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Causes of sweet smelling urine include high concentrations of sugars or ketones, low urine volume, and certain dietary factors. The sudden development of a sweet or fruity odor in the urine is a cause for concern, as it indicates that something is wrong with a patient's metabolism. A doctor can take a urine sample for analysis and perform some other tests to learn more about the patient's condition and develop some treatment recommendations.
High blood sugar can cause urine to smell sweet, as the kidneys express the excess sugar in the urine to eliminate it. Diabetes is a common cause for a spike in blood sugar level, and some patients have high blood sugar that doesn't quite qualify them for a diabetes diagnosis, but could put them at risk of developing this disorder. If patients notice excessive thirst along with changes in urine odor, diabetes is a culprit they should consider.
Ketones in the urine are another potential cause. This can occur during dieting, especially radical dieting, and it is also a sign of malnutrition or starvation. These patients may have normal blood glucose levels, but still have sweet smelling urine. If patients notice changes in urine odor in conjunction with dietary changes, ketones may be the cause, and a doctor can perform a test to check on the level of these compounds.
Low urine volume can be a potential cause. When patients do not drink very much water, their urine becomes concentrated, and any odors will be more apparent. If the patient hasn't been drinking water and has been consuming lots of sweet foods like fruits and baked desserts, the urine may smell slightly sweet. This is not necessarily a cause for concern, although it can be a warning sign to drink more water to prevent dehydration and kidney damage. More dilute urine shouldn't have a sweet odor in these cases.
The other cause of sweet smelling urine is an underlying metabolic disorder. One such disorder is known as maple syrup urine disease, after the distinctive odor associated with it. If an error of metabolism is causing the change in odor, the patient will probably have other symptoms as well. In patients with maple syrup urine, for example, there are also neurological symptoms and the patient will exhibit symptoms like sweet smelling urine shortly after birth, rather than developing them later in life. Patients at risk of metabolic disorders may undergo newborn screening to check for common disorders and risk factors.