A diagnostic cartridge and method of performing a diagnostic test are provided. The cartridge includes a body having a sample chamber for receipt of a sample, an analysis chamber, and a reagent-containing dispensing member. A valve member is coupled to the body for selective movement between first and second states. The valve member has a fluid passage with a hydroscopic, gas permeable vent. In the first state, the fluid passage is out of fluid communication with the sample chamber and is registered for fluid communication with the reagent-containing dispensing member. The vent prevents fluid from passing therethrough and allows air to vent therefrom as reagent flows into and fills the fluid passage. In the second state, the fluid passage remains in fluid communication with the reagent-containing dispensing member and is brought into fluid communication with the sample chamber to facilitate transporting the sample to the analysis chamber.