What is the minimum amount of blood commonly needed for testing for drugs?

The minimum amount of blood commonly needed for drug testing is typically in the range of 14-21 milliliters. This volume is sufficient to perform a variety of tests, including screening for multiple substances, and to ensure accurate results. Blood tests require this amount to allow for sufficient plasma or serum retrieval, which is essential for reliable analysis and to accommodate any potential retests or further analysis that may be necessary.

In practice, using a volume within this range helps laboratories efficiently process samples while maintaining the accuracy and validity of the drug testing results. The flexibility allowed by this amount is crucial in clinical and forensic settings, where precise measurements and detailed analysis are required to determine the presence of specific drugs.