A cartridge system configured for use in a blood analyzer, the cartridge system comprising a cartridge and a fluid sampler, and being characterized in that the cartridge comprises: a substantially rigid portion; a flexible sheet fixed to the rigid portion, wherein the flexible sheet includes a deformable cap disposed over a depression formed in the rigid portion to form a first reservoir (1504, 1505); wherein the flexible sheet is selectively bonded to the rigid frame such that in at least one area the flexible sheet is permanently welded to the rigid portion and in at least one other area the flexible sheet is non-permanently welded thereby forming a peelable separation between the rigid portion and flexible sheet; at least one flow path (1516, 1517) formed in the rigid portion and configured to establish fluid communication between at least one inlet (1506, 1507) in the substantially rigid portion and the first reservoir; and the fluid sampler comprises: at least one capillary tube; and a seal/plug disposed within the at least one capillary tube, wherein a location of the seal/plug within the at least one capillary tube defines a fixed volume of sample fluid to be received by the at least one capillary tube; wherein the seal/plug is permeable to air such that when sample fluid enters the at least one capillary tube, air displaced by the sample fluid entering the at least one capillary tube is allowed to flow out of the at least one capillary tube through the seal/plug; and wherein the seal/plug is configured to be pushed by a plunger toward an end of the at least one capillary tube to deliver the fixed volume of sample fluid to the at least one flow path formed in the rigid portion of the cartridge. a substantially rigid portion; a flexible sheet fixed to the rigid portion, wherein the flexible sheet includes a deformable cap disposed over a depression formed in the rigid portion to form a first reservoir (1504, 1505); wherein the flexible sheet is selectively bonded to the rigid frame such that in at least one area the flexible sheet is permanently welded to the rigid portion and in at least one other area the flexible sheet is non-permanently welded thereby forming a peelable separation between the rigid portion and flexible sheet; at least one flow path (1516, 1517) formed in the rigid portion and configured to establish fluid communication between at least one inlet (1506, 1507) in the substantially rigid portion and the first reservoir; and at least one capillary tube; and a seal/plug disposed within the at least one capillary tube, wherein a location of the seal/plug within the at least one capillary tube defines a fixed volume of sample fluid to be received by the at least one capillary tube; wherein the seal/plug is permeable to air such that when sample fluid enters the at least one capillary tube, air displaced by the sample fluid entering the at least one capillary tube is allowed to flow out of the at least one capillary tube through the seal/plug; and wherein the seal/plug is configured to be pushed by a plunger toward an end of the at least one capillary tube to deliver the fixed volume of sample fluid to the at least one flow path formed in the rigid portion of the cartridge.