Which condition is characterized by inflammation of the kidney's filtering units?

The condition characterized by inflammation of the kidney's filtering units is glomerulonephritis. This condition specifically affects the glomeruli, which are tiny filtering units within the kidneys responsible for removing waste products from the blood while retaining essential substances like proteins and cells. When an individual has glomerulonephritis, the glomeruli become inflamed, leading to impaired kidney function and potentially resulting in symptoms such as blood in the urine, swelling, and high blood pressure.

The other conditions listed involve different aspects of kidney health. Nephrosis typically refers to a group of kidney disorders that cause nephrotic syndrome, which is characterized by high protein levels in the urine but does not specifically denote inflammation of the glomeruli. Pyelonephritis is an infection of the kidney, often affecting the renal pelvis, rather than inflammation confined to the glomeruli. Chronic kidney disease encompasses a broader spectrum of kidney damage and function decline over time and is not solely focused on the inflammatory aspect.

Thus, glomerulonephritis is the most precise answer since it directly describes the inflammation of the kidney's filtering units, aligning with the specifics of the question.