How do you discuss harms of MGUS screening with other medical providers?

I understand the intent of the question, but - as always - real life is more complicated. I agree that the evidence for screening completely healthy patients for MGUS does not currently exist. But, for patients with unexplained pertinent lab/imaging findings or symptoms, it's not unreasonable.

In the example given of longstanding CKD that hasn't changed recently, I agree that this is unlikely to be AL amyloidosis primarily because AL amyloidosis is extremely rare overall. However, I have helped make this diagnosis in several patients because their PCP had checked serum free light chains as part of the workup - it's worth noting that these patients can have longstanding proteinuria without an elevated creatinine at first.

I'll also note the ...

I agree with @Dr. First Last's wonderful answer here. The challenge is that most patients who come to see us have already had these tests performed. The bigger issue is that most non-hematologists ordering them do not know how to interpret them either.

Most of the time, in my experience, screening is done not out of curiosity but because of a particular symptom or comorbid condition: neuropathy, cardiomyopathy, macroglossia, periorbital purpura, nephrotic syndrome. These are all quite reasonable.

Things that drive me a little nuts: sending haphazard SPEP/IFIX/sFLC in the very old (>90 years old), osteoporosis, and generalized arthralgias, among some others.

On a related note, I recently became aware through an ASH abstract (Ganguli et al., ...