Kidney Blood Tests: Which Labs Are Ordered and What They Mean
A complete guide to the blood and urine tests used to evaluate kidney health, detect chronic kidney disease, and monitor kidney function over time.
Last updated: April 10, 2026
To evaluate kidney function, doctors typically order creatinine, BUN, and eGFR as part of a comprehensive metabolic panel (CMP). These kidney blood tests measure how well the kidneys filter waste products from the blood and help identify kidney disease at its earliest stages.
What Is Kidney Disease?
Kidney disease occurs when the kidneys are damaged and cannot filter blood as effectively as they normally would. The kidneys are two bean-shaped organs located near the lower back. Their primary job is to filter waste products and excess fluid from the blood, producing urine. They also help regulate blood pressure, balance electrolytes like sodium and potassium, and support red blood cell production.
Chronic kidney disease (CKD) is the most common form, affecting roughly 1 in 7 American adults. CKD develops gradually over months or years, often without noticeable symptoms until significant damage has occurred. The two leading causes are diabetes and high blood pressure, which together account for about two-thirds of all CKD cases. Other causes include glomerulonephritis (inflammation of the kidney filters), polycystic kidney disease, and prolonged use of certain medications.
Acute kidney injury (AKI) is a sudden decline in kidney function that can develop within hours or days. Common triggers include severe dehydration, blood loss, infection (sepsis), urinary tract blockages, and certain medications. Unlike CKD, acute kidney injury may be reversible with prompt treatment. Blood tests are essential for detecting both acute and chronic kidney problems, often before symptoms appear.
Blood and Urine Tests for Kidney Function
The following table summarizes the key tests used to evaluate kidney health. Ranges may vary by laboratory and individual factors such as age, sex, muscle mass, and diet.
| Test | What It Measures | Normal Range | What Abnormal Means |
|---|---|---|---|
| Creatinine | Waste product from normal muscle activity | Men: 0.7–1.3 mg/dL Women: 0.6–1.1 mg/dL |
Elevated creatinine may indicate reduced kidney function; very high levels suggest serious kidney impairment |
| BUN (Blood Urea Nitrogen) | Waste product from protein breakdown | 7–20 mg/dL | High BUN may indicate kidney dysfunction, dehydration, or high protein intake; low BUN may suggest liver disease or malnutrition |
| eGFR (Estimated Glomerular Filtration Rate) | How well kidneys filter blood (calculated from creatinine) | >60 mL/min/1.73m² | 60–89 = mildly reduced; 15–59 = moderate CKD; <15 = kidney failure |
| BUN/Creatinine Ratio | Helps distinguish between kidney and non-kidney causes of elevated BUN | 10:1 to 20:1 | Ratio >20:1 may suggest dehydration, GI bleeding, or high protein intake; ratio <10:1 may suggest liver disease or malnutrition |
| Potassium | Electrolyte regulated by the kidneys | 3.5–5.0 mEq/L | High potassium (hyperkalemia) is common in advanced CKD and can affect heart rhythm |
| Sodium | Electrolyte involved in fluid balance | 136–145 mEq/L | Abnormal sodium levels may reflect the kidneys' reduced ability to regulate fluid and electrolyte balance |
| Calcium | Mineral regulated partly by the kidneys | 8.5–10.5 mg/dL | CKD can lead to low calcium levels due to impaired vitamin D activation, which may weaken bones |
| Urine Albumin (UACR) | Protein leaking into urine (early kidney damage marker) | <30 mg/g | 30–300 mg/g = moderately increased (microalbuminuria); >300 mg/g = severely increased (macroalbuminuria) |
Ranges may vary by lab, age, sex, and testing method. Always discuss results with a healthcare provider.
Stages of Chronic Kidney Disease by eGFR
Chronic kidney disease is classified into five stages based on eGFR. This staging system, established by the KDIGO (Kidney Disease: Improving Global Outcomes) guidelines, helps doctors determine how much kidney function remains and what treatment may be needed.
| Stage | eGFR (mL/min/1.73m²) | Kidney Function | What It Means |
|---|---|---|---|
| Stage 1 | ≥90 | Normal or high | Kidney damage present (e.g., protein in urine) but filtration is normal |
| Stage 2 | 60–89 | Mildly reduced | Mild loss of function with evidence of kidney damage; often no symptoms |
| Stage 3a | 45–59 | Mild to moderate | Noticeable decline; monitoring and lifestyle changes become important |
| Stage 3b | 30–44 | Moderate to severe | Complications such as anemia or bone disease may develop; closer monitoring needed |
| Stage 4 | 15–29 | Severely reduced | Significant impairment; preparation for dialysis or transplant may begin |
| Stage 5 | <15 | Kidney failure | Kidneys can no longer sustain life; dialysis or kidney transplant is typically necessary |
A single low eGFR result does not confirm CKD. The diagnosis requires reduced eGFR or other markers of kidney damage sustained for at least 3 months.
How These Tests Work Together
No single kidney test tells the complete story. Healthcare providers evaluate multiple markers together to determine whether the kidneys are functioning properly, how much damage may be present, and whether the condition is stable or worsening.
Creatinine and eGFR are the primary indicators of how well the kidneys filter waste. Creatinine is a waste product generated by normal muscle metabolism. When the kidneys are healthy, they efficiently remove creatinine from the blood. Rising creatinine levels — and falling eGFR — suggest that the kidneys are losing their filtering ability. However, creatinine alone can be misleading. A person with higher muscle mass may naturally have higher creatinine without kidney disease, which is why eGFR adjusts for factors like age and sex to provide a more accurate picture.
