A rapid paper-based test for quantifying sickle hemoglobin in blood samples from patients with sickle cell disease

The flow of sickle blood in glass capillaries: Fundamentals and potential applications

We have characterized the imbibed horizontal flow of sickle blood into 100-μm-diameter glass capillaries. We find that blood containing sickled cells typically traverses the capillaries between three and four times as slowly as oxygenated cells from the same patient for all genotypes tested, including SS, AS, SC and Sβ+ thalassemia blood. Blood from SS patients treated with hydroxyurea has a viscosity intermediate between the SS and AA values. Blood containing cells that are not rigidified, such as normal red cells or oxygenated sickle cells, follows a simple Lucas-Washburn flow throughout the length of the 3-cm capillary. By fitting the flexible-cell data to the Lucas-Washburn model, a viscosity can be derived that is in good agreement with previous measurements over a range of volume fractions and is obtained using an apparatus that is far more complex. Deoxygenation sickles and thus rigidifies the cells, and their flow begins as Lucas-Washburn, albeit with higher viscosity than flexible cells. However, the flow further slows as a dense mass of cells forms behind the meniscus and increases in length as flow progresses. By assuming that the dense mass of cells exerts a frictional force proportional to its length, we derive an equation that is formally equivalent to vertical imbibition, even though the flow is horizontal, and this equation reproduces the observed behavior well. We present a simple theory using activity coefficients that accounts for this viscosity and its variation without adjustable parameters. In the course of control experiments, we have found that deoxygenation increases the flexibility of normal human red cells, an observation only recently published for mouse cells and previously unreported for human erythrocytes. Together, these studies form the foundation for an inexpensive and rapid point-of-care device to diagnose sickle cell disease or to determine blood viscosity in resource-challenged settings.

Techniques for the Detection of Sickle Cell Disease: A Review

Sickle cell disease (SCD) is a widespread disease caused by a mutation in the beta-globin gene that leads to the production of abnormal hemoglobin called hemoglobin S. The inheritance of the mutation could be homozygous or heterozygous combined with another hemoglobin mutation. SCD can be characterized by the presence of dense, sickled cells that causes hemolysis of blood cells, anemia, painful episodes, organ damage, and in some cases death. Early detection of SCD can help to reduce the mortality and manage the disease effectively. Therefore, different techniques have been developed to detect the sickle cell disease and the carrier states with high sensitivity and specificity. These techniques can be screening tests such as complete blood count, peripheral blood smears, and sickling test; confirmatory tests such as hemoglobin separation techniques; and genetic tests, which are more expensive and need to be done in centralized labs by highly skilled personnel. However, advanced portable point of care techniques have been developed to provide a low-cost, simple, and user-friendly device for detecting SCD, for instance coupling solubility tests with portable devices, using smartphone microscopic classifications, image processing techniques, rapid immunoassays, and sensor-based platforms. This review provides an overview of the current and emerging techniques for sickle cell disease detection and highlights the different potential methods that could be applied to help the early diagnosis of SCD.

Emerging point-of-care technologies for sickle cell disease diagnostics

Sickle cell disease (SCD) is a serious and life-threatening disorder. SCD is considered a public health issue affecting 25% of the population in Central and West Africa. Some countries in this region lack the necessary resources to treat and diagnose many diseases including SCD. Current methods for screening SCD are time-consuming and require expensive laboratory equipment and facilities. This leads to an inability to diagnose the disease early. Lack of early diagnosis and treatment can lead to childhood death. The number of childhood deaths is significantly higher in developing countries. There is unmet need to develop novel methods for diagnosing and monitoring SCD that are both cost effective and portable. The point-of-care (POC) platforms provide the cost effectiveness and portability that allows for the potential diagnosis of millions of people in countries with few resources. In this review, we summarized the important features, benefits, limitations and potential of POC devices. We conducted a comprehensive literature analysis to compare the sensitivity and specificity of several POC diagnostics developed for SCD with a focus on their usages in resource limited settings.

