Kidney Function Tests: Creatinine, BUN, eGFR, and Uric Acid

Quick answer

Doctors check kidney health with four main blood tests: creatinine, eGFR, BUN, and uric acid. eGFR, short for estimated filtration rate, is the single most useful number. A falling eGFR across two or more tests is worth a closer look, even if each result still falls in the normal range.

Creatinine

What it measures: a waste product from your muscles. Your kidneys filter it out of your blood at a steady rate.

The lab's normal range: 0.7 to 1.3 mg/dL for men; 0.6 to 1.1 mg/dL for women.

Why it matters: a rising creatinine level means your kidneys are filtering less well. The same reading of 1.2 mg/dL can mean different things for different people. In a 25 year old man it is probably normal. In a 70 year old woman it could point to serious kidney trouble, since muscle mass differs from person to person.

Important: creatinine alone does not tell the full story. Your doctor also needs to factor in your age and sex. That is exactly what the eGFR test does.

eGFR (estimated glomerular filtration rate)

What it measures: a calculated estimate of how well your kidneys filter blood, based on your creatinine, age, and sex.

The lab's normal range: above 90 mL/min/1.73m squared. The healthy target range: above 90.

Stages of kidney disease by eGFR:

• 90 and above: normal, or stage 1 kidney disease if kidney damage is also present.
• 60 to 89: a mild drop, or stage 2 kidney disease if damage is present.
• 45 to 59: stage 3a kidney disease.
• 30 to 44: stage 3b kidney disease.
• 15 to 29: stage 4 kidney disease.
• Below 15: stage 5, also called kidney failure.

The trend matters more than any single result. A drop of more than 5 mL/min in one year is worth investigating, even if both readings still count as normal.

A score that sits just above the cutoff is not the same as a strong one. Here is what a healthy eGFR and creatinine result actually looks like, not just what counts as normal.

BUN (blood urea nitrogen)

What it measures: a nitrogen waste product left over from breaking down protein.

The lab's normal range: 7 to 20 mg/dL.

Why it goes up or down:

• High BUN: can come from dehydration, a high-protein diet, gut bleeding, or kidney trouble.
• Low BUN: can come from liver disease, poor nutrition, a low-protein diet, or drinking too much water.

The BUN-to-creatinine ratio helps your doctor tell dehydration apart from a real kidney problem. High BUN with normal creatinine often points to dehydration. High BUN that rises along with creatinine points to a kidney issue.

Uric acid

What it measures: a byproduct left over when your body breaks down purines, a substance found in certain foods.

The lab's normal range: 3.4 to 7.0 mg/dL for men; 2.4 to 6.0 mg/dL for women. The healthy target range: below 6 mg/dL.

Why it matters for Filipinos:

• Gout, a painful joint condition caused by high uric acid, is common.
• Diets rich in red meat, organ meats, seafood, beer, and sweet drinks raise uric acid.
• Uric acid that stays high raises your risk for heart and kidney disease on its own.
• It often shows up together with metabolic syndrome and high triglycerides.

What to do if your level runs high:

• Cut back on alcohol, especially beer, and on sugary drinks.
• Eat less organ meat, certain seafood, and red meat.
• Drink more water.
• Keep a healthy weight.
• Ask your doctor about medicine like allopurinol or febuxostat if you have gout or a very high level.

Urine albumin-to-creatinine ratio (ACR)

What it measures: tiny amounts of a protein called albumin leaking into your urine. This is often the earliest sign of kidney damage in people with diabetes or high blood pressure.

The lab's normal range: below 30 mg/g.

Why it matters: this can show up before eGFR starts to drop, especially if you have diabetes or high blood pressure. This test checks urine, not blood, but it is still part of a full kidney check.

Cystatin C (an advanced test)

What it measures: a kidney filtration marker that is more sensitive than creatinine.

Why it matters: muscle mass affects it less than creatinine does, so it helps when creatinine-based eGFR gives a confusing picture, such as in very muscular people, older adults, or people who have lost a lot of muscle.

Availability: not part of most standard panels, but many labs offer it as an add-on.

