kidney function test made simple
kidney function tests (also called renal function tests) check how well your kidneys are filtering waste from your blood. if you've seen terms like creatinine, BUN, or eGFR on your report, this guide will help you understand what they mean.
what do kidneys do?
your kidneys are two bean-shaped organs that filter about 200 liters of blood every day. their main jobs include:
- removing waste products and excess fluid
- balancing minerals like sodium, potassium, and calcium
- producing hormones that regulate blood pressure
- helping produce red blood cells
- keeping bones healthy
common kidney function markers
creatinine
a waste product from normal muscle activity. healthy kidneys filter it out of the blood. when kidney function decreases, creatinine levels typically rise.
blood urea nitrogen (BUN)
urea is a waste product from protein breakdown. BUN measures how much urea nitrogen is in your blood. it's affected by kidney function, diet, and hydration.
eGFR (estimated glomerular filtration rate)
this is calculated from your creatinine level, age, sex, and sometimes race. it estimates how much blood your kidneys filter per minute and is considered the best overall measure of kidney function.
BUN/creatinine ratio
the relationship between these two values can provide additional information about kidney health and hydration status.
why do doctors check kidney function?
- routine health screening
- monitoring conditions like diabetes or high blood pressure
- before starting certain medications
- investigating symptoms like swelling or changes in urination
- checking the effects of medications on kidneys
- monitoring existing kidney conditions
general reference ranges
creatinine
- males: approximately 0.7–1.3 mg/dL
- females: approximately 0.6–1.1 mg/dL
BUN
- typical range: 7–20 mg/dL
eGFR
- normal: 90 or above
- mildly decreased: 60–89
- moderately decreased: 30–59
- severely decreased: 15–29
- kidney failure: less than 15
note: ranges vary between labs. muscle mass affects creatinine levels, so athletes may have higher values without kidney problems.
what abnormal results may relate to
elevated creatinine or reduced eGFR may be associated with:
- dehydration (often temporary)
- high blood pressure over time
- diabetes
- certain medications
- urinary tract blockages
- kidney infections or diseases
a single abnormal result doesn't necessarily mean kidney disease. doctors typically look at trends over time and consider other factors.
questions doctors often ask
- how much water do you typically drink daily?
- have you noticed changes in your urination patterns?
- do you have diabetes or high blood pressure?
- what medications or supplements are you taking?
- have you had any recent illnesses or dehydration?
- is there family history of kidney disease?
- have you noticed any swelling in your legs or feet?
what information to prepare
- complete list of medications including over-the-counter drugs
- any supplements or herbal products you take
- your typical daily water intake
- any changes in urination (frequency, color, amount)
- previous kidney function test results
- history of diabetes, blood pressure, or kidney problems
frequently asked questions
can dehydration affect my results?
yes, dehydration can temporarily elevate creatinine and BUN levels. staying well-hydrated before your test gives more accurate results of actual kidney function.
do I need to fast for these tests?
usually not, but follow your doctor's instructions. some comprehensive panels may require fasting for other components being tested.
can kidney function improve?
it depends on the cause. if elevated values are due to dehydration or medication, they often return to normal. chronic conditions may require ongoing management. your doctor can advise based on your situation.
disclaimer: this article is for general educational purposes only. it is not medical advice and should not be used to diagnose or treat any condition. kidney function test results must be interpreted by a qualified healthcare provider who understands your complete medical history. always consult your doctor for personalized guidance.