You flush it down the toilet many times a day without thinking... but your pee can actually say a lot about you.

What your body has -- or hasn’t -- excreted can not only reveal whether you’re pregnant or what drugs you’ve taken; it can also clue doctors into whether you’re sick. Urine is useful to physicians because it contains everything that’s left over after your kidneys have done the important job of filtering out toxins, waste products, and excess fluid from your blood.

So, if you’ve imbibed something you shouldn’t have, or if something’s wrong with your kidneys, urine is a perfect tell-all fluid. Plus, getting a sample is as easy as going to the bathroom. And thanks to rapid urine tests, an initial check is fast and easy.

In these types of tests, you just dip a special strip of paper into some urine, and simple chemical reactions trigger a change in color. So they can tell you a number of things all at once... Like the pH of your pee, the concentration of various compounds, and its levels of certain cells or molecules, such as nitrite. (video) Normally, your urine doesn’t have any nitrite in it, although it’s chock full of nitrate.

But some bacteria produce enzymes that convert nitrate to nitrite, so extra nitrite in your pee is a sign of a bacterial infection, usually in the urinary tract. If you have an infection, you’re also likely to have more white blood cells in your urine, since your body produces lots of them to try to fight off invaders. Lots of protein, on the other hand, could be evidence of a kidney injury or kidney disease, since normally your kidney keeps proteins in your body, because they can be re-used.

And too much glucose, or sugar, could be a sign of diabetes. Now, if the results from this “dipstick test” are abnormal, doctors will sometimes spin down the urine sample, putting it in a centrifuge to separate out some of its components. Then, under a microscope, you can see if bacteria or fungi are actually there, or if there are a bunch of red or white blood cells, which could indicate bleeding or inflammation.

You can also catch some more unusual things, like groups of cells or sticky proteins that clump together called casts. These are basically molds of the insides of your kidney’s tubules, and they can be a sign of kidney disease. And then there are crystals, which come in all shapes and sizes, and can be made out of different materials.

Finding crystals in your pee might mean you’re prone to kidney stones, or are experiencing a dangerous side effect of chemotherapy, or have even have ingested something toxic, like antifreeze. While it’s rare for urine by itself to provide a definitive diagnosis, it’s a great starting point, and doctors can often spot problems early on, often before you have any symptoms. So, peeing into a cup at the doctor’s office may not be your favorite part of your regular check-up, but for doctors, that little sample is pure gold!

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