The 2026 Levels Guide to kidney blood tests

These biomarkers can help you detect dysfunction—and take action—before it has a chance to impair your metabolic health.

WRITTEN BY

Stephanie Eckelkamp, MS, RDN, LDN

Updated: 02/12/2026|10 min read

Your kidneys may be the unsung heroes of metabolic health. These two fist-sized organs, situated just below the rib cage on either side of your spine, play a role in everything from waste clearance and electrolyte balance to hormone production and blood pressure regulation.

The problem: Declining kidney function initially has no obvious symptoms. However, blood tests provide a window into kidney health. A comprehensive metabolic panel (CMP)---which most healthcare providers order as routine lab work at your annual physical---includes many markers of kidney function. If any results come back out of range, your provider may order additional blood and urine testing, depending on your specific symptoms and risk factors. 

This guide explores essential tests for kidney health, what each marker says about renal and metabolic function, and steps to take if any results fall outside the healthy range. 

Interpreting kidney test results requires medical expertise. Though this guide provides educational information, always discuss your specific results with healthcare providers who can develop personalized recommendations.

Why kidney function tests matter for health

The kidneys influence nearly every system in the body, so routinely assessing their function is key. While they're most well known for their role in filtering waste from the blood and eliminating it via the urine, they do all of the following and more:

• Clear waste from the blood, such as urea (a byproduct of protein metabolism), creatinine (a byproduct of muscle turnover or breakdown), and acids like uric acid.
• Maintain an appropriate balance of fluids and electrolytes (like sodium, potassium, calcium, phosphorus, and magnesium) in the body, which influences blood pressure, heart and muscle contractions, bone health, acid-base balance, and more.
• Help regulate blood sugar levels by either excreting excess blood glucose or assisting in endogenous glucose production (gluconeogenesis) when necessary.
• Produce erythropoietin, a hormone required for red blood cell production.
• Convert inactive vitamin D (calcidiol) to its biologically active form (calcitriol) so the body can use it.

Because these organs play so many roles, declining kidney function can contribute to cardiovascular disease, fluid retention, dysregulated blood sugar, bone loss, anemia, gout, vitamin D deficiency, metabolic acidosis, and other issues. Unfortunately, kidney disease is "silent"---it lacks symptoms until it's advanced and the kidneys are badly damaged. 

In fact, more than one in seven American adults (35 million people) have kidney disease, yet 90 percent don't know it. Many common health problems that plague Americans can contribute to kidney damage. High blood pressure and diabetes, in particular, can damage the delicate blood vessels within the kidneys' filtering units (called nephrons), impairing their ability to filter the blood and regulate fluid and electrolyte balance.

Fortunately, early detection through routine testing helps to prevent further damage.

When should you consider kidney function tests?

Everyone should have basic kidney function labs done yearly as a part of a routine CMP. This panel, and additional blood or urine tests, may be done more frequently based on your current health status, symptoms, and risk factors. Testing may be particularly important in these situations:

• You have metabolic risk factors: Hypertension, diabetes, metabolic syndrome, and obesity can strain and damage the kidneys.
• You have cardiovascular disease: Heart failure, in particular, reduces blood flow to the kidneys, which can cause damage and impair their function.
• You have a family history of kidney disease: Chronic kidney disease (CKD) can be a result of both environmental and genetic factors, while other forms of kidney disease, like polycystic kidney disease (PKD), are considered inherited diseases.
• You regularly take medication: Some drugs are known to damage the kidneys when taken repeatedly or in large amounts, and others are cleared by the kidneys and have the potential to build up in the body during later stages of kidney disease. Monitoring kidney labs helps inform which meds need to be adjusted or switched.
• You have urinary symptoms: These may include blood in your urine, foamy urine, pain or burning during urination, frequent urges to urinate, or urinating less than usual.
• You have other unexplained symptoms: These may include fatigue, trouble concentrating, swollen ankles or feet, persistent eye puffiness, poor appetite, muscle cramping, dry and itchy skin, a metallic taste in the mouth, and nausea and vomiting.

What do blood test markers tell you about kidney health?

