We tend not to think about our health until something feels off. Chest pain might be a sign the heart isn't functioning correctly. Breathing problems might mean the lungs aren't doing well.

But how do you know if there are problems with your kidneys, the two small yet vital organs tucked away at the back of your abdomen and just below your rib cage?

"If you wait until you feel something wrong from a kidney health standpoint, you've waited too long," warns Dr. Peter Nguyen, a nephrologist at Houston Methodist. "The symptoms of kidney disease come very late, when you're already very sick."

Ideally, the first "signs" of kidney disease are detected much earlier, through routine screening performed at your primary care doctor's office.

"People come to see me because their doctor has referred them, but they often do not understand why — they typically feel fine, 'drink plenty of water' and are usually urinating without problems," says Dr. Nguyen. "It's my job to explain what is wrong about their kidneys, why problems arise and how to prevent the situation from deteriorating."

What causes kidney disease?

The two major causes of kidney disease are:

• High blood pressure
• Diabetes

"Your kidneys are filters," says Dr. Nguyen. "Every ounce of blood in your body gets continuously filtered by your kidneys so that excess fluid, electrolytes, and waste can be removed."

Increased blood pressure causes the kidneys to face more stress as they filter blood. Having excess glucose (sugar) in your bloodstream can damage the kidneys. Being overweight can require the kidneys to work harder than usual.

"Sometimes the kidneys can no longer clean your blood effectively; other times the kidneys leak protein or blood," explains Dr. Nguyen. "This leads to a dangerous imbalance of fluids and electrolytes, as well as buildup of waste."

Dr. Nguyen likens the situation to straining spaghetti water through a colander. An effective colander holds onto the spaghetti while allowing the milky pasta water to drain through. But if the colander is damaged — its holes have clogged or worn away at the edges and become widened — either the pasta water won't drain or you lose some spaghetti.

"Very rarely do the kidneys go from normal to total failure quickly," adds Dr. Nguyen. "Chronic kidney disease is progressive injury to the kidneys over time, which is why it's so important to diagnose and intervene early."

Knowing what might put you at higher risk of kidney disease can help. As mentioned, high blood pressure and diabetes are the most prominent, but the other kidney disease risk factors include:

• Being overweight
• Smoking tobacco products
• Eating a high salt diet
• Excessive use of non-steroidal anti-inflammatory drugs (NSAIDs)

Despite having one or more of these risk factors, Dr. Nguyen notes that people with kidney problems will often say that since they drink plenty of water, their kidneys should be healthy, right?

"This is a common fallacy," adds Dr. Nguyen. "Kidney disease is not caused by not drinking enough water and drinking plenty of water doesn't prevent it either. It's of course important to stay hydrated, but in terms of keeping your kidneys healthy, it's more important to focus on controlling the risk factors."

What are the symptoms of kidney disease?

Kidney disease symptoms are nonspecific, meaning they are vague and/or things that could be caused by other health conditions or illnesses.

"Symptoms like fatigue, poor appetite and sleep disturbances occur later in kidney disease but could also be due to any number of reasons," says Dr. Nguyen. "More significant signs of kidney disease — fluid retention leading to shortness of breath or lower leg swelling — show up once the disease becomes more advanced."

One telltale sign that something is wrong with the kidneys is when they're not effectively cleaning blood. That's not something you can assess at home.

"To detect kidney disease, we need blood work and urine tests to help evaluate kidney function," says Dr. Nguyen. "A basic metabolic panel shows us your electrolyte levels and acid/base status. A urinalysis tells us whether or not you're leaking protein or blood."

These labs are routinely ordered by your primary care doctor at annual checkups.

"And this is the key. If you're seeing your doctor routinely and keeping up with recommended screenings, kidney problems will be caught early," emphasizes Dr. Nguyen. "If you're waiting for symptoms, kidney disease won't be caught until the advanced stages."

Dr. Nguyen adds the demographic that tends to struggle with this the most is men, since they often have gaps in care between the ages of 18 and 45.

"Women have opportunities such as well woman exams and pregnancy, where routine tests are performed and issues can be caught early," says Dr. Nguyen. "Men often will go years without seeing their doctor because they feel fine. But, like I said, if you wait until you feel badly, you've waited too long — which is why having a primary care doctor and being screened regularly is the most important thing."

Can kidney disease be reversed?

"Whether kidney problems are caused by high blood pressure, diabetes or being overweight, you can slow the rate of decline just by managing whatever that cause may be," says Dr. Nguyen.

What you can't reverse, however, is any kidney damage that's already occurred. The longer high blood pressure and diabetes go uncontrolled, the more likely irreversible kidney damage becomes.

"If you have very poorly controlled risk factors and the problems have gone on so long that the glomerular filtration rate is down to 15 millimeters per minute or lower, that's when people end up needing either dialysis or a kidney transplant," warns Dr. Nguyen.

For context, a normal filtration rate for a 25-year-old man is around 120 millimeters per minute.

"You can see from this that it takes quite a bit to decline to the point of needing dialysis or a transplant, which is why it's so important to see your doctor regularly and intervene early," says Dr. Nguyen. "Control blood pressure. Control blood sugar. Manage your weight. Stop smoking. All of these can slow progression of kidney disease."