Kidney Function Panel — Your Complete Guide

What Is a Kidney Function Panel?

Your kidneys are two bean-shaped organs, each about the size of your fist, located on either side of your spine just below your rib cage. Every single day, they filter roughly 50 gallons of blood, removing waste products, excess fluid, and toxins that leave your body as urine. They also regulate your blood pressure, balance your electrolytes, help produce red blood cells, and keep your bones healthy by activating vitamin D.

A kidney function panel is a set of blood (and sometimes urine) tests that evaluate how well your kidneys are performing these vital jobs. Because kidneys can lose a significant amount of their function before you notice any symptoms, these tests are essential for catching problems early — when they are most treatable.

Chronic kidney disease (CKD) affects an estimated 37 million Americans, and most do not know they have it. That is why kidney function testing is a routine part of medical care, especially for people with diabetes, high blood pressure, or a family history of kidney disease.

What Does This Test Include?

A kidney function panel typically includes several markers, some measured directly and some calculated.

Creatinine — A waste product generated by normal muscle metabolism. Your kidneys filter creatinine out of the blood and into the urine at a very steady rate, making it an excellent marker of kidney function. Normal serum creatinine is roughly 0.7 to 1.3 mg/dL for men and 0.6 to 1.1 mg/dL for women. Higher creatinine suggests the kidneys are not filtering as efficiently as they should.

Estimated Glomerular Filtration Rate (eGFR) — This is calculated from your creatinine level, age, sex, and sometimes race. It estimates how many milliliters of blood your kidneys filter per minute. A normal eGFR is 90 mL/min or above. An eGFR between 60 and 89 may warrant monitoring. Below 60 for three months or more is the definition of chronic kidney disease. Below 15 indicates kidney failure.

Blood Urea Nitrogen (BUN) — Urea is a waste product created when your body breaks down protein. The kidneys filter it out. Normal BUN is about 7 to 20 mg/dL. BUN is a useful but less specific marker than creatinine — it can be elevated by dehydration, a high-protein diet, gastrointestinal bleeding, or certain medications even when the kidneys are fine.

BUN-to-Creatinine Ratio — This ratio helps distinguish between different causes of elevated BUN. A ratio above 20:1 often suggests a pre-renal cause like dehydration, while a ratio that is more proportional points to actual kidney damage.

Cystatin C — A newer and increasingly used marker. Cystatin C is a protein produced at a constant rate by all cells in the body and filtered by the kidneys. Unlike creatinine, it is not affected by muscle mass, making it more accurate in certain populations — including elderly patients, very muscular individuals, and those with low muscle mass. Normal is approximately 0.6 to 1.0 mg/L.

Electrolytes (Sodium, Potassium, Chloride, Bicarbonate) — The kidneys are master regulators of electrolytes. Abnormal electrolyte levels can indicate impaired kidney function. Potassium is especially important because high potassium (hyperkalemia) can develop in kidney disease and is dangerous for the heart.

Calcium and Phosphorus — The kidneys help regulate these minerals. In kidney disease, phosphorus often rises and calcium may fall, which can lead to bone problems over time.

Urine Albumin (Microalbumin) — This is a urine test, not a blood test, but it is a critical part of kidney evaluation. Healthy kidneys keep albumin (a large protein) in the blood. When the kidneys are damaged, albumin leaks into the urine. A urine albumin-to-creatinine ratio (UACR) below 30 mg/g is normal. Between 30 and 300 mg/g is moderately increased (formerly called microalbuminuria) and above 300 mg/g is severely increased. This test can detect kidney damage years before eGFR starts to drop.

When Is This Test Ordered?

Kidney function tests are ordered in several common scenarios.

During routine health checkups, especially if you have risk factors. Diabetes is the number one cause of kidney disease, and high blood pressure is number two. If you have either condition, your doctor should check your kidney function and urine albumin at least once a year.

If you have symptoms that might suggest kidney problems, such as changes in urination (more or less than usual, foamy or dark urine), swelling in your ankles, feet, or face, persistent fatigue, nausea, loss of appetite, muscle cramps, or itchy skin.

When you are taking medications that can affect the kidneys, including NSAIDs (like ibuprofen and naproxen), certain blood pressure medications (ACE inhibitors and ARBs, which are actually protective but need monitoring), some antibiotics, and contrast dye used in CT scans.

