A coupler for indicating the presence of a substance in blood is disclosed. The coupler includes a housing and a test strip. The housing has a proximal end and a distal end, and defines a hollow interior for receiving withdrawn blood. The test strip is held within the hollow interior of the housing. The housing removably couples with a medical instrument and a needle. The test strip produces a visible signal that indicates the presence or absence of the substance in the withdrawn blood. A kit including a syringe, a needle and the coupler is also disclosed.
