An apparatus comprising: a body having a cavity with a wall to receive a sample of blood obtained from a patient for testing; a displacement member movably received on the body, the displacement member movable through a distance on the body from a first position to a second position; a spring element connected intermediate the displacement member and the body to bias the displacement member against movement from the first position; and an indicator having a signal generator, a first portion (26, 28) on the body and a second portion on the displacement member, the second portion of the indicator being at least one of engaged with and aligned with the first portion of the indicator with the displacement member in the second position to produce a signal from the signal generator indicating movement of the displacement member to the second position; characterised in that the displacement member has a wetted portion thereon forming a wall portion that, together with the wall of the cavity, is arranged to surround a blood sample introduced into the cavity, such that the introduction of the blood sample into the cavity of the body causes the blood sample to clot and to adhere to the wetted portion of the displacement member as it contracts within the cavity thereby resulting in displacement of the displacement member towards the second position; and wherein the indicator is arranged such that the at least one of engagement and alignment of the second portion of the indicator on the displacement member with the first portion of the indicator on the body produces a signal indicating whether the blood sample has a predetermined clotting capacity. a body having a cavity with a wall to receive a sample of blood obtained from a patient for testing; a displacement member movably received on the body, the displacement member movable through a distance on the body from a first position to a second position; a spring element connected intermediate the displacement member and the body to bias the displacement member against movement from the first position; and an indicator having a signal generator, a first portion (26, 28) on the body and a second portion on the displacement member, the second portion of the indicator being at least one of engaged with and aligned with the first portion of the indicator with the displacement member in the second position to produce a signal from the signal generator indicating movement of the displacement member to the second position; characterised in that the displacement member has a wetted portion thereon forming a wall portion that, together with the wall of the cavity, is arranged to surround a blood sample introduced into the cavity, such that the introduction of the blood sample into the cavity of the body causes the blood sample to clot and to adhere to the wetted portion of the displacement member as it contracts within the cavity thereby resulting in displacement of the displacement member towards the second position; and wherein the indicator is arranged such that the at least one of engagement and alignment of the second portion of the indicator on the displacement member with the first portion of the indicator on the body produces a signal indicating whether the blood sample has a predetermined clotting capacity.