Table 4

Best-fitted model with the best combination of clinical and laboratory variables and β-coefficients used for the calculation of the MS score

β-coefficient95% CI
Central nervous system (CNS) involvement2.441.26 to 3.65
Haemorrhagic manifestations1.540.00 to 3.05
Active arthritis−1.30−2.05 to 0.00
Platelet count (PLT), x 109/L−0.003−0.005 to −0.001
Lactic dehydrogenase (LDH), U/L0.0010.0002 to 0.002
Fibrinogen, mg/dL−0.004−0.006 to −0.002
Ferritin, ng/mL0.00010.00 to 0.0002
  • In a febrile patient with known or suspected systemic juvenile idiopathic arthritis, the diagnosis of MAS should be considered if the MS score is ≥−2.1.

  • The area under the curve of the model is 0.95. For clinical variables (CNS involvement, haemorrhagic manifestations, active arthritis), a score of 1 or 0 is placed in the formula, depending on whether the variable is present or absent, respectively. For laboratory variables, the observed values in the above-mentioned unit are included.

  • Calculation of the MS score=CNS involvement×2.44+haemorrhagic manifestations ×1.54+arthritis×(−1.30)+PLT count×(−0.003)+LDH×0.001+fibrinogen×(−0.004)+ferritin×0.0001.

  • MAS, macrophage activation syndrome; MS, MAS/sJIA.