systematic error

systematic error

1. constant or proportional error of set pattern

   • constant: test results are consistently higher (or lower), by the same amount, than the true value
     • possible cause: interference inherent in the sample is measured along with the constituent being tested
   • proportional: test results are consistently higher (or lower) than the true value by the same percentage

2. can be ignored if:

   • small
   • constant w/ every sample patient analysed
   • incorporated into the reference interval
     • eg: in the determination of creatinine applying Jaffe reactio, non creatinine chromogens r measured with creatinine. non-creatinine chromogen r relatively constant in all pts, & so the average conc. of non-creatinine chromogens is incorporated into the reference interval

3. assessment of systematic error

   • 1. recovery studies
     • helpful in assessing systematic proportional error (%)
   • 2. interference studies
     • can be used to assess constant systematic error (value)
   • 3. comparison studies
     • can be used to assess both constant & proportional error