- Incorrect and variable pipetting and dispensing.
- Inadequate mixing of sample with reagents.
- Samples are not incubated consistently at the correct temperature (when incubation of tests is required).
- Individual items of glassware or plastic-ware are not clean or dry before reuse.
- Equipment malfunctioning (erratic performance).
- Incomplete removal of interfering substances, e.g. red cells when measuring analytes in serum or plasma.