A detection device for detecting a blood count parameter in a blood vessel, comprising a transmitter to inject a first transmit signal of a first frequency into the blood vessel and a second transmit signal of a second frequency into the blood vessel, a receiver to receive a first receive signal at the first frequency and a second receive signal at the second frequency, a loss detector to determine a first loss value on the basis of the first transmit signal and the first receive signal at the first frequency, and to determine a second loss value on the basis of the second transmit signal and the second receive signal at the second frequency, and a processor to determine a first frequency shift of the first loss value relative to a first reference loss value, determine a second frequency shift of the second loss value relative to a second reference loss value, and determine the blood count parameter on the basis of the first frequency shift and the second frequency shift.