Although you may not realize that your kidneys are not functioning properly, your doctor has pointed out several symptoms that may appear in the early and late stages of kidney disease.

According to the National Kidney Foundation (NKF), approximately 90% of kidney disease patients are not aware that they have kidney disease. This is a terrible statistic, but it is worth repeating.

"Most people with kidney disease don't show symptoms until late," David Goldfarb, MD, clinical director of nephrology at the New York University Lange Health Center in New York City, told Health. This is why routine screening is so important for people with risk factors for kidney disease (for example, over 60 years of age) or chronic diseases (for example, autoimmune diseases such as type 2 diabetes, hypertension, or lupus). He added that Kidney disease.

However, Staci Leisman, MD, a kidney expert at Mount Sinai Hospital in New York, told Health that there are subtle symptoms in the early and late stages. In the different stages of kidney disease, here are some things to look for.

Related: What is chronic kidney disease? The doctor explains the cause and how to treat it

Dr. Leisman said that these symptoms may appear in the first three stages of kidney disease before causing too much damage to your kidneys. (They can also appear in later stages.)

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

Dr. Lesman said that during the day, as a result of standing and sitting all day, excess fluid in your body will accumulate on your ankles and calves. But once you fall asleep at night, the excess fluid will flow directly to your kidneys. If your kidneys are damaged, they cannot filter the fluid. Dr. Leishman pointed out that the result may be more night visits to the toilet. If you get up more than once in the middle of the night, it is time to see a doctor.

When your kidneys are damaged, they cannot filter out salt, which can cause edema or swelling of your ankles, feet, and legs, says Robert Greenwell, MD, director of nephrology at Mercy Medical Center in Baltimore. You may also notice puffiness around your eyes, especially in the morning, which will not go away under normal care (think of using cold towels or tea bags). "Your kidneys are leaking protein into your urine, which means that less protein enters your blood," Dr. Greenwell explained. "Lack of protein can cause blood vessels to swell, which is usually most noticeable around your eyes."

Dr. Lesman said that one of the early signs of kidney disease is actually anemia. A healthy kidney produces 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 are not working properly, they will not produce enough EPO, Dr. Leisman explained. Therefore, you will produce fewer red blood cells. "We often see this in the middle stages of kidney disease," Dr. Lesman pointed out. If you have symptoms of anemia, such as dizziness, difficulty concentrating, abnormally pale skin, or chest pain, see your doctor. They can perform blood tests to check your hemoglobin levels, which are part of your red blood cells. Treatment is usually iron supplementation or, in very severe cases, red blood cell transplantation.

If you are diagnosed with anemia, Dr. Leisman says that it is best for your doctor to perform 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. According to the National Institute of Diabetes, Digestive, and Kidney Diseases (NIDDK), a GFR of at least 60 is considered normal, while a value below that indicates the presence of kidney disease. "When a patient's GFR reaches their 30s, we usually start to see anemia," said Dr. Leisman. In the late stages of kidney disease, you will also notice fatigue and inattention, because a sharp decline in kidney function can lead to accumulation of toxins in the blood.

If you see blood, it means you have red blood cells in your urine. Although this may be caused by UTI or kidney stones, it may also indicate kidney disease. "When your kidneys are healthy, their filters can actually prevent blood from entering your urine," explains Dr. Greenwell. However, when they are damaged, they will allow a small amount of blood to penetrate. Sometimes, you may actually see blood (usually it looks red, or it looks like tea or cola, Dr. Greenwell said). But sometimes blood is microscopic, so it can only be found through routine urinalysis, when your doctor looks at your urine sample under a microscope.

Dr. Leisman said that if you have white foam in your urine, it usually indicates a high level of albumin, which is usually low in your urine. (It is the same protein in eggs, which is why your urine will have the same foamy, egg white consistency.) "When your kidneys are damaged, one of the first things they have difficulty filtering is protein," Les Dr. Man explained.

Related: The 5 stages of kidney disease: what the nephrologist wants you to know

These symptoms usually appear in the 4th or 5th stage of the disease. They indicate that your kidneys have been so badly damaged that they can no longer filter out most of the toxins, causing them to accumulate in your blood. Unfortunately, at this point, treatment usually involves dialysis and/or eventual kidney transplantation, Dr. Greenwell said.

Your kidneys help maintain the correct balance of minerals in your bones and blood. Dr. Goldfarb said that during end-stage renal disease, your kidneys may be so severely damaged that they can't do anything. As a result, your skin may become rough and scaly, and form almost fish-like scales. According to the American Academy of Dermatology (AAD), you may notice that it feels tight and cracks easily. NIDDK points out that as your kidney function worsens, your kidneys will not be able to filter out excess mineral phosphorus and other waste products. This may accumulate in your skin and cause itching, ranging from mild annoyance to hope that you scratch your skin without causing irritation. You may scratch so hard that you have raw skin, bleeding skin, or sores. 

AAD states that over time, the accumulation of toxins in the body can cause the skin to become unhealthy pale, yellow or gray. Your skin may darken and thicken, with bumps and deep lines that look like acne or whiteheads. You may also notice an itchy rash made up of small dome-shaped bumps that sometimes join together to form rough raised patches.

AAD says that symptoms of advanced kidney disease can also appear on your fingers or toenails. The obvious signs are half of the nails, white on the top of the nail, and normal color on the bottom.

Dr. Goldfarb said that when you have kidney disease, toxins accumulate in your body, which can affect your appetite. Dr. Leisman said that about one-third of patients with end-stage renal disease also report a metallic taste in their mouths, which is most likely due to the accumulation of waste products such as urea in the body. This in turn will affect your taste buds. It may also cause nausea and vomiting.

Dr. Greenwell said that when you have severe kidney disease, you are more likely to have electrolyte imbalances, which can trigger cramps and a tingling sensation in your arms and legs. As many as 25% of people on dialysis for end-stage renal disease also have restless legs syndrome, a condition where you have an overwhelming urge to move your legs when you are resting. This is one of the reasons why 80% of people on dialysis report that they have sleep problems.

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