Common patterns

Pattern 1: Early kidney decline

• Creatinine slowly rising over several tests.
• eGFR under 90, trending down over the years, for example from 95 to 88 to 82.
• Often paired with high blood pressure or diabetes.
• What to do: get tighter control of blood pressure and blood sugar, review any medicines that stress the kidneys, and consider a urine ACR test.

Pattern 2: High uric acid

• Uric acid above 7 mg/dL in men or above 6 mg/dL in women.
• Often paired with metabolic syndrome.
• What to do: change your diet, lose weight, drink more water, and use medicine if gout is confirmed.

Pattern 3: Dehydration that looks like kidney trouble

• High BUN.
• Normal or only slightly high creatinine.
• A BUN-to-creatinine ratio above 20 to 1.
• What to do: drink more water, then retest.

Pattern 4: Early diabetic kidney disease

• eGFR still normal.
• Urine ACR above 30 mg/g.
• Diabetes already diagnosed, or blood sugar in the pre-diabetes range.
• What to do: get aggressive control of blood sugar and blood pressure, and ask about a kidney specialist referral.

Why kidney disease is often caught late

Three reasons this happens:

1. No symptoms until late. Your kidneys have a lot of spare capacity. Symptoms like fatigue, swelling, foamy urine, or less urine usually only show up at stage 3b or later.
2. Normal ranges can hide a trend. A drop from an eGFR of 120 to 95 is a 21 percent loss of function, yet both numbers still count as normal.
3. Standard panels often skip the urine ACR test. Without it, the earliest sign of kidney damage linked to diabetes or blood pressure gets missed.

What raises kidney risk

• Diabetes. The leading cause of kidney disease worldwide, and cases are rising fast.
• High blood pressure. Often not well controlled.
• Genetics. Some groups carry a higher genetic risk for certain kidney conditions.
• Herbal and traditional remedies. Some contain substances that can harm the kidneys.
• Overusing pain relievers called NSAIDs. Regular use damages the kidneys over time.
• High uric acid. Often driven by diet.

How to protect your kidneys

The habits with the strongest evidence behind them:

• Keep blood pressure tight. Aim for under 130/80 mmHg.
• Keep blood sugar tight if you have diabetes. Aim for an HbA1c under 7 percent, or whatever your doctor recommends.
• Stay well hydrated. Enough water helps your kidneys filter well.
• Limit NSAID pain relievers. Regular use adds up to real damage over time.
• Be careful with herbal products. Some can harm your kidneys.
• Keep a healthy weight. Extra weight puts direct strain on kidney filtering.
• Cut back on salt. This helps control blood pressure.
• Treat sleep apnea if you have it. It is linked to faster kidney decline on its own.
• Get eGFR and urine ACR checked regularly. Every 6 to 12 months if you are at higher risk.

Want your kidney markers checked as part of a full panel? A &you Labs panel includes creatinine, eGFR, BUN, and uric acid as standard.

Frequently asked questions

What counts as a good eGFR?

Above 90 is the healthy target range. Above 60 is generally fine for adults without diabetes or high blood pressure. Below 60 for 3 months or more meets the definition of chronic kidney disease.

Why does my creatinine rise after exercise?

Hard exercise within 24 hours of a blood draw can push creatinine up for a short time, because it breaks down some muscle tissue. Skip intense workouts the day before testing for the most accurate reading.

Are kidney tests reliable for very muscular people?

Creatinine-based eGFR can make kidney function look worse than it really is in very muscular people, since more muscle means more creatinine, apart from filtering. Cystatin C is a more accurate marker in this case.

Can kidney function come back after it drops?

A sudden kidney injury from medicine, dehydration, or illness often heals fully. Chronic kidney disease usually does not reverse, but proper care can slow it down a lot.

How often should I check my kidney function?

Once a year for healthy adults. Every 6 months if you have diabetes, high blood pressure, or a past abnormal result. Every 3 months when starting a medicine that can affect the kidneys.

Key takeaways

• eGFR is the single most useful kidney number. The trend across tests matters more than any one result.
• Creatinine alone is not enough. It needs to be read alongside your age and sex, which is what eGFR does.
• Uric acid matters a lot for Filipinos, given how common gout and metabolic syndrome are.
• A urine ACR test can catch kidney damage linked to diabetes or blood pressure before eGFR even starts to drop.
• Kidney disease is often caught late, so yearly checks are worth the effort.