To monitor existing kidney disease and see whether it is stable, improving, or worsening. The stage of CKD is determined by your eGFR and urine albumin levels, and tracking these over time guides treatment decisions.

How to Prepare

A basic kidney function blood test usually requires no fasting. However, if your doctor is also ordering tests that require fasting (like a glucose or lipid panel), you may need to fast for 10 to 12 hours.

If a urine test is included, you may be asked to provide a first-morning urine sample (the most concentrated sample of the day) or a random spot urine sample collected at the lab. In some cases, your doctor may ask for a 24-hour urine collection, where you save all your urine over a full day in a special container. This is less common now that spot urine ratios have become the standard.

Stay well hydrated before your test, as dehydration can temporarily raise creatinine and BUN levels and make your results look worse than they really are. Tell your doctor about all medications and supplements you take.

Understanding Your Results

The most important number on your kidney panel is your eGFR. Here is how doctors classify kidney function based on eGFR:

• Stage 1 (eGFR 90 or above): Normal kidney function, but other signs of kidney damage may be present (like protein in the urine)
• Stage 2 (eGFR 60–89): Mildly reduced function. Often discovered incidentally. May just need monitoring.
• Stage 3a (eGFR 45–59): Mildly to moderately reduced. Worth paying closer attention and managing risk factors aggressively.
• Stage 3b (eGFR 30–44): Moderately to severely reduced. Regular nephrology follow-up may be recommended.
• Stage 4 (eGFR 15–29): Severely reduced. Planning for possible dialysis or transplant begins.
• Stage 5 (eGFR below 15): Kidney failure. Dialysis or transplant is typically needed.

A single low eGFR does not automatically mean you have chronic kidney disease. The diagnosis requires that the reduction persist for at least three months. Acute illness, dehydration, or recent intense exercise can temporarily lower eGFR.

Urine albumin is the other pillar of kidney assessment. Even if your eGFR is normal, persistently elevated urine albumin is an early warning sign of kidney damage.

What Abnormal Results Might Mean

Elevated creatinine and low eGFR — The kidneys are not filtering waste as well as expected. Causes range from dehydration and medication side effects (temporary and fixable) to diabetes, hypertension, glomerulonephritis, polycystic kidney disease, or other chronic conditions.

Elevated BUN with normal creatinine — Often caused by dehydration, a high-protein diet, gastrointestinal bleeding, or heart failure — not necessarily a kidney problem.

Elevated potassium — Can develop as kidney function declines because the kidneys cannot excrete potassium efficiently. High potassium (above 5.5 mEq/L) can cause dangerous heart rhythm problems and needs prompt attention.

Protein in the urine (albuminuria) — An early marker of kidney damage, especially in diabetes. It can also be caused by high blood pressure, infections, heavy exercise, fever, or heart failure.

Low bicarbonate — The kidneys help regulate acid-base balance. As kidney function worsens, bicarbonate may fall, leading to metabolic acidosis.

What to Do Next

If your kidney function tests are normal, keep up the good work. Stay hydrated, manage your blood pressure and blood sugar if applicable, use NSAIDs sparingly, and continue with regular checkups.

If results are mildly abnormal, your doctor will likely recommend repeat testing in a few weeks to months to see if the abnormality persists. They may also order a kidney ultrasound to look at the size and structure of your kidneys.

For confirmed chronic kidney disease, the focus shifts to slowing progression. This involves tight blood pressure control (usually with an ACE inhibitor or ARB), blood sugar management in diabetes, dietary adjustments (lower sodium, and in later stages, lower potassium and phosphorus), weight management, smoking cessation, and avoiding nephrotoxic medications.

Your doctor may refer you to a nephrologist (kidney specialist) if your eGFR is below 30, if it is declining rapidly, if there is significant protein in your urine, or if the cause is unclear.

Upload Your Results to LabGPT

Kidney function results involve several interconnected markers, and it can be hard to know what the big picture looks like from numbers alone. Upload your kidney panel to LabGPT for a friendly, easy-to-understand breakdown of each value. We will help you see where things stand and prepare meaningful questions for your healthcare provider.

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This content is for educational purposes only and is not medical advice. Always consult your healthcare provider about your lab results.