Method of calibrating the sample height in a sample analyzer

A method for calibrating the sample height of a sample in a chamber of a sample analyzer held within an imaging optical scanning instrument, said method comprising:

• a) providing said chamber for receiving a sample, in said sample analyzer;
• b) depositing a sample into said chamber wherein said sample contains a fluorescent dye;
• c) illuminating said sample with excitation light;
• d) scanning the sample with said instrument to detect the fluorescence from said sample;
• e) measuring fluorescence intensity values as a function of the focal plane position of the instrument relative to the sample;
• f) determining a characteristic width of the fluorescence intensity vs. focal plane position curve;
• g) calculating an approximate sample height from said characteristic width;
• h) calculating a corrected sample height value by taking into account the index of refraction of the sample;
• and
• i) obtaining the calibrated sample height.