Kidney Function: Which Blood Tests Are Commonly Used?

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Kidney function blood tests are used to estimate how well your kidneys filter waste, keep electrolytes in balance, and support normal fluid and acid-base control. The blood tests most people see on lab reports are creatinine with estimated glomerular filtration rate (eGFR), blood urea nitrogen (BUN), and electrolytes. These markers may appear as individual tests or inside a basic metabolic panel (BMP), comprehensive metabolic panel (CMP), renal function panel, or kidney profile.

Kidney testing can feel confusing because “kidney function” is not one single number. Creatinine and eGFR mainly speak to filtration. BUN reflects urea nitrogen handling but is influenced by diet, hydration, liver function, gastrointestinal bleeding, and other factors. Electrolytes help show whether kidney or hormonal problems are affecting potassium, sodium, bicarbonate, and fluid balance. Cystatin C can provide another estimate of kidney filtration, especially when creatinine may be misleading. And even though this article focuses on blood tests, urine testing is often essential because early kidney damage may show up as albumin in urine before filtration drops.

Common kidney function blood tests

Most routine kidney assessment starts with a chemistry blood test. According to the National Institute of Diabetes and Digestive and Kidney Diseases, clinicians commonly use a blood test for GFR and a urine test for albumin to check for chronic kidney disease; creatinine is the waste product used to estimate GFR in many reports. NIDDK explains CKD testing with eGFR and urine albumin.

Test or panel	What it measures	Why it is used	Important limitations
Serum creatinine	Creatinine, a waste product from muscle metabolism, in blood	Used to estimate GFR and monitor kidney filtration trends	Affected by muscle mass, diet, hydration, some medications, and acute illness
eGFR	A calculated estimate of filtration rate, usually from creatinine and demographic variables	Helps classify kidney filtration level and monitor changes over time	An estimate, not a direct measurement; less reliable in some body-size, muscle-mass, pregnancy, and acute kidney injury situations
BUN	Urea nitrogen, a waste product from protein metabolism	Adds context for waste handling, dehydration, high protein breakdown, and kidney function	Less specific for kidney disease than eGFR; can rise or fall for non-kidney reasons
Electrolytes	Sodium, potassium, chloride, and carbon dioxide/bicarbonate	Shows fluid and acid-base balance; potassium and bicarbonate are especially important in kidney disease	Abnormal results may come from medications, dehydration, endocrine disorders, vomiting/diarrhea, or lab handling issues
Cystatin C	A protein made by cells and filtered by the kidneys	Alternative or additional marker for estimating GFR when creatinine may be less reliable	May be affected by inflammation, thyroid disease, steroid use, smoking, and other factors; often costs more than creatinine
BMP or CMP	Blood chemistry panel including creatinine, BUN, glucose, calcium, and electrolytes; CMP also includes liver-related markers and proteins	Common screening or monitoring panel that includes kidney-related markers	Broad panel, not kidney-specific; abnormal values need clinical interpretation
Renal function panel	Typically includes creatinine, BUN, electrolytes, calcium, phosphorus, albumin, and related chemistry values	Often used for kidney disease monitoring, medication monitoring, and electrolyte/mineral balance	Panel contents can vary by lab or order set

MedlinePlus describes a comprehensive metabolic panel as a routine blood test that includes BUN and creatinine, along with electrolytes and other chemistry measurements used to evaluate kidney health, liver health, blood glucose, proteins, and fluid balance. MedlinePlus: comprehensive metabolic panel.

Creatinine and eGFR: the core kidney function blood test

Serum creatinine is often the first number people notice on a kidney-related lab report. Creatinine is generated from normal muscle metabolism and removed from the blood by the kidneys. When filtration decreases, creatinine often rises. But creatinine by itself is hard to interpret because two people can have the same creatinine value and different kidney filtration depending on age, sex, muscle mass, body size, and other factors.

