Serum glucose determinations are done on samples from a control pool each day for 30 days. Quality control statistics are then calculated.
The mean is 100 mg/dL and the standard deviation is 4 mg/dL. These statistics are used to label a quality control chart for the mean and +2 SD. Samples from the same control pool are then assayed each day along with patient samples, and control results are plotted on the chart. Results for the first 10 days are as follows:
Day Result
1 96
2 97
3 95
4 107
5 106
6 107
7 89
8 103
9 106
10 105
The coefficient of variation for these statistics is:
A) 4
B) 8
C) 12.5
D) 25
Question 2
True or false? A patient's blood urea nitrogen (BUN) was 50 mg/dL on Day 1, and the control serum for BUN was within 2 SD of the mean on that day.
On Day 2, the same patient's BUN was 70 mg/dL; again, the control value was acceptable. Should the physician interpret this increase in the BUN as a real pathologic change in the patient? (The only control level available for this test has a mean value of 20 mg/dL and a standard deviation of 2 mg/dL.)
A) True
B) False
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