Bloods
ABG (if low sats)
FBC (leukopenia/leukocytosis, lymphopenia, neutrophilia, thrombocytopenia)
CRP (raised if severe), U+E (may show AKI), LFT (may be abnormal),
bone, clotting (prolonged PT), lactate (may be raised),
D-dimer (raised), LDH (may be raised)
Blood cultures (-ve)