Although you may not realize your kidneys aren't functioning properly, doctors point to several symptoms that can appear in the early and later stages of kidney disease.

About 90% of people with kidney disease don't realize that they have it, according to the National Kidney Foundation (NKF). It's a scary stat, but one worth repeating.

"Most people with kidney disease don't show symptoms until the very late stages," David Goldfarb, MD, clinical chief of nephrology at NYU Langone Health in New York City tells Health. This is why it's so important for people with risk factors for kidney disease, such as being over age 60, or having a chronic medical condition, such as type 2 diabetes, high blood pressure, or an autoimmune disorder like lupus, should get routinely screened for kidney disease, he adds.

But there are subtle symptoms that can show up, both in the early and later stages, Staci Leisman, MD, a kidney specialist at New York's Mount Sinai Hospital tells Health. Here are some to look for, at various stages of kidney disease.

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What are the early signs of kidney disease?

These symptoms can crop up in the first three stages of kidney disease, before too much damage has been done to your kidneys, says Dr. Leisman. (They can also show up in the later stages, too.)

If you notice any of these, see your doctor as soon as possible to check for kidney disease.

Nighttime peeing

During the day, excess fluid in your body builds up in your ankles and calves from standing and sitting all day, says Dr. Leisman. But once you go to sleep at night, that extra fluid heads straight up to your kidneys. If your kidneys are damaged, they can't filter that fluid as well. The result may be more nocturnal bathroom trips, notes Dr. Leisman. If you're getting up to go more than once in the middle of the night, it's time to pay a visit to your doctor.

Swelling

When your kidneys are damaged, they're not able to filter out salt as well, which can lead to edema, or swelling in your ankles, feet and legs, Robert Greenwell, MD, chief of nephrology at Mercy Medical Center in Baltimore, tells Health. You may also notice puffiness around your eyes, especially in the morning, which doesn't go away with usual care (think applying cold washcloths or tea bags). "Your kidneys are leaking protein into your urine, which means less goes into your blood," explains Dr. Greenwell. "The lack of protein can cause blood vessels to swell, which is often most noticeable around your eyes."

Fatigue

One of the earlier signs of kidney disease is actually anemia, says Dr. Leisman. Healthy kidneys make a hormone called erythropoietin (EPO), which sends a signal to your body's bone marrow to make more red blood cells. But if your kidneys aren't working as well as they should, they won't make enough EPO, explains Dr. Leisman. As a result, you produce fewer red blood cells. "We often see this in the middle stages of kidney disease," Dr. Leisman notes. If you have symptoms of anemia such as dizziness, trouble concentrating, unusually pale skin, or chest pain, see your doctor. They can run a blood test to check your levels of hemoglobin, which is part of your red blood cells. Treatment is usually iron supplements, or, in very severe cases, red blood cell transplantation.

If you are diagnosed with anemia, Dr. Leisman says it's a good idea for your doctor to run tests to check kidney function, such as your glomerular filtration rate (GFR). This is a blood test to check how well your kidneys filter blood. A GFR of at least 60 is considered normal, while less than that indicates kidney disease, says the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). "We usually begin seeing anemia when a patient's GFR is in the 30s," says Dr. Leisman. You will also notice fatigue and trouble concentrating in the late stages of kidney disease, since the sharp decrease in kidney function leads to a buildup of toxins in your blood.

Bloody or foamy urine

If you see blood, it means red blood cells are in your urine. While this could be caused by a UTI or kidney stone, it can also indicate kidney disease. "When your kidneys are healthy, their filters actually prevent blood from entering your urine," explains Dr. Greenwell. But when they're damaged, they allow small amounts of blood to leak in. Sometimes, you may actually see blood (it generally looks either red, or like tea or cola, says Dr. Greenwell). But sometimes the blood is microscopic, so it can only be picked up through a routine urinalysis, when your doctor looks at a sample of your pee under a microscope.

If your urine has white foam, this usually indicates high levels of albumin, a protein usually found in small amounts in your urine, says Dr. Leisman.  (It's the same protein that's in eggs, which is why your urine will have that same foamy, egg-white consistency.) "When your kidneys become damaged, one of the first things they have trouble filtering out is protein," Dr. Leisman explains.

What are the later signs of kidney disease?

These symptoms usually crop up during stage 4 or 5 of disease. They indicate that your kidneys have become so damaged that they're no longer able to filter out most toxins, leading them to build up in your bloodstream. Unfortunately, at this point, treatment usually involves dialysis and/or eventually a kidney transplant, says Dr. Greenwell.

Dry, itchy skin

Your kidneys help to keep your bones and the right balance of minerals in your blood. During end- stage kidney disease, your kidneys can become so damaged that they can't do either, says Dr. Goldfarb. As a result, your skin may become rough and scaly and develop an almost fish-like scaling. You may notice that it feels tight, and cracks easily, says the American Academy of Dermatology (AAD). As your kidney function worsens, your kidneys will stop being able to filter out waste such as excess amounts of the mineral phosphorus, notes the NIDDK. This can build up in your skin and cause itching that can range from a mild annoyance to wanting you scratch your skin off irritating. You may scratch so hard you develop raw, bleeding skin or sores. 

Over time, the build-up of toxins in your body can cause your skin to change to an unhealthy pale, yellowish or gray color, says the AAD. Your skin may darken and thicken, and develop bumps that look like pimples or whiteheads as well as deep lines. You may also notice an itchy rash of small dome-shaped bumps that sometimes join together to create rough raised patches.

Symptoms of advanced kidney disease can also show up on your fingers or toenails as well, says AAD. The telltale sign is half-and-half nails, where there's a white color on the upper part of your nails, and a normal color on the bottom part.

Loss of appetite

When you have kidney disease, toxins build up in your body, which can impact your appetite, says Dr. Goldfarb. About one-third of patients with end-stage kidney disease also report a metallic taste in their mouth, which is most likely due to the buildup of waste products in your body such as urea, says Dr. Leisman. This in turn can impact your taste buds. It can also trigger nausea and vomiting.

Muscle cramps

When you have severe kidney disease, you're more prone to electrolyte imbalances which can trigger cramping, as well as a pins and needles sensation in your arms and legs, says Dr. Greenwell. Up to 25% of people who are on dialysis for end-stage kidney disease also develop restless legs syndrome, a condition where you have an overwhelming urge to move your legs while you're resting. This is also one of the reasons why 80% of people on dialysis report that they have trouble sleeping.

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