25 | 24 Heparinised SF | 3 Laboratories compared with an expert “reference laboratory” | Comparing the 3 “test” laboratories with the reference laboratory. In one or more of the test laboratories, the %PMN cells in 12/24 SF samples fell outside (2SD) of the 95% confidence limits of the value determined by the reference laboratory (Correlation coefficients for %PMN cell findings in 3 laboratories compared with the reference laboratory were 0.73, 0.84, 0.94. respectively) | Variable Occasional wide variation in results and misidentification of cells |
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25 | 24 Heparinised SF | Reference laboratory only Intralaboratory study 2 Observers | The mean %PMN cells counted by 2 observers were similar—maximum difference of 25%. When a 2 sided significance test for difference from previous value was applied, 23/24 percentages were within 95% confidence interval | Good |
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24 | 1 | 26 Hospital laboratories | The percentage of PMN cells identified varied from 0 to 30%, mean 13.8 (SD 8.6) (median 11%) | Considerable variation |