Laboratory performances vary with time. Mechanisms should be in place to identify problems (quality assurance).

The following factors could be considered in trouble shooting among others.

Personnel: Poor attitude, insufficient training, inadequate supervision.

Assay: Incorrect storage, reagents, contaminated reagents, expired assays, problem with blank values.

Sample: Contamination, microbial growth or poor quality.

Equipment: Operational problems, calibration problems, maintenance problems.