U.S. flag

An official website of the United States government, Department of Justice.

DNA Amplification for Forensic Analysts


Home  |  Glossary  |  Resources  |  Help  |  Contact Us  |  Course Map

Contamination introduced in the laboratory analysis process may not be avoidable, making implementation of procedures to detect these incidences crucial. DNA profiles derived from evidentiary samples and reference samples are uploaded into CODIS and are used to associate individuals with a crime. It is imperative that laboratory procedures are in place to ensure the integrity of the data generated for these functions.

Most manufacturer's multiplexes demonstrate optimum efficiency when approximately 1ng of template DNA is analyzed for 28-30 amplification cycles.06 However, the lower limit of detection can be less than 250 pg. Most contamination events involve small quantities of DNA and therefore will be detected at lower threshold values. Laboratories establish reporting thresholds based on their validation studies. Because most contamination is below that threshold, it will not be reported; analysts should assess any allelic activity under the reporting threshold to determine if it could be from contamination.

Some additional detection processes include:

  • Assessment of controls
  • Review of batch profiles
  • Maintenance of unsourced contamination profiles
  • Establishment of reference databases

Back Forward