Step One

If contamination is suspected, the first step of the investigation should be to determine where the contaminant profile has arisen.  In many cases, it can be traced back to a particular step in the analysis by working backwards in a step-by-step process.  

It is important to compare the contaminant profiles to:

• Other samples from the same batch
• Samples from other batches processed in the same time frame
• Staff profiles
• Previously detected contaminant profiles
• Other persons involved in the collection and handling of the evidence

If the profile contains too few alleles to effectively screen against the above, consideration can be given to boosting the signal strength by using one or more of the following:

• Amplifying additional extract
• Extending the injection time
• Concentrating the extract or amplicon
• Increasing the number of PCR cycles

These troubleshooting procedures should not be used for processing, interpreting, or reporting samples unless validated by the laboratory.

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