G-CSF and IL-8 for early diagnosis of sepsis in neonates and critically ill children – safety and cost effectiveness of a new laboratory prediction model: study protocol of a randomized controlled trial [ISRCTN91123847]

Table 1 Equations for calculating post-test probabilities

Algorithm/parameters	Equations
Algorithm for sepsis
Pre-test probability_s	= prevalence of sepsis
Pre-test odds_s	= pre-test probability_s/(1 - pre-test probability_s)
Likelihood ratio_s	= exp(-8.2 + 0.85 × Ln [G-CSF_p] + 0.7 × Ln [IL-8_p])
Post-test odds_s	= likelihood ratio_s × pre-test odds_s
Post-test probability_s	= post-test odds_s/(1 + post-test odds_s)
Algorithm for pneumonia
Pre-test probability_vap	= prevalence of pneumonia
Pre-test odds_vap	= pre-test probability_vap/(1 - pre-test probability_vap)
Likelihood ratio_vap	= exp(-6.8 + 1.0 × Ln [G-CSF_t])
Post-test odds_vap	= likelihood ratio_vap × pre-test odds_vap
Post-test probability_vap	= post-test odds_vap/(1 + post-test odds_vap)

The concentrations of granulocyte colony-stimulating factor (G-CSF) and interleukin (IL)-8 used in the above equations are in pg/μl. Definitions of subscript abbreviations: p, plasma; s, sepsis; t, tracheal aspirate; vap, ventilator associated pneumonia.

ISSN: 1364-8535