Your kidneys work around the clock — filtering your blood, removing waste, regulating blood pressure, and balancing electrolytes. They do all of this silently, which is exactly the problem. Kidney disease often has no symptoms until significant damage has already occurred.

A kidney function blood test is one of the most important preventive health checks you can get, especially if you have risk factors like high blood pressure, diabetes, or a family history of kidney disease.

A kidney function panel — sometimes called a renal function panel — measures several markers that reflect how well your kidneys are filtering waste from your blood.

The key markers include:

Creatinine — a waste product produced by normal muscle metabolism. Healthy kidneys filter creatinine out of the blood efficiently. When kidneys are damaged or stressed, creatinine builds up.

eGFR (Estimated Glomerular Filtration Rate) — calculated from your creatinine level, age, sex, and race, eGFR estimates how many milliliters of blood your kidneys filter per minute. It's the most direct measure of kidney function available through a blood test.

BUN (Blood Urea Nitrogen) — urea is a waste product from protein metabolism. Like creatinine, elevated BUN can indicate reduced kidney filtration, though it can also be affected by diet and hydration.

BUN/Creatinine Ratio — the ratio of these two markers helps distinguish between kidney disease and other causes of elevated BUN, such as dehydration or high protein intake.

Electrolytes — sodium, potassium, chloride, and bicarbonate levels reflect the kidneys' ability to maintain fluid and acid-base balance.

eGFR is expressed as a number representing milliliters filtered per minute per 1.73 m² of body surface area. Here's how to interpret it:

A single low eGFR reading doesn't necessarily mean kidney disease — dehydration, intense exercise, or certain medications can temporarily affect results. Persistent low eGFR over multiple tests is more significant.

Normal creatinine ranges vary by sex and muscle mass:

• Men: 0.74–1.35 mg/dL
• Women: 0.59–1.04 mg/dL

Higher muscle mass produces more creatinine, so athletes and people with more muscle may have slightly higher creatinine levels that are still normal for them.

People with diabetes — High blood sugar damages the small blood vessels in the kidneys over time. Diabetic kidney disease (diabetic nephropathy) is the leading cause of kidney failure in the United States.

People with high blood pressure — Hypertension is the second leading cause of kidney failure. The kidneys and blood pressure are closely linked — damaged kidneys raise blood pressure, and high blood pressure damages kidneys.

People taking certain medications — NSAIDs (ibuprofen, naproxen), certain antibiotics, and some blood pressure medications can affect kidney function with long-term use.

People with a family history of kidney disease — Polycystic kidney disease and other inherited conditions run in families.

Adults over 60 — Kidney function naturally declines with age. Baseline testing helps track changes over time.

People who are overweight or obese — Excess weight increases the risk of both diabetes and high blood pressure, the two leading causes of kidney disease.

Anyone with recurring kidney stones — Stones can damage kidney tissue and indicate metabolic issues worth monitoring.

The challenge with kidney disease is that it's often called a "silent" condition. By the time symptoms appear, significant damage may have already occurred. When symptoms do develop, they can include:

• Swelling in the legs, ankles, or feet (edema)
• Fatigue and weakness
• Changes in urination frequency or color
• Foamy or bubbly urine (a sign of protein in the urine)
• Persistent itching
• Nausea or loss of appetite
• Difficulty concentrating
• Muscle cramps, especially at night
• Shortness of breath

If you're experiencing any of these symptoms, a kidney function panel is an important first step.

You may have heard of the Comprehensive Metabolic Panel (CMP). This is a broader blood test that includes kidney function markers (creatinine, BUN, eGFR) alongside liver function markers, glucose, and electrolytes — all in one draw.

If you want a comprehensive snapshot of your metabolic health, the CMP is an efficient option. If you're specifically focused on kidney health, a standalone renal panel gives you the same kidney markers with more detail.

Hydration matters. Dehydration can temporarily raise creatinine and BUN levels, making results look worse than they are. Drink normal amounts of water in the days before your test — don't overhydrate, but don't restrict fluids either.

Avoid intense exercise the day before. Strenuous exercise temporarily raises creatinine levels as muscles break down.

Fasting may be required. Some kidney panels include glucose or other fasting markers. Check your specific test requirements when you order.

List your medications. Certain drugs affect kidney markers. Knowing what you take helps interpret your results accurately.

You don't need a referral or insurance to check your kidney function. Reliable Exams offers direct-access lab testing — you order online, visit a nearby Quest Diagnostics or LabCorp location, and receive your results privately within 1–3 business days.

This is especially valuable for people who want to monitor their kidney health proactively, track the effects of a new medication, or simply get a baseline before any problems develop.

A single abnormal result doesn't mean you have kidney disease. Your next steps depend on how far outside the normal range your results fall:

Mildly elevated creatinine or reduced eGFR: Retest in a few weeks after ensuring you were well-hydrated and hadn't exercised intensely beforehand. Many mild abnormalities resolve on their own.

Consistently abnormal results: Follow up with a healthcare provider for further evaluation, including a urine test to check for protein (proteinuria), which is an early sign of kidney damage.

Significantly abnormal results: Seek medical attention promptly. Early intervention can slow or stop the progression of kidney disease.

The best time to check your kidney function is before you have any symptoms. Catching reduced kidney function early — when it's at stage 1 or 2 — gives you the best chance of slowing progression through lifestyle changes, medication adjustments, and closer monitoring.

Don't wait for symptoms that may never come until it's too late. A kidney function panel is a simple, affordable way to know where you stand.