What does crenated red blood cells indicate about the urine?

Crenated red blood cells in urine signify that the cells have undergone a process of shrinkage due to a hypertonic environment. When red blood cells are exposed to fluid with higher solute concentrations than their own cytoplasm, they lose water, which leads to the crenation or distortion of their shape. This effect typically occurs when the urine is hypersthenuric, meaning it has a high specific gravity and therefore a higher concentration of solutes compared to plasma.

In such urine, the osmotic gradient draws water out of the red blood cells, causing them to appear crenated. This is an important observation in urinalysis as it can help in assessing hydration status and the concentration of solutes present in the urine. Thus, the presence of crenated red blood cells is directly indicative of a hypersthenuric condition.