That is why most labs report eGFR alongside creatinine. eGFR stands for estimated glomerular filtration rate. It is an estimate of how much blood the kidney filters per minute, adjusted to a standard body surface area. The National Kidney Foundation explains that the standard way to estimate GFR is a blood test measuring creatinine, and that cystatin C may also be used in some estimates. National Kidney Foundation: eGFR.

eGFR result	General interpretation	What usually matters next
90 or higher	Often considered normal filtration if there are no other signs of kidney damage	Urine albumin, urinalysis, blood pressure, diabetes status, and trend over time
60–89	Mildly decreased filtration; may be normal for some people, especially with aging, if no kidney damage markers exist	Whether uACR is abnormal, whether result is persistent, and whether risk factors are present
45–59	Mild to moderate decrease	Repeat testing, urine albumin, medication review, blood pressure and diabetes management, and clinical context
30–44	Moderate to severe decrease	Closer monitoring and evaluation for complications such as anemia, mineral/bone issues, acidosis, and medication dose adjustments
15–29	Severe decrease	Nephrology involvement is commonly considered; planning depends on symptoms, complications, and progression
Below 15	Very low kidney function; may be described as kidney failure in the right clinical context	Urgent individualized care planning; dialysis or transplant evaluation may be discussed depending on the situation

NIDDK notes that a GFR of 60 or more is generally in the normal range, a GFR below 60 may indicate kidney disease, and a GFR of 15 or less is called kidney failure in many clinical discussions. Those cutoffs are useful, but they are not the whole interpretation. Kidney disease is generally defined by reduced kidney function or evidence of kidney damage that persists for more than three months. A one-time low eGFR during dehydration, infection, medication change, or acute illness may need repeat testing rather than immediate labeling as chronic kidney disease. NIDDK: evaluating CKD.

Modern U.S. laboratory practice has also moved away from race-based eGFR reporting. The National Kidney Foundation describes implementation of CKD-EPI 2021 equations that do not include a race coefficient, and NIDDK lists race-free equations for adults. NKF: race-free eGFR implementation and NIDDK: eGFR equations for adults.

BUN, electrolytes, and kidney panels

BUN stands for blood urea nitrogen. Urea is produced when the body breaks down protein, and the kidneys help remove it. A high BUN can occur when kidney filtration is reduced, but it can also rise with dehydration, high protein intake, gastrointestinal bleeding, fever, severe stress, corticosteroids, or increased tissue breakdown. A low BUN may occur with low protein intake, overhydration, pregnancy, or certain liver conditions. Because it is influenced by many non-kidney factors, BUN is usually interpreted with creatinine, eGFR, electrolytes, symptoms, and the clinical situation. MedlinePlus: BUN blood test.

The BUN-to-creatinine ratio may appear on some reports. Clinicians may use it as one clue when evaluating dehydration, reduced blood flow to the kidneys, or other causes of abnormal kidney chemistry. However, the ratio is not a stand-alone diagnosis. It can be skewed if either BUN or creatinine is abnormal for non-kidney reasons.

Electrolytes matter because the kidneys help regulate potassium, sodium, chloride, and bicarbonate. Potassium is especially important because both high and low potassium can affect heart rhythm and muscle function. Bicarbonate or carbon dioxide on a metabolic panel helps evaluate acid-base balance; chronic kidney disease can contribute to metabolic acidosis when the kidneys cannot clear acid normally. Sodium and chloride help show fluid and salt balance, but they are influenced by hydration, diuretics, heart failure, vomiting, diarrhea, and hormone-related conditions.

Basic metabolic panels and comprehensive metabolic panels are common ways kidney-related markers are ordered. A BMP typically includes glucose, calcium, sodium, potassium, chloride, carbon dioxide/bicarbonate, BUN, and creatinine. A CMP includes those kidney-related chemistry tests plus liver enzymes, bilirubin, albumin, and total protein. A renal function panel is more kidney-focused and often includes phosphorus and albumin in addition to creatinine, BUN, and electrolytes. The exact panel contents can vary, so it is worth reading the component list rather than assuming every “kidney panel” is identical.

Cystatin C and when a second filtration marker helps

Cystatin C is a blood protein produced by many cells in the body and filtered by the kidneys. It can be used to estimate GFR by itself or in combination with creatinine. MedlinePlus notes that cystatin C is not affected by muscle size in the same way as creatinine, and that creatinine and cystatin C may be used together to calculate eGFR in certain adult cases. MedlinePlus: GFR test.

A clinician may consider cystatin C when creatinine-based eGFR does not fit the clinical picture. Examples include unusually high or low muscle mass, frailty, limb amputation, some eating patterns, body-building supplement use, or situations where a medication dose depends on a more accurate kidney estimate. Cystatin C is not perfect. It may be influenced by inflammation, thyroid disease, smoking, corticosteroid use, obesity, and other factors. Still, the combined creatinine-cystatin C equation can improve decision-making for some people, especially when eGFR is near a threshold that affects medication dosing, imaging contrast decisions, referral decisions, or CKD staging.

