Chemouny JM, Bobot M, Sannier A, Maisons V, Jourde-Chiche N, Ferriere E, Joly D, Vigneau C, Rioux-Leclercq N, Barba C, Daniel L, Halimi J-M, Vrtovsnik F: Kidney Biopsy in Type 2 Diabetes: A Multicenter Cross-Sectional Study. American Journal of Nephrology DOI 10.1159/000514259
The role of kidney biopsy in patients with type 2 diabetes mellitus (T2DM) is constantly being re-examined. It is very clear that a fraction of patients with T2DM presenting with clinical features of CKD (diabetic kidney disease; DKD) do not have the classical findings of diabetic nephropathy (DN; a pathological diagnosis) but rather have one or the other of a myriad of non-diabetic kidney disease (NDKD) or both DN and NDKD simultaneously. Clinical differentiation of these possibilities is difficult. Thus, when NDKD is suspected, a kidney biopsy is indicated as it might change the prognosis or treatment. Kidney biopsy findings in patients with DKD therefore differ according to the indications for performing the biopsy in the first place.
Chemouny and colleagues from France report on a multi-institutional, cross-sectional study of 463 kidney biopsies in patients with T2DM. The indications for kidney biopsy fell into 7 categories: (1) recent onset of nephrotic syndrome; (2) low or rapidly declining eGFR; (3) rapid increase in proteinuria; (4) short duration of T2DM; (5) presence of hematuria; (6) absence of retinopathy, and (7) any other clinical/laboratory clue suggesting NDKD. Overall, NDKD was found in 40% of the kidney biopsies.
NDKD was found in kidney biopsies performed for indications 1, 2, 3, and 7 in 40, 24, 7, and 54% of the subjects. No kidney biopsy showed NDKD when performed for indications 4, 5, and 6. Logistic regression suggested that an eGFR <15 mL/min/1.73 m2, urine protein:creatinine ratio <300 mg/mmol, hematuria, HBA1c of <7%, and T2DM of <5 years duration were predictive of NDKD, independent of the indication used to perform the kidney biopsy. These findings suggest that rapid progression of kidney impairment or proteinuria are major clues to the presence of NDKD and that the presence of hematuria or the absence of retinopathy are not very useful in determining the likelihood of finding NDKD in a kidney biopsy in a patient with DKD. This issue was also recently examined by Sanghavi et al.  in 399 kidney biopsies in patients with DKD in a single-center study in Seattle, WA, USA. They found that retinopathy and more severe proteinuria were indicative of DN while signs of acute kidney injury were more compatible with NDKD.
Clinical differentiation of DN from NDKD in patients with DKD and T2DM remains an inexact science. Biomarkers specific for NDKD would be very helpful to add precision to what is now a very sophisticated guessing game with a few emerging rules. Because of the implications for prognosis and treatment it is probably wise to err on the side of kidney biopsy when doubt exists.
1. Sanghavi SF, et al. Histopathologic and clinical features in patients with diabetes and kidney disease. Kidney360. 2020;1:1217–25.