A5V4d

Health economics
11.4 Economic evaluation of C-reactive protein versus
procalcitonin – analysis undertaken for the 2007 guideline
Fever without localising signs in young children remains a diagnostic problem. There is evidence that
procalcitonin (PCT) may be more effective in terms of sensitivity than commonly used C-reactive
protein (CRP). However, the evidence on diagnostic accuracy is not robust. An economic evaluation
approach was adopted to assess the cost-effectiveness of using different estimates of specificity and
sensitivity of these tests from the published data.
A simple decision-analytic model was constructed which incorporated both the sensitivity and
specificity of each test. Additional correct diagnosis was the outcome used. The model is based on
limited information on PCT in children with fever without apparent source (FWS) and in other
situations PCT may perform better than CRP.
Figure 11.2 is a schematic representation of the decision tree used in the analysis. Before investigations,
febrile children were assumed to have one of two health states: either with no serious
bacterial illness (SBI) or with SBI. After the investigations, febrile children were assigned a true
positive or negative diagnosis, or a false positive or negative diagnosis. The model covers only the
initial diagnosis and not the cost of treatment of SBI. The term SBI for this guideline includes seven
potential types of serious infection. Each type of infection would require a different pathway. The
description of this pathway and its potential outcomes was beyond the scope of this guideline.
Figure 11.2 Cost-effectiveness of PCT versus CRP decision tree
Methods
Clinical effectiveness
‘Correct diagnosis’ was identified as the outcome of the analysis. This can take into account both
sensitivity and specificity in order to derive the precise levels of correctly diagnosed cases for each
type of investigation.
Correct diagnosis = true positive + true negative diagnosis
Data used in the model
Diagnostic accuracy
Estimates of the diagnostic accuracy are taken from the systematic review of the clinical evidence
presented in this guideline. Specifically, there are two studies which provide clinical effectiveness for
the model. Table 11.7 summarises the data on diagnostic accuracy of PCT and CRP presented in
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