Is there a kidney length for which you would no longer recommend attempting a kidney biopsy due to safety concerns and lack of diagnostic yield?  

Yes. I definitely do not biopsy very small kidneys. Where you draw the line is the question. I think it is not only the size of the kidney but also the height of the patient. It may be OK to biopsy a patient with a 7.5 cm kidney who is 4 feet 8 but not OK to biopsy an 8 cm kidney in a patient who is...