What does the appearance of clear red urine usually indicate?

The appearance of clear red urine usually indicates the presence of hematuria, which is the presence of blood in the urine. In cases of hematuria, red blood cells are present, giving the urine a red color, while maintaining a clear appearance because the cells do not cause turbidity unless they are in large quantities.

While the presence of pigments and hemoglobin can also contribute to red urine, clear red urine specifically highlights hematuria because hemoglobin from lysed red blood cells or pigments would typically lead to a more brownish or opaque urine appearance. Therefore, a clear red color specifically signals that blood is present without any significant breakdown products or additional substances that could cloud the urine.