Kidney Function Tests: Normal Ranges & What Results Mean Test: Normal Range, High/Low Meaning | WellAlly

What Are Kidney Function Tests?

Your kidneys are remarkable filtration plants. Every day, they filter about 200 quarts of blood, removing waste and excess fluid to produce urine. They also regulate electrolytes, blood pressure, and produce hormones.

Kidney function tests (also called renal function tests or KFTs) evaluate how well your kidneys are working. These tests can detect kidney disease early, often before symptoms appear.

What kidney function tests typically include:

BUN (Blood Urea Nitrogen): Waste product from protein breakdown

Creatinine : Waste product from muscle metabolism

eGFR (estimated Glomerular Filtration Rate): How well kidneys filter waste

Electrolytes : Sodium, potassium, chloride, bicarbonate

Albumin (sometimes): Protein that can leak into urine with kidney damage

Why These Tests Matter

Kidney disease is often called a "silent killer" because you can lose up to 90% of kidney function before feeling sick. Early detection through kidney function tests allows treatment that can slow or prevent progression to kidney failure.

Understanding Your Results

BUN (Blood Urea Nitrogen)

What it measures : Waste product from protein breakdown, filtered by kidneys

Normal range : 7-20 mg/dL

What it means : Elevated BUN suggests reduced kidney filtration or other causes.

Causes of Abnormal BUN

Factor

Effect

What to Do

Dehydration

Increases

Most common cause of elevated BUN with normal creatinine. Rehydration normalizes BUN.

Kidney dysfunction

Increases

Reduced filtration elevates both BUN and creatinine. Further evaluation needed to determine cause and severity.

GI bleeding

Increases

Blood in digestive tract is broken down to protein, elevating BUN significantly. BUN rises disproportionately to creatinine.

Low protein intake or malnutrition

Decreases

Reduced protein breakdown lowers BUN. Not concerning unless associated with malnutrition.

Always tell your doctor about medications, supplements, and recent health events before testing.

Creatinine

What it measures : Waste product from muscle metabolism, filtered by kidneys

Normal range : 0.7-1.3 mg/dL (varies by muscle mass)

What it means : Creatinine is more specific for kidney function than BUN. Elevated creatinine indicates reduced kidney filtration.

Important notes:

Muscle mass affects creatinine: more muscle = higher baseline creatinine

Very muscular people may have creatinine at upper limit of normal with healthy kidneys

Elderly or frail people may have low creatinine despite kidney dysfunction

eGFR (estimated Glomerular Filtration Rate)

What it measures : How well kidneys filter waste (calculated from creatinine, age, gender)

Normal range : ≥90 mL/min/1.73m²

What it means : eGFR is the best single measure of kidney function. It estimates how much blood passes through kidney filters (glomeruli) each minute.

Understanding Your Results ( mL/min/1.73m² )

Normal kidney function—healthy filtration

Mild kidney damage—monitor and treat underlying cause

Stage 3a CKD—treatment to slow progression

Stage 3b CKD—active treatment to prevent progression

Stage 4 CKD—prepare for kidney failure treatment

Stage 5 CKD—dialysis or transplant evaluation needed

Chronic Kidney Disease (CKD) Stages

CKD is staged based on eGFR. Stage 1 (eGFR ≥90 with kidney damage) through Stage 5 (eGFR ＜15, kidney failure). Early stages (1-3) often have no symptoms. Treatment focuses on slowing progression and treating complications. Once eGFR falls below 30, preparation for renal replacement therapy (dialysis/transplant) begins.

BUN:Creatinine Ratio

Comparing BUN to creatinine provides important information:

Normal ratio : 10:1 to 20:1

Elevated ratio (＞20:1) :

Dehydration : Kidneys concentrate urea more than creatinine

GI bleeding : Blood protein breakdown elevates BUN

High protein intake : Increases urea production

Corticosteroid use : Increases protein breakdown

Normal or low ratio (10:1 to 20:1) :

Kidney dysfunction : BUN and creatinine rise proportionally

Reduced muscle mass : Creatinine lower than expected

Electrolytes

Kidney dysfunction affects electrolyte balance:

Sodium : Usually normal until advanced kidney disease

Potassium : Can be elevated when eGFR ＜30 (kidneys can't excrete potassium)

Potassium above 5.0 mEq/L with kidney dysfunction requires attention

Potassium above 6.0 mEq/L is dangerous (heart rhythm risk)

Bicarbonate : Decreases as kidney disease progresses (metabolic acidosis)

Low bicarbonate in kidney disease reflects impaired acid excretion

Treatment with oral bicarbonate may be needed

When Are Kidney Function Tests Ordered?

When Your Doctor Might Order Kidney Function Tests

Kidney function testing is common in many situations.

You're having routine health screening

Kidney function is routinely screened, especially for adults over 40 or with risk factors (diabetes, hypertension, family history). Early detection allows treatment to slow progression.