Paper-Based Diagnostics: Rethinking Conventional Sickle Cell Screening to Improve Access to High-Quality Health Care in Resource-Limited Settings

Every year, hundreds of thousands of children worldwide are born with sickle cell disease, a genetic disorder that impacts the hemoglobin molecules in blood. If left undiagnosed and untreated, most affected children will die before reaching the age of five. However, highly accurate diagnostic methods and effective treatment regimens for sickle cell disease have been known for many years, and children who receive early diagnosis and subsequent comprehensive care survive well into adulthood-as evidenced by the tremendous success of universal newborn screening programs in North America and Europe.

Substituting Sodium Hydrosulfite with Sodium Metabisulfite Improves Long-Term Stability of a Distributable Paper-Based Test Kit for Point-of-Care Screening for Sickle Cell Anemia

Sickle cell anemia (SCA) is a genetic blood disorder that is particularly lethal in early childhood. Universal newborn screening programs and subsequent early treatment are known to drastically reduce under-five SCA mortality. However, in resource-limited settings, cost and infrastructure constraints limit the effectiveness of laboratory-based SCA screening programs. To address this limitation our laboratory previously developed a low-cost, equipment-free, point-of-care, paper-based SCA test. Here, we improved the stability and performance of the test by replacing sodium hydrosulfite (HS), a key reducing agent in the hemoglobin solubility buffer which is not stable in aqueous solutions, with sodium metabisulfite (MS). The MS formulation of the test was compared to the HS formulation in a laboratory setting by inexperienced users (n = 3), to determine visual limit of detection (LOD), readout time, diagnostic accuracy, intra- and inter-observer agreement, and shelf life. The MS test was found to have a 10% sickle hemoglobin LOD, 21-min readout time, 97.3% sensitivity and 99.5% specificity for SCA, almost perfect intra- and inter-observer agreement, at least 24 weeks of shelf stability at room temperature, and could be packaged into a self-contained, distributable test kits comprised of off-the-shelf disposable components and food-grade reagents with a total cost of only $0.21 (USD).

A Paper-Based Test for Screening Newborns for Sickle Cell Disease

The high cost, complexity and reliance on electricity, specialized equipment and supplies associated with conventional diagnostic methods limit the scope and sustainability of newborn screening for sickle cell disease (SCD) in sub-Saharan Africa and other resource-limited areas worldwide. Here we describe the development of a simple, low-cost, rapid, equipment- and electricity-free paper-based test capable of detecting sickle hemoglobin (HbS) in newborn blood samples with a limit of detection of 2% HbS. We validated this newborn paper-based test in a cohort of 159 newborns at an obstetric hospital in Cabinda, Angola. Newborn screening results using the paper-based test were compared to conventional isoelectric focusing (IEF). The test detected the presence of HbS with 81.8% sensitivity and 83.3% specificity, and identified SCD newborns with 100.0% sensitivity and 70.7% specificity. The use of the paper-based test in a two-stage newborn screening process could have excluded about 70% of all newborns from expensive confirmatory testing by IEF, without missing any of the SCD newborns in the studied cohort. This study demonstrates the potential utility of the newborn paper-based test for reducing the overall cost of screening newborns for SCD and thus increasing the practicality of universal newborn SCD screening programs in resource-limited settings.

Emerging point-of-care technologies for sickle cell disease screening and monitoring

INTRODUCTION

Sickle Cell Disease (SCD) affects 100,000 Americans and more than 14 million people globally, mostly in economically disadvantaged populations, and requires early diagnosis after birth and constant monitoring throughout the life-span of the patient. Areas covered: Early diagnosis of SCD still remains a challenge in preventing childhood mortality in the developing world due to requirements of skilled personnel and high-cost of currently available modalities. On the other hand, SCD monitoring presents insurmountable challenges due to heterogeneities among patient populations, as well as in the same individual longitudinally. Here, we describe emerging point-of-care micro/nano platform technologies for SCD screening and monitoring, and critically discuss current state of the art, potential challenges associated with these technologies, and future directions. Expert commentary: Recently developed microtechnologies offer simple, rapid, and affordable screening of SCD and have the potential to facilitate universal screening in resource-limited settings and developing countries. On the other hand, monitoring of SCD is more complicated compared to diagnosis and requires comprehensive validation of efficacy. Early use of novel microdevices for patient monitoring might come in especially handy in new clinical trial designs of emerging therapies.

