Development of acute kidney injury with massive granular casts and microscopic hematuria in patients with COVID-19: two case presentations with literature review

Background Complications of acute kidney injury (AKI) are common in patients with coronavirus disease in 2019 (COVID-19). However, clinical characteristics of COVID-19-associated AKI are poorly described. We present two cases of severe COVID-19 patients with AKI. Case presentation A 77-year-old woman was suspected of having vancomycin-associated AKI, and a 45-year-old man was suspected of having heme pigment-induced AKI caused by rhabdomyolysis. The granular cast, which is known to be a valuable diagnostic tool for confirming the diagnosis of acute tubular necrosis, was detected in both patients at the onset of AKI. Interestingly, both patients also developed microscopic hematuria at the occurrence of AKI, and one patient had elevated d -dimer and low platelet levels simultaneously. Conclusions Some reports suggested that COVID-19-associated microangiopathy contributed to the kidney damage. Therefore, it is possible that our patients might have accompanied renal microangiopathy, and that this pathological background may have caused exaggerated tubular damage by vancomycin or heme pigment. The etiology of AKI in patients with COVID-19 is multifactorial. Superimposition of nephrotoxin(s) and virus-associate intra-renal microangiopathy may be a crucial trigger of kidney injury leading to severe AKI in COVID-19 patients. Therefore, in COVID-19 patients, risk factors for AKI should be taken into consideration to prevent its progression into severe AKI.