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How to Calculate Bias Clinical Chemistry

Utilizing the Six Sigma method of calculating bias in clinical chemistry provides highly accurate reference data to determine the degree of deviance in a method from its goal and allows researchers to decide if test outcomes yield reliable results based on whether its total error falls within the tolerable limits. This process should be applied to data yielded from a variety of clinical chemistry tests, including creatinine clearance, plasma osmolality and urea reduction ratio.

Instructions

- 1
  Assume bias is zero only under ideal conditions for a reference method if the reference is properly calibrated.
- 2
  Calculate total bias for all equations in which it is not assumed to be zero using the formula (TEag)/(CV^2x + CV^2y + CV^2z)^1/2. In this equation, TEag is the total allowable error of variable g. CV^2 is the squared value of a calculated variable, while x,y, and z represent three random variables, of which variable g is a function. In most cases, the value of the calculated variable is available for reference on control charts in the empirical results of measured controls.
- 3
  Determine the value of variable g by adding the values of calculated variables x, y, and z raised to the second power.
- 4
  Calculate the final test error percentage using the determined calculated variable values and bias in the equation Sg = (TEag - bias of g)/CVg. Sg will be the sigma performance of variable g in the test.
- 5
  Repeat the process for additional variables and determine whether the test data is reliable based on the total allowed error to sigma ratio. The total sigma of all variables must be less than total allowed error for results to be considered accurate.

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