Apparatus for detecting tissue oedema in a subject, the apparatus including a processing system adapted to: a) determine a measured impedance for each of a first and a second body segments, where the first and second body segments are different types of body segments; and b) determine the presence, absence or degree of tissue oedema using measured impedances for the first and second body segments wherein: determining a measured impedance for each of the first and second body segments comprises i) determining a measured impedance for each of the first and second body segments at four discrete frequencies (ω); and ii) determining values for parameters R0, R∞, τ, and α from the measured impedance values by solving the equation: Z = R ∞ + R 0 − R ∞ 1 + jωτ 1 − α for each of the body segments at the four discrete frequencies (ω), where: Z is the measured impedance at angular frequency ω, R 0 is the resistance at zero frequency; R∞ is the resistance at infinite frequency; τ is a time constant, and α has a value between 0 and 1; and wherein determining the presence, absence or degree of tissue oedema comprises: i) for each of the body segements, and using the determined parameter values for R0 and R∞, determining an index indicative of a ratio of the extra-cellular to intra-cellular fluid using the equation: I = R ∞ R 0 − R ∞ ii) calculating an index ratio based on a ratio of the first body segment index to the second body segment index; iii) determining the presence, absence or degree of tissue oedema based on the index ratio. a) determine a measured impedance for each of a first and a second body segments, where the first and second body segments are different types of body segments; and b) determine the presence, absence or degree of tissue oedema using measured impedances for the first and second body segments wherein: determining a measured impedance for each of the first and second body segments comprises i) determining a measured impedance for each of the first and second body segments at four discrete frequencies (ω); and ii) determining values for parameters R0, R∞, τ, and α from the measured impedance values by solving the equation: Z = R ∞ + R 0 − R ∞ 1 + jωτ 1 − α for each of the body segments at the four discrete frequencies (ω), where: Z is the measured impedance at angular frequency ω, R 0 is the resistance at zero frequency; R∞ is the resistance at infinite frequency; τ is a time constant, and α has a value between 0 and 1; and wherein determining the presence, absence or degree of tissue oedema comprises: i) for each of the body segements, and using the determined parameter values for R0 and R∞, determining an index indicative of a ratio of the extra-cellular to intra-cellular fluid using the equation: I = R ∞ R 0 − R ∞ ii) calculating an index ratio based on a ratio of the first body segment index to the second body segment index; iii) determining the presence, absence or degree of tissue oedema based on the index ratio. i) determining a measured impedance for each of the first and second body segments at four discrete frequencies (ω); and ii) determining values for parameters R0, R∞, τ, and α from the measured impedance values by solving the equation: Z = R ∞ + R 0 − R ∞ 1 + jωτ 1 − α for each of the body segments at the four discrete frequencies (ω), where: Z is the measured impedance at angular frequency ω, R 0 is the resistance at zero frequency; R∞ is the resistance at infinite frequency; τ is a time constant, and α has a value between 0 and 1; and wherein determining the presence, absence or degree of tissue oedema comprises: i) for each of the body segements, and using the determined parameter values for R0 and R∞, determining an index indicative of a ratio of the extra-cellular to intra-cellular fluid using the equation: I = R ∞ R 0 − R ∞ ii) calculating an index ratio based on a ratio of the first body segment index to the second body segment index; iii) determining the presence, absence or degree of tissue oedema based on the index ratio. Z is the measured impedance at angular frequency ω, R 0 is the resistance at zero frequency; R∞ is the resistance at infinite frequency; τ is a time constant, and α has a value between 0 and 1; and wherein determining the presence, absence or degree of tissue oedema comprises: i) for each of the body segements, and using the determined parameter values for R0 and R∞, determining an index indicative of a ratio of the extra-cellular to intra-cellular fluid using the equation: I = R ∞ R 0 − R ∞ ii) calculating an index ratio based on a ratio of the first body segment index to the second body segment index; iii) determining the presence, absence or degree of tissue oedema based on the index ratio. i) for each of the body segements, and using the determined parameter values for R0 and R∞, determining an index indicative of a ratio of the extra-cellular to intra-cellular fluid using the equation: I = R ∞ R 0 − R ∞ ii) calculating an index ratio based on a ratio of the first body segment index to the second body segment index; iii) determining the presence, absence or degree of tissue oedema based on the index ratio.