Some people also encounter creatinine clearance, a test that compares creatinine in blood with creatinine collected in urine over a timed period, often 24 hours. It is less convenient than a simple blood draw and is prone to collection errors, but it may be useful in selected situations. MedlinePlus notes that creatinine clearance may help when blood creatinine is hard to interpret, such as very high or very low muscle mass. MedlinePlus: creatinine test.

Why urine tests are often ordered with kidney function blood tests

Blood tests estimate filtration and chemistry balance, but they can miss early kidney damage. The most important companion test is often the urine albumin-to-creatinine ratio, also called uACR or UACR. Albumin is a blood protein. Healthy kidney filters usually keep albumin in the blood, while damaged filters can allow albumin to leak into urine. NIDDK describes UACR as a urine test that compares albumin with urine creatinine and gives categories such as 30 mg/g or less as normal and more than 30 mg/g as potentially concerning for kidney disease. NIDDK: urine albumin testing.

Urine testing is especially important for people with diabetes, high blood pressure, cardiovascular disease, a family history of kidney failure, prior kidney problems, or medications that can affect the kidneys. A urinalysis may also look for blood, protein, glucose, ketones, white blood cells, casts, and other findings. MedlinePlus describes urinalysis as a urine test commonly used to check for urinary tract infections, kidney problems, diabetes, and other conditions. MedlinePlus: urinalysis.

If the blood test shows…	A urine test can help answer…
Normal eGFR	Is there albumin leakage or blood that suggests kidney damage despite preserved filtration?
Low eGFR	Is albumin present, and how much kidney damage risk does it suggest?
High creatinine after exercise or dehydration	Are there persistent urine abnormalities, or does the result appear temporary?
Abnormal potassium or bicarbonate	Are there urine findings that support kidney involvement or another cause?

How to prepare for kidney function blood tests

Preparation depends on the exact test or panel. Many kidney function blood tests do not require fasting, but a CMP may be ordered fasting because it includes glucose and other chemistry values. If your order includes fasting instructions, follow those instructions unless your clinician tells you otherwise. Continue prescribed medications unless the ordering clinician specifically advises holding a medication.

Several everyday factors can affect kidney-related results:

• Hydration status: Dehydration can concentrate blood chemistry values and may raise BUN, creatinine, or the BUN-to-creatinine ratio.
• Recent intense exercise: Heavy exercise can temporarily increase creatinine or muscle-related markers.
• Diet and supplements: A large cooked-meat meal, creatine supplements, high-protein intake, or unusual diet changes may affect creatinine or BUN.
• Medications: Diuretics, ACE inhibitors, ARBs, NSAIDs such as ibuprofen or naproxen, some antibiotics, lithium, certain antivirals, chemotherapy drugs, and contrast-related exposures can affect kidney results or require monitoring.
• Acute illness: Vomiting, diarrhea, fever, infection, low blood pressure, or hospitalization can produce temporary kidney changes.
• Lab handling: Potassium can be falsely high if blood cells break during collection or processing; repeat testing may be needed when a result does not match the clinical picture.

For trend monitoring, consistency helps. If possible, use the same lab system, test under similar conditions, and compare results over time rather than focusing only on one value. Small changes may reflect normal biological and laboratory variation; large or persistent changes deserve clinical review.

Cost and access considerations

The cost of kidney function blood tests depends on how they are ordered, where the sample is collected, insurance status, and whether a clinician visit or ordering service is required. A creatinine test with eGFR is often relatively inexpensive compared with specialized tests, while cystatin C and broader panels may cost more. If testing is ordered through a clinician for a medical reason, insurance may cover some or all of the lab cost, subject to deductibles, copays, network rules, and medical-necessity requirements.

If you are comparing cash-pay or self-ordered testing, compare the effective total cost, not just the advertised test price. Check whether the quoted amount includes the lab draw, required clinician or physician-order fee, result review, taxes, and any follow-up requirements. Also check whether the test is available in your state, whether you must visit a specific collection network, and whether the panel includes the markers you actually need. A “kidney panel” may include creatinine and eGFR but not urine albumin; another package may include both blood and urine markers. The federal Clinical Laboratory Fee Schedule is a Medicare payment reference, not a guaranteed consumer cash price, but it illustrates that official laboratory payment rates and consumer prices are not the same thing. CMS: Clinical Laboratory Fee Schedule.

