What level of 24h urine M protein do you consider to define active myeloma in a patient with renal insufficiency, proteinuria and monoclonal gammopathy?   

When in doubt, a renal biopsy is preferred to define what is the exact disease process leading to renal dysfunction. If cast nephropathy is seen, this supports a diagnosis of myeloma. If amyloid or light chain deposition disease is seen, this also supports a diagnosis of amyloidosis or MGRS/myeloma,...