BUN adds another layer of information. While both BUN and creatinine rise when kidney function declines, BUN is also affected by protein intake, dehydration, gastrointestinal bleeding, and liver function. The BUN-to-creatinine ratio helps doctors distinguish between kidney-related and non-kidney causes. A ratio above 20:1, for example, may point toward dehydration or upper GI bleeding rather than intrinsic kidney disease.
Electrolyte monitoring is critical in kidney disease. The kidneys regulate potassium, sodium, and calcium balance. As kidney function declines, potassium may accumulate to dangerous levels (hyperkalemia), which can cause heart rhythm problems. Calcium levels may drop because damaged kidneys cannot activate vitamin D properly, leading to bone weakening over time.
The urine albumin-to-creatinine ratio (UACR) detects protein leaking into the urine — one of the earliest signs of kidney damage. Healthy kidneys keep protein in the blood, so finding albumin in urine indicates the kidney's filtering units (glomeruli) may be damaged. UACR is especially important for people with diabetes or high blood pressure, as it can reveal kidney damage years before eGFR starts to decline.
Acute Kidney Injury vs. Chronic Kidney Disease
The same blood tests are used for both conditions, but the pattern and timeline differ. Acute kidney injury (AKI) causes a rapid rise in creatinine over hours to days, often triggered by a specific event like severe dehydration, infection, surgery, or medication toxicity. In many cases, kidney function returns to normal with appropriate treatment.
Chronic kidney disease, by contrast, shows a gradual decline in eGFR over months or years. A single abnormal result does not confirm CKD — the KDIGO guidelines require evidence of kidney damage or reduced eGFR lasting at least three months to establish a diagnosis. This is why doctors often repeat kidney function tests before making conclusions. Tracking trends over time is more informative than any single lab result.
How Often Should Kidney Function Be Tested?
For most healthy adults, kidney function is checked during routine annual blood work as part of a comprehensive metabolic panel. People at higher risk may need more frequent testing.
- Diabetes or high blood pressure: At least once a year, including both blood tests (creatinine/eGFR) and urine albumin
- Known CKD stage 1–2: Every 6–12 months, depending on the rate of decline and underlying cause
- CKD stage 3: Every 3–6 months, with electrolyte monitoring
- CKD stage 4–5: Every 1–3 months, with close monitoring of potassium, calcium, phosphorus, and anemia markers
- Family history of kidney disease or polycystic kidney disease: Annual screening starting at an age determined by the healthcare provider
People taking medications that may affect kidney function — such as NSAIDs, certain blood pressure medications (ACE inhibitors or ARBs), or contrast dye for imaging studies — may also need periodic kidney function checks.
Frequently Asked Questions
What blood tests check kidney function?
The most common kidney blood tests are creatinine, BUN (blood urea nitrogen), and eGFR (estimated glomerular filtration rate). These are typically part of a comprehensive metabolic panel. Doctors may also check electrolytes like sodium, potassium, and calcium, along with urine albumin to detect early damage to the kidney filters.
What is eGFR and what does it mean?
eGFR stands for estimated glomerular filtration rate. It is calculated from creatinine levels along with age, sex, and body size to estimate how efficiently the kidneys filter waste. An eGFR above 60 is generally considered normal. An eGFR below 60 sustained for three or more months may indicate chronic kidney disease, and an eGFR below 15 suggests kidney failure.
Can kidney disease be detected early with blood tests?
Yes. Blood tests like creatinine and eGFR, combined with a urine albumin test, can detect kidney damage in early stages — often before any symptoms develop. This is why routine screening is recommended for people with diabetes, high blood pressure, or a family history of kidney disease. Early detection allows for interventions that may slow or prevent further damage.
How often should kidney function be tested?
For healthy adults, kidney function is typically checked once a year during routine blood work. People with diabetes or high blood pressure may need annual or more frequent testing. Those with known CKD are usually tested every 3 to 6 months, and advanced CKD (stages 4–5) may require monthly monitoring.
What is the difference between BUN and creatinine?
Both are waste products filtered by the kidneys, but they come from different sources. BUN is produced when the liver breaks down protein, while creatinine comes from normal muscle metabolism. Creatinine is generally a more reliable kidney function marker because BUN levels are influenced by protein intake, hydration status, and liver function. Doctors often look at both together, including the BUN-to-creatinine ratio, for a fuller picture.
Can dehydration affect kidney blood test results?
Yes, dehydration can temporarily raise both BUN and creatinine levels, making kidney function appear worse than it actually is. BUN is particularly sensitive to hydration status and often rises more sharply than creatinine with dehydration. If dehydration is suspected, a healthcare provider may recommend retesting after adequate fluid intake to see whether levels return to normal.
What are the stages of chronic kidney disease?
CKD is classified into five stages based on eGFR. Stage 1 (eGFR 90+) and stage 2 (eGFR 60–89) have kidney damage with relatively preserved function. Stage 3 is divided into 3a (eGFR 45–59) and 3b (eGFR 30–44), representing moderate decline. Stage 4 (eGFR 15–29) is severe. Stage 5 (eGFR below 15) is kidney failure, which typically requires dialysis or a kidney transplant.
Sources
- KDIGO. Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International Supplements. 2024.
- National Kidney Foundation (NKF). About Chronic Kidney Disease.
- Mayo Clinic. Chronic Kidney Disease — Diagnosis and Treatment.
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Kidney Disease Tests.
- MedlinePlus. Kidney Function Tests. U.S. National Library of Medicine.
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Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges vary by laboratory and individual factors. Always discuss results with a qualified healthcare provider.