What to do if kidney function results are abnormal

An abnormal kidney blood test should be interpreted with context, not in isolation. Practical next steps may include:

1. Compare with prior results. A stable eGFR of 58 over several years is different from a drop from 95 to 58 in a month.
2. Ask whether repeat testing is needed. Repeat testing can help distinguish persistent kidney impairment from dehydration, medication effects, acute illness, or lab variation.
3. Check urine albumin and urinalysis if not already done. eGFR and uACR together give a more complete view of kidney risk than either alone.
4. Review medications and supplements. Ask specifically about NSAIDs, diuretics, blood pressure medicines, diabetes medicines, lithium, antibiotics, contrast exposure, and supplements such as creatine.
5. Address major risk factors. Blood pressure control, diabetes management, smoking cessation, cardiovascular risk reduction, and avoiding kidney-toxic exposures are common pillars of kidney protection.
6. Know when to seek urgent care. Severe weakness, chest pain, fainting, confusion, shortness of breath, very low urine output, severe swelling, or a very high potassium result can be urgent.

Guidelines from KDIGO emphasize evaluating chronic kidney disease using both GFR category and albuminuria category, with cause and duration also considered. KDIGO: CKD evaluation and management. For consumers, the key takeaway is simple: kidney blood tests are powerful screening and monitoring tools, but the best interpretation comes from the pattern across blood tests, urine tests, risk factors, and time.

 

FAQs

What blood tests are used to check kidney function?

The most common kidney function blood tests are serum creatinine with eGFR, BUN, electrolytes, and sometimes cystatin C. These may be ordered alone or as part of a BMP, CMP, renal function panel, or kidney profile.

Is eGFR a blood test or a calculation?

eGFR is usually a calculation based on a blood marker, most often creatinine. Some eGFR calculations use cystatin C, and some use both creatinine and cystatin C. The blood test measures the marker; the lab report calculates the estimate.

Which is better: creatinine or cystatin C?

Neither is universally “better” for everyone. Creatinine is common, inexpensive, and well established, but it is affected by muscle mass and diet. Cystatin C can be helpful when creatinine may be misleading, but it has its own limitations and may cost more. In selected cases, using both markers gives a better estimate.

Can kidney disease be present with normal creatinine?

Yes. A creatinine value within the lab reference range does not always rule out kidney disease. eGFR may reveal reduced filtration, and urine albumin testing may detect kidney damage even when filtration is still preserved.

What is the difference between a CMP and a renal function panel?

A CMP is a broad chemistry panel that includes kidney markers, liver markers, proteins, glucose, calcium, and electrolytes. A renal function panel is more kidney-focused and often includes phosphorus and albumin. Exact components vary by lab and order set.

Do kidney function blood tests require fasting?

Many kidney-related blood tests do not require fasting. However, a CMP or other panel may be ordered fasting because it includes glucose or because the ordering clinician wants standardized conditions. Follow the instructions on your lab order.

How often should kidney function be checked?

Frequency depends on risk. People with diabetes, high blood pressure, known kidney disease, cardiovascular disease, certain medications, or prior abnormal results may need periodic monitoring. People without risk factors may only have kidney markers checked during routine care or when symptoms or medications make testing relevant.

What symptoms suggest I should ask about kidney testing?

Many early kidney problems cause no symptoms. Possible warning signs include swelling in the legs or around the eyes, foamy urine, blood in urine, high blood pressure, fatigue, shortness of breath, nausea, itching, changes in urination, or unexplained electrolyte abnormalities. Symptoms can have many causes, so lab testing is only one part of evaluation.

Sources

• National Institute of Diabetes and Digestive and Kidney Diseases: Chronic Kidney Disease Tests & Diagnosis
• National Kidney Foundation: Estimated Glomerular Filtration Rate (eGFR)
• MedlinePlus: Comprehensive Metabolic Panel
• MedlinePlus: BUN Blood Test
• MedlinePlus: Glomerular Filtration Rate Test
• KDIGO: CKD Evaluation and Management Guideline