How would you manage a patient with new renal failure and mild anemia in the setting of a moderate M-Spike and low kappa/lambda ratio, but with negative PET and bone marrow with <10% plasma cells?  

It is critical to work closely with Nephrology in these types of cases. If there is ever any doubt whether changes in renal function are a consequence of an underlying plasma cell dyscrasia, then I strongly recommend a renal biopsy. There are, of course, many other causes of renal failure and before...