Kidney Health 101: Making Sense of Kidney Tests and Lab Results

Living with chronic kidney disease can feel like learning a new language. There are a lot of tests, and the results may leave you scratching your head. Don’t worry. NKF is here with Andy Thompson, a nephrology physician assistant, to help you decode your lab values and navigate your kidney health.

The kidneys are important organs that help keep the body balanced by removing waste and excess water. They also help regulate minerals or vitamins, make red blood cells, maintain blood pressure, and keep bones strong.

Everyone should get a basic or comprehensive metabolic blood test once a year. This allows you to understand your overall and kidney health better. Your healthcare practitioner may order urine or imaging tests if anything seems amiss.

Those with a family history of kidney disease, a childhood kidney issue, or risk factors for kidney disease should let their healthcare practitioner know and ask for frequent testing.

“High blood pressure and diabetes are the two top causes of kidney disease or kidney failure. If you have either, I recommend getting your creatinine tested at least once a year,” said Thompson. “It's crucial to make sure these diseases are not damaging the kidneys on a chronic basis.”

Are you at risk of kidney disease? Take this one-minute quiz to find out.

eGFR estimates what percentage of kidney function you have. Think of it as a snapshot of how well the kidneys filter blood.

“eGFR is found by using an equation that takes factors like blood creatinine, weight, sex, and height into account,” Thompson said. “An eGFR of 90 or higher is in the normal range. 60 or below may indicate kidney disease.”

Learn more about eGFR.

Creatinine is a waste product the kidneys help filter out. Elevated creatinine levels may suggest issues with the kidneys.

“Creatinine is a metabolic waste product that your muscles make on a daily basis,” said Thompson. “You also ingest it when you eat certain foods like red meat.”

Learn more about creatinine. 

BUN measures the amount of nitrogen in your blood, a waste product formed by the body breaking protein down.

“Your BUN can’t be used alone to determine if you have kidney disease. It is influenced by age and what we eat and drink,” Thompson said. “BUN can provide additional context about kidney function. We can also use the BUN in correlation with the creatinine to give an oversimplified estimation of someone’s fluid status.”

The kidneys help keep the body’s balance of electrolytes. Too much or too little of these essential vitamins and minerals can lead to serious health issues.

“Generally, the healthier kidneys are, the better they are regulating electrolytes like sodium, potassium, calcium, and phosphorus,” said Thompson. “The balance of electrolytes is crucial to someone’s overall health.”

• Sodium (salt): Helps the body regulate fluid. Healthy kidneys filter out excess salt. Too much salt or improperly working kidneys could cause issues like high blood pressure, damaging the kidneys further. Others with late-stage kidney disease may struggle with hyponatremia or low sodium levels in the blood.

“The big tip for most people with kidney disease is to watch your salt intake. Start by limiting foods with added salt like processed foods,” Thompson said. “Spices and herbs are great but be careful with salt substitutes. Many have potassium chloride. Check the label and pass on it if you are watching your potassium.”

Learn more about sodium.

• Potassium: Helps the nerves, muscles, and heart body work properly. Having too much or too little potassium in the blood could cause life-threatening issues like a heart attack.

“The kidneys play a critical role in potassium regulation, about 90 to 95%. Another 5% to 10% is controlled by your colon,” said Thompson. “Diet used to be the front-line treatment. Now we have potassium binders or medications that help bind potassium in the GI tract. It’s removed when you go to the bathroom so the body doesn’t absorb it. Diuretics can be used to tell the kidneys to get rid of more potassium.”

Learn more about potassium.

• Serum calcium: Helps keep bones strong and muscle movement. The body moves some from bones to the blood to maintain healthy levels. Studies have found that those with low serum calcium reach kidney failure faster.

Learn more about serum calcium.

• Phosphorus: Helps keep your bones strong. Too much phosphorus can weaken your bones by pulling calcium out of them. It can also cause harmful deposits in blood vessels and organs. This can increase the risk of heart attack, stroke, or even death.

Learn more about phosphorus.

• Serum carbon dioxide (CO2): Plays a role in regulating blood pH.  

“If kidneys aren't working, metabolic waste products, byproducts of being alive, build up in the body," Thompson said. "High CO2 levels tell practitioners the blood is acidic and indicate that the kidneys aren't doing their jobs."

Learn more about balancing the body's pH. 

Cystatin C is a protein produced by the body’s cells. Healthy kidneys filter excess out. High levels indicate kidney issues. It’s sometimes used alongside creatinine to provide a more accurate assessment of kidney health, especially in cases where creatinine levels may be misleading due to high muscle mass or other factors.

"If a healthy individual who works out, eats well, and has high muscle mass comes in with elevated creatinine levels, they may not have kidney disease,” Thompson said. “Since creatinine is a waste product produced by muscle metabolism, individuals with higher muscle mass may have higher creatinine levels. Using cystatin C in conjunction with creatinine gives us a clearer picture of kidney health."

Learn more about cystatin C. 

Proteins like albumin are usually retained in the blood by healthy kidneys. Damaged kidneys may allow these proteins to leak into the urine. It is a red flag for kidney damage.

“Studies done on kidneys and kidney health show that the more protein you have in your urine, the worse off your kidneys are going to be in the long run,” Tompson said. “Imagine protein as a spiked ball rolling through the kidney on the way to the bladder. The more protein we keep out of urine, the longer a kidney is likely to last.”

Learn more about proteinuria. 

Finding blood in urine can be alarming, but it’s not always indicative of chronic kidney disease on its own. Several conditions like infections or kidney stones can cause it.

Learn more about hematuria.

Regular check-ups and communication with your nephrologist or primary care provider can help you understand your lab results and adjust your treatment plan. Have questions? Contact NKF’s Patient Helpline NKF CARES for help.

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