Self use kit for providing blood samples for use in measuring glomerular filtration rate

A self-use kit for providing blood samples for use in measuring the glomerular filtration rate of a patient, said kit comprising: a container that is adapted to be sent by post; one or more pieces of absorbent substrate of a quality and consistency suitable for the collection of blood spots for diagnostic analysis; and a timer comprising a user-operable actuator, recording means for recording the time the or each time the actuator is operated, and means for extracting said time or times from the timer; whereby a patient obtains one or more timed samples of capillary blood after being intravenously injected at a known time with a filtration marker, collecting a blood spot on the or a respective one of said pieces of absorbent substrate, and actuating said actuator upon obtaining the or each sample to record the time of the or each sample; whereafter the piece or pieces of absorbent substrate and the timer may be packaged in the container and sent by post to a laboratory for analysis of the timed blood samples to determine the rate of clearance of the filtration marker.