Introduction: Isolated microscopic hematuria (IMH) is frequently encountered in potential kidney donors and often prompts the consideration of kidney biopsy to exclude underlying glomerular disease when other etiologies are not apparent. However, defining IMH presents significant challenges exacerbated by conflicting guidelines. While the British Transplantation Society advocates for dipstick testing alone, KDIGO guidelines stipulate that positive dipstick results alone are inadequate to define IMH, necessitating confirmation through urine microscopy. However, manual microscopic testing is labor-intensive, time-consuming, and prone to inaccuracies, leading to a growing reliance on automated analyzers. Yet, these analyzers may yield false-negative results, potentially due to their inability to recognize dysmorphic red cells, unlike normal red cells. Consequently, the decision whether to perform kidney biopsy solely based on the detection of hematuria or on the presence of red cells in urine microscopy remains ambiguous.
In response to these challenges, our institution has adapted its practice over time, now routinely performing kidney biopsies on most potential donors exhibiting positive urinalysis for blood, regardless of urine microscopy findings. Biopsy is offered when persistent hematuria lacks explanation.
This study aimed to correlate kidney biopsy findings with urinalysis results to better inform clinical decision-making.
Methods: We conducted a retrospective analysis of data from potential kidney donors who underwent kidney biopsies between January 2015 to February 2024. Urine specimens from each individual were analyzed using the Cobas® 6500 urine analyzer on at least two occasions. Urine microscopy was considered negative if the analyzer reported 0-5 red blood cells. Kidney biopsy was performed if urinalysis indicated >1+ blood, even in cases where microscopy for red cells was negative. All biopsy specimens underwent histological examination with hematoxylin and eosin (H&E) staining, immunofluorescence, and electron microscopy.
Results: A total of 272 individuals underwent kidney biopsy. Histopathological abnormalities were detected in 62% of cases, with thin basement membrane disease being the most common (40%), followed by IgA nephropathy (16%), and other lesions (2%). Notably, even among patients with negative urine microscopy for red cells, 58% exhibited histopathological abnormalities. Alarmingly, almost half (20/43) of patients diagnosed with IgA nephropathy had negative urine microscopy for red cells.
Conclusion: Our study highlights that potential kidney donors may harbor significant glomerular disease, including IgA nephropathy, even in the absence of red cells detected by urine microscopy. Therefore, once persistent hematuria is confirmed, kidney biopsy should be offered before acceptance for kidney donation.