Sodium, Potassium, and Phosphorus: Why They Matter in Kidney Disease

The kidneys have a remarkable ability to keep the body in balance. While they are best known for their ability to filter blood and remove waste and excess fluid from the body, they also regulate several minerals that are essential to everyday function, including sodium, potassium, and phosphorus. 

When kidney function declines, their ability to regulate these minerals becomes less precise, often resulting in imbalances that can adversely affect health. Understanding how these nutrients work and why they matter in chronic kidney disease (CKD) can enable patients to make choices that support their well-being.

How the Kidneys Regulate Sodium, Potassium, and Phosphorus

Each of these minerals plays a distinct role in the body. Sodium helps regulate fluid balance and plays a role in blood pressure management. Under healthy conditions, the kidneys respond to sodium levels and hormonal signals that dictate when and how much water to excrete in the urine. When this function is impaired, the body tends to retain fluid, which can increase blood pressure and place additional strain on the heart and kidneys.

The kidneys also play a vital role in keeping potassium levels in the blood within a normal range. In advanced stages of CKD, the ability to eliminate potassium from the body declines, often leading to a rise in potassium levels in the blood (a condition known as hyperkalemia). Because potassium levels directly impact the electrical activity of the heart, hyperkalemia increases the risk of life-threatening arrhythmias. 

Phosphorus works closely with calcium to build strong bones and support energy production. High phosphorus levels (a condition known as hyperphosphatemia) can weaken bones and contribute to harmful calcium-phosphate deposits in blood vessels and soft tissues. These deposits increase cardiovascular risk, a serious and often underrecognized issue for people living with CKD.

Why CKD Impairs Normal Body Functions

As CKD advances, many hormonal changes take place, which can affect mineral levels in the body as well as other body functions. These include changes to the renin-angiotensin-aldosterone system, a hormonal system that makes it more difficult to control blood pressure in advanced CKD stages. Changes to vitamin D and parathyroid hormone pathways also occur, disrupting how the body handles calcium and phosphorus and predisposing individuals to bone disease. In addition to impacts on body minerals, a decrease in erythropoietin production, a hormone necessary to make healthy red blood cells, also occurs, predisposing patients with advanced CKD to anemia. Lastly, the kidneys lose their ability to keep acid and base levels in the body within normal ranges, typically resulting in overly acidic blood, which can be harmful. 

These hormonal and mineral changes are subtle and not usually associated with noticeable symptoms, but they can lead to significant health risks over time. For example, while some individuals with hyperkalemia may note muscle weakness or fatigue, many people do not experience any symptoms. Since hyperkalemia can cause dangerous heart rhythms, it is important for potassium levels to be monitored regularly. 

Similar to hyperkalemia, hyperphosphatemia is largely asymptomatic. Over time, chronically elevated phosphorus levels can weaken bones and increase the risk of bone fractures. It also contributes to vascular calcification, which increases risk of cardiovascular events. Because these changes happen silently over time, routine monitoring is critical. 

What Is “Normal” in CKD?

It is normal for sodium, potassium, and phosphorus levels to vary from patient to patient. Reference ranges provided on laboratory reports typically display the range of values considered normal for most healthy people. Example ranges are shown below for sodium, potassium, and phosphorus. 

*Ranges may vary per laboratory

Patients with advanced CKD are more likely to experience mineral levels outside of a normal range. In addition, certain medications used to treat CKD impact mineral levels, particularly potassium. These beneficial medications include angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), and mineralocorticoid receptor antagonists (MRAs). Repeating kidney-related blood tests over time helps providers adjust therapy or recommendations based on how test results change.

What Patients Should Know

Regular lab testing is essential, especially in advanced CKD. Keeping track of minerals (like sodium, potassium, phosphorus, and calcium) and hormones (like parathyroid hormone and vitamin D) helps identify imbalances early so they can be addressed before they lead to health problems.

Diet plays an important role in keeping mineral levels in check.

• Adopting a diet low in sodium is important. Preparing meals at home, choosing products with lower sodium content, and being aware of hidden salt in packaged foods, sauces, and condiments helps control blood pressure and reduces strain on the kidneys. Healthmap Solutions (Healthmap) offers a helpful guide to lowering sodium intake for patients who may need to consume less sodium.
• When potassium levels are elevated, learning to limit high-potassium foods (such as potassium-based salt substitutes, bananas, tomatoes, oranges, potatoes) and replacing them with foods that are lower in potassium (such as grapes, apples, plums, or kale) is helpful. Healthmap’s guide to reading food labels recommends looking for foods that have less than 200 milligrams of potassium per serving for patients who have been directed to limit their potassium intake. Learning to remove potassium from vegetables is another helpful trick. Generally, this is an area where personalized guidance from a dietitian or care team is especially helpful. 
• Phosphorus management requires similar attention. Unlike the natural phosphorus found in foods like dairy products, nuts, beans, and whole grains, phosphorus-containing additives commonly used in processed foods (e.g., sodium phosphate, phosphoric acid) are more readily absorbed by the body and can quickly raise levels. Some patients may also require a prescription for phosphate binders, medications that help reduce phosphorus absorption.

Coordinated care is essential. Nephrologists, primary care providers, dietitians, and Healthmap Care Navigators can help patients interpret lab results, make practical dietary changes, and adjust medications when necessary.

Healthmap’s multidisciplinary Care Navigation team helps patients stay on track with their treatment plan and offers health education, dietary guidance by registered dietitians, support with overcoming barriers to care, and individualized coaching and guidance. Simultaneously, Healthmap works closely with providers to help coordinate care and provide timely alerts to ensure regular lab tracking is occurring.

The Bottom Line

The kidneys play the central role in keeping various minerals and hormones in balance. When kidney function declines, even small imbalances can lead to health risks. 

By monitoring lab values, adopting kidney-friendly eating habits, taking medications as prescribed, and working closely with their care team, patients can protect their health and slow the progression of CKD.