Diabetes is a common cause of CKD and the prevalence of diabetic nephropathy is increasing. A question that sometimes arises in the clinic is when it is appropriate to biopsy a patient with a presumptive diagnosis of diabetic nephropathy and are there any signs that may suggest that there is an alternative diagnosis. It is reassuring that recent data have suggested that renal biopsies in low-risk patients are associated with a very low risk of adverse consequences but I still don't think that anyone would recommend biopsying all patients who present with diabetes and CKD.
So how do you decide who to biopsy. It has been suggested in the past that the presence of hematuria was associated with a lower incidence of true diabetic nephropathy while diabetic retinopathy suggested the opposite. A study was recently published in the Journal of Diabetes Investigation which looked at the results of renal biopsies in patients with diabetes. In total, 55 patients with T2DM were included in the study. These were not random patients with diabetes; all of them had a clinical course which suggested that an alternative diagnosis might be present. 30 of the patients had true DN while 25 had no evidence of diabetes. Of these 13 had IgA nephropathy. One patient had a crescentic GN. The duration of diabetes was not a good predictor of the likelihood of DN. This is not altogether surprising when you consider that this is duration since diagnosis and the patients may have had diabetes for signficantly longer without being aware. Poor glycemic control and the presence of diabetic retinopathy were significantly associated with a higher likelihood of DN. No patient in the non-DN group had diabetic retinopathy which again goes to show the usefulness of this examination in stratifying patients with presumptive diabetic renal disease. This goes to show that the advice that we have been getting in the past is good - the absence of diabetic retinopathy should make you suspect an alternative diagnosis.
One interpretation of this study is that patients with atypical presentations and diabetes should have a biopsy because there is a good chance of an alternative diagnosis. Another, more conservative interpretation is that even in patients where there is a high pre-test probability of a non-diabetic lesion, the majority of patients will have diabetic nephropathy and in those that don't the treatment will most likely be the same in any case.