Discussion
In our study, we found the frequency of PGN in 45.7% of 80 diabetic patients. The frequency of NDKD has been reported between 13-82.9%3. Membranous GN was determined most common (20, 62.5%) among diabetic patients with PGN. This result showed that diabetic patients, especially membranous GN, may play a role in renal injury.
In previous studies, IgAN has been reported to be the most common GN7,12,13. However, membranous GN or other GNs have been reported to be more frequent14-19. Since kidney biopsy selection criteria vary according to clinician and center, it is difficult to determine the frequency and cause of NDKD. Many different types of GN can be seen in diabetic patients, such as membranous GN, IgAN, and FSGS.
DR, one of the DM microvascular complications, was detected in 73.6% of our DN patients, but not in PGN patients. The prevalence of DR in patients with NDKD was reported as 13.6% and 27.2%, respectively, in the previous two studies 20,21. As found in our study, the absence of DR can be a predictor of NDKD20,22. However, NDKD can be found with DR23,24. Kidney biopsy should be considered in the presence of an atypical scenario, even if a patient with DM has DR.
The median duration of DM was 11.5 years in DN patients and three years in PGN patients. The duration of DM is closely related to DN. The frequency of microalbuminuria and macroalbuminuria increases after ten years in type 1 DM25. In type 2 DM, the onset of the disease is difficult to detect, so it is recommended to investigate for DN at the time of diagnosis26. As in our study, the incidence of NDKD increased in patients with short diabetes duration27-29.
Initial serum albumin, proteinuria, fasting blood sugar, and HbA1C values were not different in DN and PGN patients. In PGN patients, proteinuria decreased in the 6th and 12th months with appropriate immunosuppressive therapy, but not in the 12th month in the DN patients.
In our study, as previously reported studies, initial proteinuria28,30 serum albumin19,31,32 serum glucose33, HbA1C28,32,34 were not different in DN and NDKD patients. Similar to Liu et al.34, our DN patients had lower serum hemoglobin levels. This result may be due to our patients with advanced CKD with DN. In our study, similar to previous studies, the mean blood pressure measurements in the two groups were not different21,35.
Median eGFR was lower in our DN group at baseline, sixth and 12th months. In addition, DN patients had more evidence of chronic renal damage on kidney biopsy. The median eGFR value decreased at 12 months in DN but did not change in PGN patients. In other words, 1-year renal survival was higher in PGN patients than in the DN group. In previous studies, 5-year renal survival was reported to be better in the NDKD group5,30. In this result, the progressive natural course of DN and the successful treatment of PGN patients with appropriate immunosuppressors may play a role.
There were some limitations in our study. These are single-center, retrospective, and insufficient numbers of patients. It is the absence of a standard and exact criteria in the indication of kidney biopsy and consists of biopsy results based on our experience.
As a result, fasting blood sugar, hbA1C, serum albumin, and proteinuria did not differ in the differential diagnosis of DN and PGN, but diabetic complications, especially DR, neuropathy, hypertension, coronary artery disease, heart failure were more characteristic in differentiation role DN from PGN. It can be thought that the frequency of PGN in DM was as much as 45 %, and the clinical course was better in patients with PGN so that the biopsy indication may be similar to that of non-diabetic patients. In a diabetic patient, PGN detection is essential due to the successful response to treatment and renal survival, then DN.