In what circumstances would you give G-CSF to a patient with severe neutropenia and HLH?

I am not aware of any direct clinical evidence that addresses this question. That said, I would be very reluctant to treat with G-CSF in the setting of HLH. G-CSF is an inflammatory cytokine that might aggravate HLH. Moreover, since the mechanism of neutropenia in HLH is thought to be increased neutrophil destruction, the impact of G-CSF to improve neutropenia is uncertain.