A5V4d

Table 11.10 Additional cost per additional correct diagnosis detected of PCT over CRP
Investigation Cost Effectiveness
(correct
diagnoses)
CRP £1,500 790
Incremental
cost
(additional
cost of PCT
over CRP)
Incremental
effectiveness
(additional
correct
diagnosis)
Health economics
Additional
cost per
additional
correct
diagnosis
PCT £9,000 750 £17,500 −41 Dominated
(more costly,
less effective)
CRP C-reactive protein, PCT procalcitonin
Sensitivity analysis
Both one-way and two-way sensitivity analyses were undertaken. One-way sensitivity analysis
involves altering the value of a single parameter while holding all the others constant, to determine
how robust the conclusion is to the values used in the model. Two-way sensitivity analysis means that
two parameters are changed simultaneously.
1. Varying the prevalence of SBI in the population
Given that there is lack of published evidence with regard to the prevalence of SBI for the febrile
children, sensitivity analysis was conducted by varying the levels of prevalence in order to assess the
extent to which the final results are dependent on change in this parameter. CRP dominated PCT until
the prevalence reached 27% in the population. However, the additional cost per additional correct
diagnosis was £5,769.
2. Diagnostic accuracy of CRP and PCT
Sensitivity analysis was conducted by using various estimates of the diagnostic accuracy of the tests.
Data from an older study conducted by the same authors245 was inputted into the cost analysis.
Table 11.11 shows that, using different data for diagnostic accuracy, the additional cost per additional
correct diagnosis by switching from using CRP to PCT to detect SBI may be up to £246 per test.
Table 11.11 Results of sensitivity analysis using levels of diagnostic accuracy from the second study 245
Investigation Cost Effectiveness
(correct
diagnoses)
CRP £1,500 757
Incremental
cost
(additional
cost of PCT
over CRP)
Incremental
effectiveness
(additional
correct
diagnosis)
PCT £9,000 788 £7,500 31 £246
CRP C-reactive protein, PCT procalcitonin
3. Sensitivity of the diagnostic tests
Additional
cost per
additional
correct
diagnosis
One-way sensitivity analysis was conducted to test the robustness of the final results by varying the
levels of sensitivity of the tests only. CRP still dominated PCT when the level of sensitivity for PCT
was increased to 1.00 (maximum). Also, CRP still dominated PCT even after decreasing significantly
the level for CRP. This means that the CRP was still more cost-effective than PCT even when
changing only the levels of sensitivity of PCT and CRP.
4. Specificity of the diagnostic tests
Sensitivity analysis was undertaken to check the robustness of the results with regard to the levels of
specificity. The final results were sensitive to the level of specificity of the tests. By increasing the
level of specificity from 0.74 to 0.79, the PCT became more effective than CRP. However, the
additional cost per additional correct diagnosis was £1,071 per test.
255