A method for performing a leukocyte differential assay on a milk sample, the method comprising: a) adding a milk sample to a microfluidic chamber assembly for use in performing leukocyte differential assay on a leukocyte containing fluid sample from a subject in a wedge sampling configuration chamber, the assembly comprising: i. a wedge base; ii. a wedge top having a first edge and an opposite second edge, said wedge top being positioned on the base such that the second edge is in an elevated configuration and the first edge is resting on the base, such that it forms a wedge shaped chamber sufficient for cell differential determination; iii. a wedge forming device which is a piece of cut out plastic sheeting having an adhesive backing, wherein the adhesive backing faces and is positioned against the wedge base so that it adheres, and wherein the second edge of the wedge top rests on the upper surface of the wedge forming device such that it forms the high point of the wedge shaped chamber; iv. a scored hold-down flap that is adhered to the wedge top and that holds the first edge of the wedge top securely against the wedge base, forming the bottom point of the wedge shaped chamber; v. two arms which hold the wedge top in place, said arms being folded over the wedge top and being adhered to the upper surface of the wedge top; and vi. the wedge forming device providing for a liquid entry well for liquid addition to the wedge shaped chamber, wherein at least one of the top or base is optically transparent, and wherein there is a leukocyte observation colorant positioned within the chamber; b) enumerating and calculating the leukocytes in the milk containing chamber into sub-populations; c) deriving a differential count of the leukocyte sub-populations. a) adding a milk sample to a microfluidic chamber assembly for use in performing leukocyte differential assay on a leukocyte containing fluid sample from a subject in a wedge sampling configuration chamber, the assembly comprising: i. a wedge base; ii. a wedge top having a first edge and an opposite second edge, said wedge top being positioned on the base such that the second edge is in an elevated configuration and the first edge is resting on the base, such that it forms a wedge shaped chamber sufficient for cell differential determination; iii. a wedge forming device which is a piece of cut out plastic sheeting having an adhesive backing, wherein the adhesive backing faces and is positioned against the wedge base so that it adheres, and wherein the second edge of the wedge top rests on the upper surface of the wedge forming device such that it forms the high point of the wedge shaped chamber; iv. a scored hold-down flap that is adhered to the wedge top and that holds the first edge of the wedge top securely against the wedge base, forming the bottom point of the wedge shaped chamber; v. two arms which hold the wedge top in place, said arms being folded over the wedge top and being adhered to the upper surface of the wedge top; and vi. the wedge forming device providing for a liquid entry well for liquid addition to the wedge shaped chamber, wherein at least one of the top or base is optically transparent, and wherein there is a leukocyte observation colorant positioned within the chamber; i. a wedge base; ii. a wedge top having a first edge and an opposite second edge, said wedge top being positioned on the base such that the second edge is in an elevated configuration and the first edge is resting on the base, such that it forms a wedge shaped chamber sufficient for cell differential determination; iii. a wedge forming device which is a piece of cut out plastic sheeting having an adhesive backing, wherein the adhesive backing faces and is positioned against the wedge base so that it adheres, and wherein the second edge of the wedge top rests on the upper surface of the wedge forming device such that it forms the high point of the wedge shaped chamber; iv. a scored hold-down flap that is adhered to the wedge top and that holds the first edge of the wedge top securely against the wedge base, forming the bottom point of the wedge shaped chamber; v. two arms which hold the wedge top in place, said arms being folded over the wedge top and being adhered to the upper surface of the wedge top; and vi. the wedge forming device providing for a liquid entry well for liquid addition to the wedge shaped chamber, wherein at least one of the top or base is optically transparent, and wherein there is a leukocyte observation colorant positioned within the chamber; b) enumerating and calculating the leukocytes in the milk containing chamber into sub-populations; c) deriving a differential count of the leukocyte sub-populations.