Routine blood specimens can come from veins, arteries, or capillaries. Venous blood is the most commonly used specimen and venipuncture is the most common method of blood collection. Capillary blood collection is mainly used in children. At present, most of the hospital outpatient blood test specimens from the elbow vein, and the application of many years of peripheral blood collection why no longer use it? 1, routine blood reference value is mainly for venous blood. 2, the shortcomings of peripheral blood specimen volume is small, can not be repeated experiments and supplemental experiments; tissue fluid can be mixed into the local inflammation can get false results. And venous blood specimens representative of strong, no tissue fluid influence, suitable for clinical research, can repeat the experiment and additional other experiments, so for the laboratory doctors, to ensure the accuracy of test results, venous blood is undoubtedly the first choice of indicators.