Kidney function tests measure things like:

• The rate at which the kidneys filter the blood
• The buildup of various waste products in the blood
• The acidity of the blood
• Electrolytes levels in the blood
• The amount of protein in the urine

Having one of these markers outside the standard range does not necessarily mean you have impaired kidney function. A variety of factors can influence each marker. That said, among the markers below, an eGFR below the standard range, coupled with protein in your urine, may be the biggest red flag.

While medical providers may test different markers depending on the specific patient, the tests below tend to be the most common. Note that eGFR, creatinine, blood urea nitrogen (BUN), sodium, potassium, and anion gap are part of a CMP.

Core kidney function markers

Estimated glomerular filtration rate (eGFR)

eGFR estimates how well your kidneys are filtering or clearing waste from the blood. It's a calculated estimate of how much blood passes through the glomerulus (the bundle of tiny blood vessels located in each kidney's nephrons). This number is typically calculated based on your age, sex, and blood levels of creatinine (a waste product generated from muscle metabolism; levels can be influenced by muscle mass and recent meat intake). An eGFR may be calculated with cystatin C when creatinine levels are altered by non-kidney-related factors.

Considered the best overall measure of kidney function, eGFR is used to help determine the stage of kidney disease and monitor kidney function over time. Significantly lower eGFR levels have also been noted in individuals with metabolic syndrome, making it an indirect marker of overall metabolic health.

Interpreting your eGFR levels: For eGFR, a higher number is better.

• Standard range (>90 mL/min/1.73m²): Keep in mind that "normal" varies by age---it naturally decreases as you get older. For adults ages 60 to 69 without kidney disease, average eGFR is 85; for adults older than 70 without kidney disease, average eGFR is 75.
• Mildly reduced (60 to 89): If you're in this range and have signs of kidney damage, such as protein in the urine (measured by a uACR test), you may have early kidney disease (CKD stage 1 or 2). People in this range should closely monitor their eGFR and may want to avoid or reduce intake of certain medications that stress the kidneys, such as ibuprofen.
• Low (<60): Results this low suggest kidney damage. If your levels are in this range for more than three months, you may have moderate to severe kidney disease. 
• Very low (<15): Extremely low eGFR indicates kidney failure. To stay alive, you'll need dialysis to adequately filter the blood or a kidney transplant.

Creatinine

Normal muscle breakdown generates most of the body's creatinine, a waste product in the blood. Because the body produces it at a relatively constant rate and only the kidneys clear it, elevated blood creatinine may indicate reduced creatinine clearance due to kidney function.

Interpreting your creatinine levels: Creatinine is most valuable when used to calculate eGFR; looking at this marker alone doesn't give you a full picture of kidney health. Still, it's good to know the appropriate range and what may impact your creatinine levels.

• Standard range (0.6 to 1.2 mg/dL for men and 0.5 to 1.1 mg/dL for women): Creatinine levels tend to be lower in women because they typically have less muscle mass compared to men. Important to note: Kidney function may be decreased by as much as 50 percent before there's a noticeable rise in creatinine, so being in this range doesn't guarantee good kidney function.
• Elevated (>1.2 mg/dL for men and >1.1 mg/dL for women): This may be related to kidney disease or an acute kidney injury---or it may not indicate kidney problems at all. High creatinine levels are also seen with dehydration, recent intense exercise, muscle injuries, greater muscle mass (as in bodybuilders), creatine supplements, eating a large amount of meat, and certain drugs like antibiotics, acid blockers, and cholesterol medications.
• Low (<0.6 mg/dL for men and <0.5 mg/dL for women): While it's less common to have low creatinine, it may be caused by muscle loss due to age or an illness, malnutrition, serious liver disease, or pregnancy.

For people whose creatinine levels may be influenced by non-kidney-related factors (such as extremes in muscle mass), your healthcare provider has the option to order a cystatin C test, which can also be used to calculate eGFR.

Cystatin C

Cystatin C is a protein produced at a relatively constant rate by all cells with a nucleus in the body and filtered exclusively by the kidneys. It's used to calculate eGFR only when your healthcare provider determines that creatinine may be an unreliable marker of kidney function. Cystatin C is less influenced by muscle mass and diet than creatinine, and can be useful when creatinine is unreliable---though levels can still be affected by factors like inflammation, thyroid disease, smoking, steroids, and obesity. For that reason, it is a potentially more accurate marker of kidney function than creatinine in populations like the elderly, bodybuilders, people taking creatine supplements, or those on high-protein diets. It may also be more reliable in early stages of kidney disease when creatinine may be low.

