What is the maximum time limit for sending intact whole blood collected in a green top tube?

The maximum time limit for sending intact whole blood collected in a green top tube is 12 hours. The green top tube contains sodium heparin as the anticoagulant, which preserves the blood sample for certain assays within this time frame. Beyond 12 hours, the integrity of the blood sample may begin to deteriorate, affecting the accuracy of laboratory results, particularly in assays that are sensitive to cellular metabolism and changes in the blood components. Therefore, it is essential to analyze or transport the blood sample within the specified time to ensure reliable diagnostic outcomes.