Leukaemia blood test. Electrical field image of a blood sample (plasma) in a patient with leukaemia. This diagnostic test relies on a change in colour and pattern of liquid crystals in an electrical field. Plasma from a blood sample is placed on a glass slide coated with voltage-sensitive liquid crystals. An electrical current is applied through the wire at centre. Colours and patterns produced are due to voltage differences, and they indicate abnormal plasma in leukamia blood cancer. Circles show a raised red ring narrower than normal; an outer blue area is discoloured from its normal blue (high voltage) indicating leukaemia. (Photo M530/307 shows normal plasma with this technique).