The timing of specialist referral is guided by clinical severity and the presence of end-organ damage.

Indicators of end-organ damage in patients with MM include (Quach & Prince 2019; Rajkumar et al. 2014):

• hypercalcaemia: corrected serum calcium 0.25 mmol/L above the upper limit of normal or higher than 2.75 mmol/L
• renal impairment: creatinine clearance 177 μmol/L (> 2 mg/dL)
• anaemia: haemoglobin below 100 g/L or 20 g/L below the lower limit of normal
• bone lesions: one or more osteolytic lesions on skeletal radiography, CT or positron emission tomography (PET) CT.

Patients with evidence of end-organ damage should be seen by a haematologist as soon as possible, ideally not longer than one week.

Patients without overt end-organ damage should ideally be seen by a haematologist within four weeks.

Patients with severe hypercalcaemia, renal failure, symptoms of hyperviscosity, severe new-onset back pain or acute neurological symptoms should be immediately referred to a haematologist or emergency department.