Chapter 11

Quality assurance and quality control (QA/QC)

What does the Z-factor describe? What is the cause of the Z-factor being too low?

You tested a water sample for its estrogenic effect but unfortunately the effect was masked by cytotoxicity at an IC10 of a relative enrichment factor REF of 10. The effect-based trigger value for estrogenicity EBT-EEQ in this bioassay is 0.34 ngE2/L. The EC10 for estradiol E2 is 3.1 ng/L. Can you be sure that the EEQ of the water sample is below the EBT-EEQ or do you need to clean up the sample to remove cytotoxic compounds and measure the estrogenic effect again?

You obtain the following raw relative light units (RLU) for estradiol (E2) in an ER transactivation assay, where you determined the activation of the estrogen receptor with 10 dilution steps of E2 in duplicate.

Log concentration E2 (ng/L) RLU RLU
2.83
2.13
1.53
0.93
0.33
-0.28
-0.88
-1.48
-2.08
-2.68
 139000
136000
131501
118000
102779
85807
76395
59000
61969
61000
 124000
128000
126185
113032
105665
81364
72881
65947
55265
57000

The unexposed control cells have a mean RLU of 57542 with a standard deviation of 2249. The Z-factor for this setup of the ER CALUX is 0.71. The equation for the Z-factor is given in Chapter 11, equation 11.4.
This ER transactivation assay is a very sensitive assay, and you need to use charcoal-stripped or dialyzed FBS (fetal bovine serum). One day you have grabbed the wrong bottle of untreated FBS, and you realize that the mean RLU of unexposed control cells rose to 97050 with a standard deviation of 2123. How does the curve look like and will this error affect the Z-factor?
Can you still use the data, or do you have to discard these experiments?
NB: The mean of the maximum effect is 128448 ± 4546 in the plot and 125100 ± 4141 after the mishap with the FBS.