Interpreting your cystatin C levels: Like creatinine, cystatin C levels are most valuable when used to calculate eGFR. By itself, it does not give you a full picture of kidney health. 

• Standard range (0.51 to 0.98 mg/L): This is considered normal for adults.
• Elevated (>0.99 mg/L): This range tends to correlate with a decline in kidney function, regardless of age, muscle mass, diet, or supplements. Elevations are also associated with cardiovascular disease in people with and without kidney disease. However, cystatin C levels may be elevated due to non-kidney-related factors such as thyroid disease, smoking, steroid medications, obesity, and inflammation, therefore limiting its use in these instances.
• Low (<0.51 mg/L): Low cystatin C levels are not common, and their relationship with health and kidney function is less clear.

Urine albumin-to-creatinine ratio (uACR)

Urine albumin-to-creatinine ratio (uACR) compares the amount of albumin (a protein) with creatinine (a waste product) in urine. Normally, albumin stays in the blood, and healthy kidneys prevent it from leaking into urine. But damaged nephrons allow more albumin to pass through. Creatinine, on the other hand, is a normal waste product present in urine. Measuring this ratio helps detect abnormal levels of protein in the urine (proteinuria), which is an indicator of early stage kidney damage. Along with eGFR (an indicator of kidney function), it can be used to diagnose CKD.

While the uACR is not part of a routine lab panel, it's often performed to help identify kidney problems as early as possible in people with the symptoms and risk factors outlined above.

Interpreting your uACR levels: Looking at your uACR levels along with your eGFR can provide a fuller picture of overall kidney health. The higher your levels, the more protein in your urine, which may indicate a greater level of kidney damage.

• Standard range (<30 mg/g): This range indicates no---or very little---protein in the urine. But you can still be diagnosed with CKD if your eGFR is less than 60 for more than three months.
• Elevated (>30 to 300 mg/g): Elevated uACR may suggest moderate kidney damage; levels greater than 300 mg/g may suggest greater damage and more advanced kidney disease. When levels are greater than 30 mg/g for more than three months, you may be diagnosed with CKD, even if your eGFR is still greater than 60. However, temporary elevations in urinary albumin may be triggered by dehydration, intense exercise, infections, or fever, and these aren't associated with long-term damage.

Blood urea nitrogen (BUN)

The blood urea nitrogen (BUN) test measures levels of urea nitrogen, a waste product that your body generates when it breaks down dietary proteins. The liver produces urea nitrogen, which then travels through the blood and is eventually filtered by the kidneys and excreted with urine. While some urea nitrogen in the blood is normal, too much could indicate sub-optimal filtering by the kidneys. If you have severe kidney disease (kidney failure), urea nitrogen can build up in the blood to dangerously high levels, contributing to symptoms and complications like nausea, fatigue, itching, muscle cramps, cognitive dysfunction, and even coma or stroke.

BUN is considered a less accurate indicator of kidney health than creatinine, as hydration, protein intake, and other factors may impact levels. However, it may be elevated earlier in kidney disease, making it helpful to monitor if you have known risk factors. 

Interpreting your BUN levels: To assess kidney health, BUN should always be evaluated alongside other markers such as creatinine and eGFR. Abnormalities in BUN alone do not suggest kidney problems.

• Standard range (7 to 20 mg/dL): Although this range is normal for adults, it doesn't necessarily mean your kidneys are functioning optimally.
• Elevated (>20 mg/dL): This may indicate decreased kidney function, particularly if you also have an elevated creatinine and decreased eGFR. However, BUN could also be elevated for non-kidney reasons, such as dehydration, fever or infections, high-protein diets, high stress, GI bleeding, severe burns, or certain medications like tetracycline antibiotics or steroids. 
• Low (<7 mg/dL):These may occur with serious liver disease, overhydration, malnutrition/starvation, or normally in pregnancy.

Blood urea nitrogen-to-creatinine ratio (BUN/Cr)

BUN/Cr is a calculated ratio comparing BUN to creatinine levels. This test is typically used to identify the cause of impaired kidney function. Specifically, it helps determine if the issue is:

• Pre-renal (>20:1): Caused by decreased blood flow to the kidneys, such as from heart failure or dehydration.
• Intrinsic renal (10:1 to 20:1): Caused by direct damage within the kidney tissues, such as damage to the glomeruli or tubules.
• Post-renal (<10:1): Caused by an issue beyond the kidneys, such as a blockage in the urinary tract caused by a kidney stone or tumor, which causes back pressure on the kidneys.

