Laboratory data illustrative of preanalytical errors such as the effect of improper storage of sample, the type and concentration of anticoagulant used for specimen collection, the lability of an improperly preserved sample, and the effect of infusion are presented. Strategies to detect preanalytical errors by delta checks are illustrated. Physiological variables such as the effect of age, sex, diet, smoking, menstrual cycle, pregnancy, and specimen collection variables such as posture, duration of tourniquet application, diurnal effects and exercise introducing preanalytical error are discussed. The types of post analytical errors ranging from improper entry of data to errors in strategies used for the interpretation of laboratory data are also highlighted.