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Table 1 Equations for calculating post-test probabilities

From: 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]

Algorithm/parameters Equations
Algorithm for sepsis
   Pre-test probabilitys = prevalence of sepsis
   Pre-test oddss = pre-test probabilitys/(1 - pre-test probabilitys)
   Likelihood ratios = exp(-8.2 + 0.85 × Ln [G-CSFp] + 0.7 × Ln [IL-8p])
   Post-test oddss = likelihood ratios × pre-test oddss
   Post-test probabilitys = post-test oddss/(1 + post-test oddss)
Algorithm for pneumonia
   Pre-test probabilityvap = prevalence of pneumonia
   Pre-test oddsvap = pre-test probabilityvap/(1 - pre-test probabilityvap)
   Likelihood ratiovap = exp(-6.8 + 1.0 × Ln [G-CSFt])
   Post-test oddsvap = likelihood ratiovap × pre-test oddsvap
   Post-test probabilityvap = post-test oddsvap/(1 + post-test oddsvap)
  1. 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.