Question 1 [13 marks]
Purified protein sample ‘X’ was used to plot a standard curve for an assay to measure antibodies in patients’ blood samples. Sample ‘X’ was serially diluted and absorbance was measured for each concentration (Table 1).
| Concentration of the stock solution (pg/mL) | Volume of stock solution (µL) | Volume of diluent (µL) | Final concentration (pg/mL) | Absorbance |
|---|---|---|---|---|
| 1000 | 500 | 500 | 500 | 2.504 |
| 500 | 500 | 500 | 250 | 1.607 |
| 250 | 500 | 500 | 125 | 0.982 |
| 125 | 500 | 500 | 62.5 | 0.617 |
| 62.5 | 500 | 500 | 31.25 | 0.321 |
| 31.25 | 500 | 500 | 15.62 | 0.152 |
| 15.62 | 500 | 500 | 7.81 | 0.082 |
| 0 | _ | 500 | 0 | 0 |
a) Why was ‘0’ concentration of stock solution used in this test (last row)? Justify your answer. [3 marks]
b) Using the data from Table 1, plot a standard curve. [7 marks]
c) A patient’s blood sample was diluted 100 times and it produced an absorbance reading of 0.5. What is the concentration of antibody in the patient’s blood? [3 marks]
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Question 2 [10 marks]
Test A is a gold standard method to determine disease ‘X’. Two other new test methods, B and C were compared with Test A. A method evaluation was done using Bland-Altman plots. The graphs are shown below.
a) Analyse the charts plotted and conclude if the new tests (Test B and C) are suitable to replace the gold standard (Test A). Provide relevant justifications for your conclusion. [6 marks]
Figure 1: Bland-Altman Plot showing the comparison between Test A and B
Figure 2: Bland-Altman Plot showing the comparison between Test A and C
b) It is reported that Test A has a sensitivity of 98% and specificity of 75%. Is Test A more suitable to be used as a screening test or as a confirmatory test? Justify your answer. [4 marks]
Question 3 [17 marks]
The following video shows the features of an automated slide stainer.
Laboratory XYZ, decided to purchase this slide stainer.
A. Outline the steps required to conduct a break-even analysis for these instruments. Discuss the importance of conducting break-even analysis before purchasing such devices. [4 marks].
B. State TWO analytical errors that might occur while using this instrument. Explain how to minimize them. [4 marks]
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C. Identify THREE work activities and draft a Hazard Identification and Risk Assessment (HIRA) document for the automated slide stainer. Please use the template provided below. [9 Marks]
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