Characterization of Renal Microvascular Alterations in Patients With Active Urinary Sediment and/or Proteinuria Using Ultrasound Localization Microscopy

In this study, the microvascular architecture of the kidney in adults with active urinary sediment or proteinuria is to be examined non-invasively using Ultrasound Localization Microscopy (ULM).

Kidney diseases can broadly be classified according to the affected nephron compartment into glomerular, tubular, and tubulointerstitial diseases. Glomerular diseases include, among others, the nephrotic and nephritic syndromes, which differ in their clinical and laboratory characteristics: while the nephrotic syndrome is typically characterized by marked proteinuria (>3.5 g/day), hypoalbuminemia, edema, and hyperlipidemia, the nephritic syndrome is dominated by hematuria with acanthocytes, mild to moderate proteinuria, arterial hypertension, and impaired renal function. Tubular and tubulointerstitial diseases, on the other hand, often manifest as acute kidney injury (e.g., in ischemic or toxic injury), polyuria, salt wasting, or metabolic acidosis, often accompanied by nonspecific symptoms such as fatigue or dehydration.

In addition to these classical nephron compartments, renal vascular structures may also be primarily or secondarily affected, as in vasculitis, thrombotic microangiopathies, or hypertensive nephropathy. Although these vascular structures are not directly part of the nephron, they are functionally closely linked to it and have a significant impact on renal function.

To assess kidney status, pathophysiology, and the site of injury non-invasively, urinary sediment is analyzed. Urinary sediment represents a central diagnostic tool that provides information on the localization of kidney damage, thereby functioning as a type of "liquid biopsy."

If there is clinical suspicion of acute or rapidly progressive renal failure, nephrotic syndrome, significant non-nephrotic proteinuria, glomerular hematuria, or if a systemic disease with possible renal involvement is present, a kidney biopsy is usually indicated for further diagnostic clarification. Obtaining tissue samples for histological examination is an invasive procedure associated with inpatient hospitalization, considerable burden for patients, and potential complications. Currently, alternative imaging methods cannot replace kidney biopsy. Furthermore, CT, PET, or MR imaging is associated with radiation exposure or considerable additional effort (e.g., sedation).