What can cause urine to appear dark yellow or amber?

The appearance of urine as dark yellow or amber is primarily associated with dehydration and the presence of excess bilirubin. When a person is dehydrated, the concentration of waste products in the urine increases, leading to a darker color due to higher levels of urobilin, a byproduct of bilirubin breakdown. Additionally, if there is an increase in bilirubin itself due to liver dysfunction or biliary obstruction, the urine can take on a dark amber hue.

Dehydration significantly affects urine concentration, reducing the amount of water and increasing the concentration of solutes, which directly correlates to color intensity. Similarly, the presence of excess bilirubin, which can occur in conditions related to liver disease, hemolysis, or bile duct obstruction, also contributes to urine coloration.

While excessive hydration typically results in lighter-colored urine due to dilution of the solutes, and protein presence might lead to other changes such as foaminess rather than color changes, the key factors for dark yellow or amber urine are dehydration and excess bilirubin.