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Nucleated Red Blood Cells
Nucleated red blood cells (nRBCs), which are larger and more immature than other blood cell types (such as reticulocytes) and mature red blood cells, can be used for monitoring and diagnosing maternal, fetal, and neonatal health issues. Strategies that have been used in the past to isolate nRBCs have been limited to the low recovery of cells (Purwosunu 2006). There is now a new technique for isolating nRBCs from maternal blood. The new technique is called a microfluidic device.
For over three decades red blood cells in the maternal circulation have been used for prenatal diagnosis. Therefore, a technique that is good at isolating nRBCs is important. A method that is used frequently to sort non-maternal nRBCs and white blood cells includes a method called density gradient separation. The density gradient separation works by separating cells according to their weight or size.
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How the Microfluidic Device Works
The new microfluidic device has been shown to maintain a high recovery and puring rate of nRBCs from maternal blood circulation. The microfluidic device works by using a two step process. The first step involves a cell separation microchip (CSM) that separates blood cells based on size and the ability for the cell to deform. The second step involves a hemoglobin enrichment (HE) module to separate cell fractions based on having a nucleus and a protein called hemoglobin. The CSM separates blood cells that contain a nucleus and blood cells that don't contain a nucleus. The HE step involves using the magnetic properties of nRBCs and convert the protien hemoglobin to methemoglobin after being treated with sodium nitrate. The nRBCs are then passed through a magnetic column and retained for collection (Huang 2008).
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Collecting the RBCs after the CSM and HE Steps
Collecting the blood samples works by having the blood pass through microposts under laminar flow at a small angle relative to the array. Cells that are small with the respect of the flow stream drift along the flow and stay in the stream. The cells that are larger then the flow stream are not able to enter the micropost. Thus, there is a pore size that allows for cells to pass or not pass through the micropost. The microfluidic device allows for a 10 to 20 fold increase in the number of nRBCs collected compared to other methods (Huang 2008).
It has been suggested that an increase in the number of maternally circulating nRBCs from a normal level could indicate the presence of a fetal complication (Mavrou 2007).
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Huang R, Barber T.A., Schmidt M.A., Tompkins R.G., Toner M, Bianchi D.W., Kapur R, Flejter W.R. 2008. A microfluidics approach for the isolation of nucleated red blood cells (NRBCs) from the peripheral blood of pregnant women. Prenatal Diagnosis 28 : 892–899.
Mavrou A, Kouvidi E, Antsaklis A, Souke A, Kitsiou Tzeli S, Kolialexi A. 2007. Identification of nucleated red blood cells in maternal circulation: A second step in screening for fetalaneuploidies and pregnancy complications. Prenatal Diagnosis 27: 150-153
Purwosunu Y, Sekizawa A, Koide K, Okazaki S, Farina A, Okai T. 2006a. Clinical potential for noninvasive prenatal diagnosis through detection of fetal cells in maternal blood. Taiwan Journal of Obstetrics and Gynecology 45:10–20.