Mega Doctor News
By Michael Merschel, American Heart Association News
Go ahead, get the giggles out of the way. We’re about to take a close look at urine, and in such conversations, bathroom humor is often the No. 1 byproduct.
But once you’re through, perhaps you can also relieve yourself of the notion that urine is simply material for third-grade punchlines – or simple at all.
Urine is the result of a fascinating and complex system, of which the kidneys are the star, that evolved to keep our internal systems in balance, said Dr. David Pollock, a professor of medicine at the University of Alabama at Birmingham, where he co-directs the cardio-renal physiology and medicine section.
“It’s basically what keeps your cells alive,” he said. “It maintains the internal environment of your entire body.”
Which makes understanding what’s in your pee important. And that begins with understanding how it’s made.
Urine is created in the kidneys, whose job is usually described as filtering blood. But the kidneys do much more than that, Pollock said.
“There’s a very close relationship between the heart and the kidneys,” he said.
The kidneys control how much sodium and water your body retains. That water equates to the volume of blood you carry, and the greater the volume, the higher the pressure will be.
Pollock said that makes kidneys the primary organ in charge of blood pressure. “And basically, the kidney is responsible for making sure that it doesn’t get too high.”
The kidneys control that volume by regulating sodium. When sodium is retained, blood volume goes up. The kidneys also regulate potassium, which helps limit the effects of sodium.
Both are electrolytes, and the kidneys maintain electrolytes at “very, very precise concentrations,” said Dr. Janani Rangaswami, a professor of medicine at the George Washington University School of Medicine and Health Sciences in Washington, D.C.
Those concentrations can significantly affect health, said Rangaswami, who is also chief of nephrology at the Washington VA Medical Center. Electrolyte imbalances such as low sodium level can lead to seizures. High or very low potassium could lead to heart rhythm problems.
The kidneys also balance the blood’s acidity and filter out waste products, as well as some drugs, from the bloodstream.
The result of all this balancing and filtering is urine. It flows from the kidneys through the ureters to the bladder, where it’s stored until the next commercial break, rest area or whenever it’s your turn in the bathroom.
Depending on a person’s size, the kidneys might filter around 48 gallons of blood each day, Rangaswami said. That might yield up to a couple of quarts of urine, although it’s important to not fixate on how much urine you produce, she said.
Patients sometimes get the mistaken notion that “if they don’t have a certain urine output, that’s a bad thing, which is not true,” she said. In reality, the amount can be “all over the place,” varying because of how much fluid you’re drinking, the health of your kidneys and the medications you may be taking.
The exact composition of urine can vary day to day as well, she said. But most of it – from 91% to 96% – is water.
Thousands of additional components have been identified in urine. Pollock and Rangaswami say these are the most prominent ones:
– Urea. “Your body takes the protein that you eat, it breaks it down and takes energy from it, and then you have urea left over,” Pollock said.
Urea is mostly nitrogen. It makes a good fertilizer, and bacteria break it down into ammonia. This made urine valuable in pre-industrial times for everything from tanning leather to cleaning laundry. In ancient Rome, urine was collected from public toilets, and it was taxed.
Ammonia is what makes urine smell the way it does, Pollock said.
– Electrolytes. In addition to sodium and potassium, electrolytes include chloride, magnesium and calcium. Phosphorous, another electrolyte, is what causes urine to glow under ultraviolet light.
– Uric acid. This nitrogen-based compound is created when the body breaks down food and drinks that contain chemicals called purines. Meats, seafood, beer, beans and some vegetables are high in purines. Too much uric acid can lead to kidney stones or gout.
– Creatinine. This waste product is created as muscles work and as protein is digested.
A test called UACR, which stands for urine albumin-creatinine ratio, looks for albumin, a protein that can be a warning sign of kidney disease, Rangaswami said. That, along with blood tests that look at creatinine or urea nitrogen levels, can give doctors a good idea of current kidney function and future risk for worsening kidney function.
That’s important, she said, because “kidney disease is a powerful risk enhancer for cardiovascular disease.”
Although urinalysis is as old as medicine itself – Sumerian and Babylonian physicians recorded their findings on clay tablets 6,000 years ago, and Sanskrit texts from 100 B.C. noted 20 types of urine – your urine can tell you several things even without a test.
Urine gets its yellow color from a chemical called urobilin, or urochrome. But the intensity of that color can vary depending on how much water you’ve been drinking.
“A lot of patients wrongly infer that if their urine looks concentrated, or if it’s dark yellow, that something is wrong,” Rangaswami said. “That’s just a reflection of the urine being more concentrated. And usually drinking more fluids will make it clear. So there is no reason to get concerned every time you notice a slight change in the color.”
Certain foods, such as beets and asparagus, and some medications can also cause exotic but harmless changes in the color or smell of urine, she said.
But “any blood that is visible in the urine should always prompt a medical evaluation,” Rangaswami said.
And persistent foamy urine could be a sign of too much protein in the urine. This would be a symptom to discuss with a doctor, she said, particularly for someone who is at risk for kidney disease. That would include people with diabetes, obesity or high blood pressure.
Rangaswami encouraged people to make sure their health care team is performing routine UACR tests to monitor kidney health, and to follow a doctor’s advice if they have specific conditions such as kidney stones. But for the most part, healthy urine flows naturally from healthy kidneys, and kidneys are kept healthy by the same habits that help the rest of the body.
“In terms of diet, what would generally be considered a heart-healthy diet is also a kidney-healthy diet,” she said. That would include eating less sodium and more fresh fruits, vegetables and whole grains, while backing off on heavily processed foods.
Overall, Rangaswami said, a conversation about urine is a good way to put the importance of kidney health in focus. And “anything we can do to protect and keep the kidneys healthy is going to be good for their heart as well.”
