A disposable blood analysis cartridge for analyzing a blood sample including an optical absorbance measurement channel is described. The optical absorbance measurement channel includes a plasma separation region and at least one sub channel including a cuvette that is in fluid communication with the plasma separation region and configured to receive a plasma portion of a blood sample that has been passed through the plasma separation region. A negative pressure may be applied to the cartridge to draw the sample through the plasma separation region and into the sub channel including the cuvette.