Total Allowable Error

 

Variables

 

laboratory mean =

= mean at laboratory for period of stability in reagents & controls

 

"true" mean =

= mean for all methods & laboratories

 

laboratory standard deviation =

= standard deviation noted at laboratory

 

method standard deviation =

= standard deviation reported by vendor

 

CLIA limit

(1) given as a range, either using a percent or an absolute value

(2) if both specified, use whichever is greater

 

Calculations

 

calculated bias =

= laboratory's deviation (based on site and method) from mean of all sites =

= ((laboratory mean) - (true mean))

 

laboratory imprecision =

= (factor) * (laboratory standard deviation)

 

where:

• factor is 1.96 for 95%

• factor is 2.50 for 99%

 

Total allowable error = TE _a =

= ((CLIA limit) * (true mean))

 

bias as percent of CLIA limit =

= ((calculated bias) / ((CLIA limit) * (true mean))) =

= (((laboratory mean) - (true mean)) / (total allowable error)) =

= ( ((laboratory mean) - (true mean)) / ((CLIA limit) * (true mean)))

 

total error =

= calculated bias + imprecision =

= (((laboratory mean) - (true mean)) + (laboratory imprecision))

= ( ((laboratory mean) - (true mean)) + ((factor) * (laboratory standard deviation)))

 

assessment of performance =

= (total error) / (total allowable error) * 100 =

= (((laboratory mean) - (true mean))+ (laboratory imprecision)) / (((CLIA limit) * (true mean)))* 100 =

= (((laboratory mean) - (true mean))+ (1.96 * (laboratory standard deviation))) / (((CLIA limit) * (true mean))) * 100

 

systemic error (critical) = SE _c =

= ( ( ( (total allowable error) - (calculated bias) ) / (laboratory standard deviation) ) - 1.65) =

= ( ( ( ((CLIA limit) * (true mean)) - ((laboratory mean) - (true mean))) / (laboratory standard deviation)) - 1.65)

 

Use the systemic error for selection of QC control rules to use

 

standard deviation to use =

= ((calculated standard deviation) * ((denominator of primary rule) / 2))

 

Example: If using 1:3s rule, where the denominator = 3

 

standard deviation to use =

= (laboratory standard deviation) * (3 / 2) = 1.5 * (laboratory standard deviation)