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A kidney function report can contain several unfamiliar numbers. Two you are likely to see are creatinine and eGFR. They are closely connected, but they describe different things: creatinine is a waste product measured in your blood, while eGFR estimates how well your kidneys filter blood.
Your doctor considers these results alongside your urine tests, medical history and previous reports. Understanding them can help you follow changes in your kidney health without drawing conclusions from one number alone.
What is creatinine?
Creatinine is a waste product produced through normal muscle activity. Your kidneys filter it from the blood and remove it through urine. If the kidneys are filtering less effectively, the amount of creatinine in the blood may rise.
However, creatinine also depends on factors such as muscle mass, diet and recent physical activity. Someone with more muscle may naturally have a higher result than someone with less muscle. This is one reason your doctor looks beyond whether a number falls inside the laboratory’s reference range.
What does eGFR tell you?
The letters eGFR stand for estimated glomerular filtration rate. Laboratories commonly calculate it using your blood creatinine result, age and sex. It estimates how quickly the kidneys filter blood and helps doctors assess kidney function more meaningfully than creatinine alone.
The word “estimated” matters. The result is useful, but it is not an exact measurement, and unusual muscle mass or certain illnesses can make it less reliable. In some situations, your doctor may request another blood marker called cystatin C and use both results to improve the estimate.
How should you understand the number?
In adults, an eGFR of 90 or above generally falls within the normal filtration range. However, kidney damage can still be present if other tests show a problem, such as persistent albumin in the urine. An eGFR between 60 and 89 does not, by itself, establish chronic kidney disease when there is no other evidence of kidney damage.
An eGFR below 60 that remains low for at least three months meets a criterion for chronic kidney disease. A single low result needs assessment, but it cannot tell your doctor whether the change is recent or long-standing. Previous reports, repeat testing and other findings help establish that distinction.
Why is a urine test important too?
The kidneys normally keep most albumin, a protein in the blood, from passing into urine. An increased amount can be a sign of kidney damage, including when the eGFR is still relatively well preserved.
The urine albumin-to-creatinine ratio, usually written as uACR or ACR, measures this leakage. Your doctor uses eGFR and uACR together to understand kidney health, assess risk and guide follow-up. A blood test alone does not provide the same information as checking both.
What can affect your results?
Dehydration, intense exercise, a recent meat-heavy meal and some medicines or supplements can affect creatinine. Tell your doctor about recent illness and everything you take, including non-prescription products. An unexpected result should be investigated rather than automatically blamed on food or exercise.
Follow the laboratory’s preparation instructions, because these may depend on the other tests being done at the same time. Do not stop prescribed medicines or make unusual changes to your diet before testing unless your doctor has advised you to do so.
Why changes over time matter
Your previous results help your doctor understand what is usual for you. Small differences between tests may reflect normal variation, while a larger or continuing change needs assessment. Looking at the pattern is often more useful than comparing your result with someone else’s.
Ask whether a repeat test is needed and how soon it should happen. The three-month period used to establish chronic kidney disease is not a reason to delay assessment of a sudden deterioration. Your doctor may need to investigate much sooner if acute kidney injury is possible.
What should you do after an abnormal result?
Arrange a review and bring earlier blood and urine reports, your medicine list and details of any recent illness. Your doctor can explain whether the result needs repeating, whether more tests are needed and whether treatment or medicine doses should change.
Seek urgent medical assessment if you are passing much less urine than usual, develop new breathlessness or become unusually confused or drowsy. These symptoms need attention even if you are waiting for a repeat test or a routine appointment.