A body fluid extraction device (1000) for extracting a body fluid and for testing a predetermined analyte or property of the fluid comprises a hollow needle (1006) having a channel (1008) linking a base end (1004) and a tip (1006) in fluid communication, a collection chamber (1010) having an input end (1012) in fluid communication with the channel, the collection chamber comprising a capillary wick (1014) configured to transport at least a fraction of the body fluid away from the input end, a testing chamber (1016) comprising a testing unit (1018) that includes a reacting material (1020) configured to react to a predetermined analyte or property of the body fluid, a solution chamber (1022), comprising a buffer solution (1024) and flow control means (1026.1, 1026.2) configured to control, a first transfer of the buffer solution from the solution chamber to the collection chamber, and a second transfer of the body fluid from the collection chamber to the testing chamber.