Examples: Not enough DNA in the sample (this normally comes from the White Blood Cells), the primers used in a PCR test (amplifying the DNA) do not bind properl

Examples: Not enough DNA in the sample (this normally comes from the White Blood Cells), the primers used in a PCR test (amplifying the DNA) do not bind properly, other markers for various tests don't bind correctly, etc. Not-binding correctly could be a problem with the whole sample (ie something in the blood is throwing off the test, outside contamination by a bad draw, not documenting draw date properly and sample is expired). With solid tissue samples (often embedded in paraffin wax), there can be extensive problems with the sample being prepared incorrectly. These are normally prepared on-site at your doctor's office and there is a surprising amount of variation.