Many diagnostic tests in a conventional clinical laboratory are performed on blood plasma because changes in its composition often reflect the current status of pathological processes throughout the body. Recently, a significant research effort has been invested into the development of microfluidic paper-based analytical devices (μPADs) implementing these conventional laboratory tests for point-of-care diagnostics in resource-limited settings. This paper describes the use of red blood cell (RBC) agglutination for separating plasma from finger-prick volumes of whole blood directly in paper, and demonstrates the utility of this approach by integrating plasma separation and a colorimetric assay in a single μPAD. The μPAD was fabricated by printing its pattern onto chromatography paper with a solid ink (wax) printer and melting the ink to create hydrophobic barriers spanning through the entire thickness of the paper substrate. The μPAD was functionalized by spotting agglutinating antibodies onto the plasma separation zone in the center and the reagents of the colorimetric assay onto the test readout zones on the periphery of the device. To operate the μPAD, a drop of whole blood was placed directly onto the plasma separation zone of the device. RBCs in the whole blood sample agglutinated and remained in the central zone, while separated plasma wicked through the paper substrate into the test readout zones where analyte in plasma reacted with the reagents of the colorimetric assay to produce a visible color change. The color change was digitized with a portable scanner and converted to concentration values using a calibration curve. The purity and yield of separated plasma was sufficient for successful operation of the μPAD. This approach to plasma separation based on RBC agglutination will be particularly useful for designing fully integrated μPADs operating directly on small samples of whole blood.

Although effective low-cost interventions exist, child mortality attributable to sickle cell disease (SCD) remains high in low-resource areas due, in large part, to the lack of accessible diagnostic methods. The presence of dense (ρ > 1.120 g/cm 3 ) cells is characteristic of SCD. The fluid, self-assembling step-gradients in density created by aqueous multiphase systems (AMPSs) identifies SCD by detecting dense cells. AMPSs separate different forms of red blood cells by density in a microhematocrit centrifuge and provide a visual means to distinguish individuals with SCD from those with normal hemoglobin or with nondisease, sickle-cell trait in under 12 min. Visual evaluation of a simple two-phase system identified the two main subclasses of SCD [homozygous (Hb SS) and heterozygous (Hb SC)] with a sensitivity of 90% (73-98%) and a specificity of 97% (86-100%). A threephase system identified these two types of SCD with a sensitivity of 91% (78-98%) and a specificity of 88% (74-98%). This system could also distinguish between Hb SS and Hb SC. To the authors' knowledge, this test demonstrates the first separation of cells by density with AMPSs, and the usefulness of AMPSs in point-of-care diagnostic hematology.polymers | erythrocytes | sickle cell anemia | cell sorting | density gradient centrifugation

The measurements performed using the AMVN device confirm a significant decline in the rheologic properties of RBCs in units nearing expiration and demonstrate the sensitivity of the device to these storage-induced changes. The AMVN device may be useful for testing the effect of new storage conditions, additive solutions, and rejuvenation strategies on the rheologic properties of stored RBCs in vitro.

BackgroundSickle cell disease is one of the most common inherited blood disorders. Universal screening and early intervention have significantly helped to reduce childhood mortality in high-resource countries. However, persons living in low-resource settings are often not diagnosed until late childhood when they present with clinical symptoms. In addition, confirmation of disease in affected individuals in the urgent care setting is limited in both high- and low-resource areas, often leading to delay in treatment. All of the current diagnostic methods rely on advanced laboratory systems and are often prohibitively expensive and time-consuming in low-resource settings. To address this need, the Sickle SCAN™ test has been developed to diagnose sickle cell disease and sickle cell trait at the point of care without electricity or advanced equipment.MethodsThis study was conducted to evaluate and validate the diagnostic accuracy of the Sickle SCAN™ test, a novel point of care test for sickle cell disease. Thus, we describe the laboratory testing and clinical validation of the Sickle SCAN™ test in individuals >1 year of age using capillary blood. The Sickle SCAN™ test was created using advanced, qualitative lateral flow technology using capillary blood to identify the presence of hemoglobin A, S, and C allowing for detection of results with the naked eye.ResultsLaboratory testing using venous blood demonstrated 99 % sensitivity and 99 % specificity for the diagnosis of HbSS, HbAS, HbSC, HbAC, and HbAA. Seventy-one subjects underwent capillary blood sampling at the point of care for further validation. This test detected the correct A, S, and C presence with an overall diagnostic accuracy of 99 % at the bedside.ConclusionThe Sickle SCAN™ test has the potential to significantly impact the diagnosis and treatment for sickle cell disease worldwide as well as enhance genetic counseling at the point of care. Further validation testing will be conducted in newborns in resource-poor settings in upcoming studies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12916-015-0473-6) contains supplementary material, which is available to authorized users.

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