able to identify individuals with SCA in only 15 minutes using undiluted whole blood.
This point-of-care strip is based on a competitive lateral flow assay where target specific antibodies have been conjugated to Expedeon Latex blue beads.
Results

A Lateral flow immunoassay was performed to establish whether HbA was present in the blood sample.
Sample blood was mixed in a tube with two populations of Innova blue latex beads: one conjugated to mouse anti-HbA antibodies and the other to mouse anti-HbS antibodies. This mixture was applied to a lateral flow strip on which HbS and HbA have been dried upon.
When placed in running buffer, the beads flow along the strip and bind to the capture proteins if no antigen is present. If the corresponding antigen is present, the beads are prevented from binding to the capture protein.

To provide evidence that this point-of-care system could be used for diagnostic purposes, the authors established a threshold for identifying positive lines (to avoid false positives), the amount of blood volume required for a single test and the effects of varying the ratio of HbA to HbS at optimal volume. According to their results, if HbS is present in the sample at a concentration below 20%, the sample is incorrectly classified as normal.
Finally, programmatic analysis quantification achieves 98% accuracy, 98% sensitivity and 100% specificity for identifying SCA.

Conclusion

The authors developed a point-of-care system that allows identification of SCA patients in only 15 minutes with a cost per-strip of approximately $2.60. Despite the test cannot correctly identify clinical specimens of SCT containing 24-45% HbS, the kit offers several promising advantages compared to competitive kits already available on the market.

Future directions

Further research needs to be done to more fully examine the effects of varying haemoglobin concentration and the percent of non-detectable hemoglobins. This test will not able to diagnose the condition in the presence of large quantities of transfused normal blood.

Expedeon Blue Latex Conjugation Kit
The test relies on our blue Latex beads labelling kit that compared to other kits available on the market offers several advantages, including:

  • Quick and easy to use – save time, no specialist knowledge required
  • Covalent bond – highly stable conjugates
  • No extensive pH optimization required – save precious antibody / protein
  • Resistant to aggregation -generation of high quality data

In addition to blue, Innova’s Latex beads are also available in black and red, making these kits ideal for multiplexing.

 

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