You have diabetes

Diabetes is the leading cause of kidney disease. Annual kidney function testing (creatinine, eGFR, urine albumin) is recommended for all diabetic patients.

You have high blood pressure

Hypertension is both a cause and consequence of kidney disease. Regular testing monitors kidney health and guides blood pressure treatment goals.

You're taking medications affecting kidneys

NSAIDs, certain antibiotics, contrast dye, and other medications can affect kidney function. Baseline and periodic monitoring detect medication effects.

You have swelling in legs, ankles, or around eyes

Edema (fluid retention) can indicate kidney dysfunction. Kidney function tests assess whether kidneys are properly filtering and excreting fluid.

You have changes in urination

Urinating more or less than usual, foamy urine (protein), or blood in urine warrant kidney function evaluation.

You have unexplained fatigue or weakness

Advanced kidney disease can cause anemia and fatigue. Kidney function testing assesses whether reduced kidney function is contributing.

Your Action Plan Based on Results

If eGFR ≥90 and other tests normal:

Continue healthy lifestyle

Stay hydrated

Limit NSAID use (ibuprofen, naproxen)

Control blood pressure and blood sugar

Repeat testing as recommended (every 1-3 years if healthy)

If eGFR 60-89 (mildly decreased):

Confirm with repeat testing in 1-3 months

Identify and treat underlying cause

Optimize blood pressure control (target ＜130/80)

Control blood sugar if diabetic

Avoid nephrotoxins (NSAIDs, contrast dye)

Monitor for protein in urine (albumin-to-creatinine ratio)

If eGFR 30-59 (moderate CKD):

Comprehensive evaluation to identify cause

Refer to nephrologist (kidney specialist)

Aggressive risk factor modification: Blood pressure ＜130/80 A1C ＜7% if diabetic SGLT2 inhibitors if diabetic (kidney protective) ACE inhibitors or ARBs (kidney protective) Avoid NSAIDs completely

Blood pressure ＜130/80

A1C ＜7% if diabetic

SGLT2 inhibitors if diabetic (kidney protective)

ACE inhibitors or ARBs (kidney protective)

Avoid NSAIDs completely

Monitor for complications: anemia, bone disease, acidosis, potassium elevation

Repeat eGFR every 3 months

If eGFR 15-29 (severe CKD):

Nephrologist care essential

Prepare for renal replacement therapy

Monitor closely for complications

Dietary modifications may be needed

Access planning for future dialysis if indicated

If eGFR ＜15 (kidney failure):

Nephrologist care mandatory

Dialysis or transplant evaluation

Urgent symptoms may require emergency dialysis

When Kidney Dysfunction Requires Urgent Evaluation

Sudden rise in creatinine (acute kidney injury)

Potassium above 6.0 mEq/L (dangerous heart rhythm risk)

Severe symptoms: confusion, seizures, pericarditis, fluid overload (lungs)

Anuria (no urine output for >6 hours) or oliguria (very little urine)

Rapidly progressive kidney failure

Known kidney disease with sudden worsening

⚠️ These findings require urgent medical evaluation. Contact your doctor or seek emergency care. Acute kidney injury can be reversible with prompt treatment but can be life-threatening if untreated.

Protecting Your Kidneys

Whether your kidney function is normal or impaired, these steps help protect your kidneys:

Stay hydrated : Drink water throughout the day. Dehydration stresses kidneys.

Control blood pressure : High blood pressure damages kidneys over time. Target ＜130/80.

Control blood sugar : Diabetes is the leading cause of kidney disease. Tight glucose control protects kidneys.

Limit NSAIDs : Ibuprofen, naproxen, and similar medications reduce blood flow to kidneys. Use cautiously or avoid if kidney dysfunction exists.

Limit salt : High sodium increases blood pressure and kidney stress. Target ＜2,300 mg daily.

Maintain healthy weight : Obesity increases kidney disease risk. Weight loss of 5-10% improves kidney health.

Don't smoke : Smoking accelerates kidney disease progression.

Limit alcohol : Heavy alcohol use dehydrates and stresses kidneys.

Exercise regularly : Physical activity lowers blood pressure and improves kidney health.

Get vaccinated : Infections can cause acute kidney injury. Stay up to date on flu, pneumonia, and other vaccines.

Common Questions

Can I improve my kidney function?

Do I need to fast for kidney function tests?

Can drinking water improve my kidney function?

Are NSAIDs bad for kidneys?

What are the early symptoms of kidney disease?

What foods are bad for kidneys?

Disclaimer : This information is for educational purposes only and does not constitute medical advice. Always consult your healthcare provider to interpret your kidney function test results and determine appropriate management.

Track Your Kidney Function Panel Results

Monitor your levels over time, identify trends, and share your history with your doctor.