Abbott CELL-DYN 3200 System Operator's Manual page 548

Quality Control
Quality Control Guide
CELL-DYN 3200 Westgard
Overview
Westgard Rules
®
11-18
Rules
®
A control rule tests the control result against control limits to determine whether
the CELL-DYN 3200 shows acceptable accuracy and precision. The limits are
derived from the mean and standard deviation of control measurements obtained
when instrument performance is stable and acceptable. The most common rule
used in Hematology Quality Control is the mean ± 2SD limits. Ninety-five percent
of the control results should fall within the ± 2SD limits.
Quality control rules detect random or systematic error. Random error may be
defined as an increase in the SD (loss of precision). Systematic error may be
defined as a shift in the mean value (loss of accuracy). A multi-rule quality control
procedure combines several control rules to improve the detection of both types of
error.
Westgard recommended a multi-rule approach to evaluating quality control
results. 2 This approach has long been used in the chemistry laboratory
in the hematology laboratory. A set of modified Westgard
monitor quality control results on the CELL-DYN 3200.
NOTE: Do not use the values for mean range listed on the commercial control's
assay sheet in conjunction with Westgard
Westgard Rules with commercial controls, establish the SD for each
®
parameter on your instrument. Enter limits based on 2SDs. For Westgard
Rules, control limits are assumed to be 2SD.
The modified Westgard
®
available on the CELL-DYN 3200 are:
Rule 1 (1 ):
3s
Rule 2 (2 ):
2s
Rule 3 (R ):
4s
Rule 4 (2 of 3 ):
2s
Rule 5 (4 ):
1s
Rule 6 (10x):
Rules (Westgard's nomenclature is given in parentheses)
Value outside 3SD
A control result exceeded the mean ± 3SD
Two consecutive values outside the same 2SD
Two consecutive results fell outside 2SD on the same side
of the mean
Two consecutive values outside opposite 2SD
One result was greater than 2SD above the mean and the
next result was greater than 2SD below the mean.
Consequently, the range between the results is greater
than 4SD.
Two of three consecutive values outside same 2SD
Two of the last three results fell outside 2SD on the same
side of the mean
Four consecutive values outside same 1SD
Four consecutive results fell outside 1SD on the same side
of the mean
Ten consecutive values on the same side of mean
Ten consecutive results fell on the same side of the mean
CELL-DYN
Section 11
3 but is new
rules may be used to
®
® Rules. Before using
® 3200 System Operator's Manual
9140181H—October 2001
®