Other factors that may cause an elevated BUN/Cr ratio include GI bleeding, high-protein diet, or steroid medications; while a low BUN/Cr ratio may be due to serious liver disease, malnutrition, or rhabdomyolysis (rapid muscle breakdown).

Electrolyte and acid-base balance markers

Sodium

Sodium is an essential electrolyte mineral that helps maintain proper fluid balance, particularly in the blood vessels and the fluid around cells. This influences blood pressure and regulates nerve function and muscle contraction and relaxation throughout the body (including the heart) and helps usher nutrients into cells and waste products out of cells.

Normally, kidneys excrete or reabsorb sodium as needed to keep levels in a healthy range. Impaired kidney function could lead to abnormal sodium levels in the blood (particularly low levels, which may trigger muscle twitching or eventually seizures)---but typically, this would not occur until more advanced stages of kidney disease 

Interpreting your sodium levels: Other markers are better at initially identifying kidney problems, but monitoring sodium levels can be particularly important for people with existing kidney disease to prevent things like worsening hypertension and fluid overload.

• Standard range (135 to 145 mEq/L): Keep in mind, sodium levels are tightly regulated by the body, and values may not be altered with early kidney disease.
• Elevated (hypernatremia; >145 mEq/L): Sodium 146 to 149 mEq/L) is mildly elevated, 150 to 159 mEq/L) is moderately elevated, and higher than 160 mEq/L) is severely elevated. Elevations are typically related to dehydration, which could be caused by not drinking enough water, diarrhea, vomiting, frequent urination (caused by diabetes or diuretic medication), and kidney dysfunction. High salt intake usually doesn't raise serum sodium in otherwise healthy people (it more often increases thirst and fluid retention), but it can still worsen blood pressure.
• Low (hyponatremia; <135 mEq/L): Sodium less than [130 to 134 mEq/L](https://www.uptodate.com/contents/overview-of-the-treatment-of-hyponatremia-in-adults#:~:text=Moderate%20to%20severe%20hyponatremia%20(serum,Fluid%20restriction) is considered mild hyponatremia, [120 to 129 mEq/L](https://www.uptodate.com/contents/overview-of-the-treatment-of-hyponatremia-in-adults#:~:text=Moderate%20to%20severe%20hyponatremia%20(serum,Fluid%20restriction) is moderate hyponatremia, and [less than 120 mEq/L](https://www.uptodate.com/contents/overview-of-the-treatment-of-hyponatremia-in-adults#:~:text=Moderate%20to%20severe%20hyponatremia%20(serum,Fluid%20restriction) is severe hyponatremia. These low levels may be related to an acute kidney injury, advanced stages of kidney disease, or kidney failure, as damaged kidneys may have difficulty removing extra fluid, which can dilute the blood. Low sodium could also be caused by vomiting, diarrhea, hypothyroidism, or medications that cause your body to retain water such as SSRI antidepressants and some seizure medications. 

Potassium

Another electrolyte mineral required for proper nerve and muscle function, potassium helps your heartbeat stay regular. Along with sodium, it helps regulate fluid balance in the body, specifically within the cells, and it helps transport nutrients into cells and waste products out.

As with sodium, the kidneys tightly regulate potassium levels, adjusting excretion to match intake. Poor kidney function can lead to dangerous potassium elevations that require immediate attention, as they can significantly impact cardiac function. But high potassium levels are often not seen until more advanced stages of kidney disease.

Interpreting your potassium levels: Other markers are better at initially identifying kidney problems, but monitoring potassium levels can be particularly important for people with existing kidney disease to prevent cardiac complications.