Characteristics of a rapid, point-of-care lateral flow immunoassay for the diagnosis of sickle cell disease

Sickle cell disease (SCD) is a common and life-threatening hematological disorder, affecting approximately 400,000 newborns annually worldwide. Most SCD births occur in low-resource countries, particularly in sub-Saharan Africa, where limited access to accurate diagnostics results in early mortality. We evaluated a prototype immunoassay as a novel, rapid, and low-cost point-of-care (POC) diagnostic device (Sickle SCAN) designed to identify HbA, HbS, and HbC. A total of 139 blood samples were scored by three masked observers and compared to results using capillary zone electrophoresis. The sensitivity (98.3-100%) and specificity (92.5-100%) to detect the presence of HbA, HbS, and HbS were excellent. The test demonstrated 98.4% sensitivity and 98.6% specificity for the diagnosis of HbSS disease and 100% sensitivity and specificity for the diagnosis of HbSC disease. Most variant hemoglobins, including samples with high concentrations of HbF, did not interfere with the ability to detect HbS or HbC. Additionally, HbS and HbC were accurately detected at concentrations as low as 1-2%. Dried blood spot samples yielded clear positive bands, without loss of sensitivity or specificity, and devices stored at 37°C gave reliable results. These analyses indicate that the Sickle SCAN POC device is simple, rapid, and robust with high sensitivity and specificity for the detection of HbA, HbS, and HbC. The ability to obtain rapid and accurate results with both liquid blood and dried blood spots, including those with newborn high-HbF phenotypes, suggests that this POC device is suitable for large-scale screening and potentially for accurate diagnosis of SCD in limited resource settings.

Validation of a Low-Cost Paper-Based Screening Test for Sickle Cell Anemia

Background

The high childhood mortality and life-long complications associated with sickle cell anemia (SCA) in developing countries could be significantly reduced with effective prophylaxis and education if SCA is diagnosed early in life. However, conventional laboratory methods used for diagnosing SCA remain prohibitively expensive and impractical in this setting. This study describes the clinical validation of a low-cost paper-based test for SCA that can accurately identify sickle trait carriers (HbAS) and individuals with SCA (HbSS) among adults and children over 1 year of age.

Methods and Findings

In a population of healthy volunteers and SCA patients in the United States (n = 55) the test identified individuals whose blood contained any HbS (HbAS and HbSS) with 100% sensitivity and 100% specificity for both visual evaluation and automated analysis, and detected SCA (HbSS) with 93% sensitivity and 94% specificity for visual evaluation and 100% sensitivity and 97% specificity for automated analysis. In a population of post-partum women (with a previously unknown SCA status) at a primary obstetric hospital in Cabinda, Angola (n = 226) the test identified sickle cell trait carriers with 94% sensitivity and 97% specificity using visual evaluation (none of the women had SCA). Notably, our test permits instrument- and electricity-free visual diagnostics, requires minimal training to be performed, can be completed within 30 minutes, and costs about $0.07 in test-specific consumable materials.

Conclusions

Our results validate the paper-based SCA test as a useful low-cost tool for screening adults and children for sickle trait and disease and demonstrate its practicality in resource-limited clinical settings.

Sickle cell detection using a smartphone

Sickle cell disease affects 25% of people living in Central and West Africa and, if left undiagnosed, can cause life threatening "silent" strokes and lifelong damage. However, ubiquitous testing procedures have yet to be implemented in these areas, necessitating a simple, rapid, and accurate testing platform to diagnose sickle cell disease. Here, we present a label-free, sensitive, and specific testing platform using only a small blood sample (<1 μl) based on the higher density of sickle red blood cells under deoxygenated conditions. Testing is performed with a lightweight and compact 3D-printed attachment installed on a commercial smartphone. This attachment includes an LED to illuminate the sample, an optical lens to magnify the image, and two permanent magnets for magnetic levitation of red blood cells. The sample is suspended in a paramagnetic medium with sodium metabisulfite and loaded in a microcapillary tube that is inserted between the magnets. Red blood cells are levitated in the magnetic field based on equilibrium between the magnetic and buoyancy forces acting on the cells. Using this approach, we were able to distinguish between the levitation patterns of sickle versus control red blood cells based on their degree of confinement.