• Standard range (3.5 to 5.0 mEq/L): As with sodium, potassium is tightly regulated by the body and values may not be altered with early kidney disease.
• Elevated (hyperkalemia; >5 or 5.5 mEq/L): Levels above 6.0 to 7.0 mEq/L are considered severe and may lead to dangerous heart arrhythmias, muscle weakness, and paralysis. The most common cause is kidney disease. Other causes include: severe hyperglycemia, as high blood sugar can cause shifts in potassium from the inside of cells into the bloodstream, and medications that impair potassium excretion, like certain blood pressure drugs. High dietary intake of potassium rarely causes hyperkalemia in people with normal kidney function.
• Low (hypokalemia <3.5 mEq/L): Potassium less than 3 to 3.5 mEq/L is considered mild hypokalemia, 2.5 to 2.9 mEq/L is moderate hypokalemia, and below 2.5 mEq/L is severe hypokalemia. Impaired kidney function could lead to hypokalemia, but it more often causes hyperkalemia. Other causes include the use of prescription diuretics or excess laxatives, fluid loss from nausea or vomiting, adrenal disorders, and alcohol use disorder.

Anion gap

An anion gap blood test helps measure the acidity of your blood. It's used to identify acid-based disorders, including metabolic acidosis, which can occur most commonly as a complication of chronic kidney disease and uncontrolled diabetes due to a lack of insulin. It's determined by measuring the difference in positively charged electrolytes (sodium, potassium) and negatively charged electrolytes (chloride, bicarbonate) in your blood. Normally, healthy kidneys remove excess acid from the blood, but advanced kidney disease impairs this process.

Interpreting your anion gap level: Like the electrolyte markers above, your anion gap isn't an early indicator of kidney dysfunction, but monitoring your levels can help prevent complications in more advanced stages of kidney disease. Other factors can also influence your anion gap.

• Standard range (8 to 12 mEq/L): Normal levels can be seen in cases of early kidney disease. (Reference ranges vary by lab/assay.)
• Elevated (>12 mEq/L): Levels in this range coupled with low levels of bicarbonate (another electrolyte) can suggest high anion gap metabolic acidosis. This can be caused by.-,High%2Danion%2Dgap%20metabolic%20acidosis,-An%20increase%20in) kidney failure, diabetic ketoacidosis, lactic acidosis, or excessive amounts of a salicylate medication like aspirin.
• Low (<8 mEq/L): This is less common, but may be a result of low levels of albumin in the blood, which could be triggered by heart disease, liver disease, certain cancers, and kidney disease.

What's next if your kidney test results are out of range?

Always consult with your doctor about out-of-range test results. They will look at your full clinical picture and make appropriate recommendations.

They typically start by ruling out temporary influences such as dehydration, high-protein meals, certain medications and supplements, and recent intense exercise. If you need to stay on any medication long-term, your doctor may advise adjusting your dosage to help preserve kidney function.

Often, you need repeat testing to help confirm or rule out kidney issues. For example, eGFR should be measured at least twice over three months to diagnose chronic kidney disease. Your doctor may also refer you to a nephrologist (kidney specialist) for more comprehensive evaluation if kidney disease is suspected or if the cause of abnormal labs is unclear.

Further diagnostic testing may include:

• A 24-hour urine collection test
• Genetic testing for inherited kidney diseases such as autosomal dominant polycystic kidney disease (ADPKD) or Alport syndrome
• Imaging studies, such as a kidney ultrasound
• Blood sugar and blood pressure (the two main drivers of chronic kidney disease)

If you are diagnosed with kidney disease, or if you have another metabolic condition that puts you at risk (such as diabetes, high blood pressure, obesity, or heart disease) you can take steps to help prevent or slow the progression of kidney problems. Recommendations often include:

• Prioritizing exercise and adequate hydration
• Keeping blood sugar and blood pressure in a healthy range with a healthy diet and regular exercise
• Losing weight if you are overweight
• Quitting smoking
• Switching some of animal proteins to plant-based options, which appear to be less taxing on the kidneys
• Adjusting your dietary intake of sodium, protein, potassium, and phosphorus intake if you have more advanced kidney disease

Conclusion

The kidneys are key regulators of our internal environment, maintaining fluid and electrolyte balance, regulating blood pressure, and clearing metabolic waste. When kidney function becomes compromised, it often signals or contributes to broader metabolic dysfunction---and once kidney damage occurs, these organs have a limited ability to repair themselves. 

Common lab tests, many of which are part of the comprehensive metabolic panel (CMP) ordered at your annual physical, can help detect kidney function abnormalities while you have time to take action and preserve function via diet and lifestyle changes.

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