Decoding your GFR Kidney blood test: 3 Crucial things to know

In understanding & decoding your GFR Kidney blood test: 3 Crucial things to know will help empower you to help preserve your current kidney function and motivate you to help prevent future worsening of your kidney function. These are eye opening and necessary pearls for everyone with kidney disease and everyone at risk of kidney disease to know! This Glomerular filtration rate (GFR) blood test is an important measure of kidney function but not the only important measure used to evaluate your kidneys: urine and imaging are also very important.

Table of Contents

Do You Know Your Diagnosis?

If you have been diagnosed with any of the following, then it is important to know your GFR results:

Chronic kidney disease (CKD)
Kidney stones
Kidney cysts
Autosomal dominant polycystic kidney disease (ADPKD)
Hematuria
Proteinuria
Sickle cell disease
Kidney cancer
Kidney tumors
Nephrotic syndrome
Glomerulonephritis
Any Cancer that requires chemotherapy as some chemotherapy medications can interfere with kidney function

You also want to know future GFR results to help track your progress and stage of disease.

If you have also ever had a history of acute kidney injury (AKI), decoding your GFR Kidney blood test: 3 Crucial things to know are also very important. If you have ever had AKI, the reason you should know your GFR and any changes thereof, is because unfortunately, AKI increases your future risk of chronic kidney disease & kidney failure. Learn more about acute kidney injury (AKI) from the National Kidney Foundation and here on our site!

If you have ever been diagnosed with diabetes or hypertension, you should also know your GFR because these two conditions are the leading causes of chronic kidney disease (CKD) in the US. If you have cancer then your GFR is also important as some chemotherapy medications can affect the kidneys and so the GFR is one of the routine tests used for monitoring many patients with cancer.

Decoding the GFR: The Basics

For the decoding your GFR Kidney blood test: 3 Crucial things to know build upon the knowledge of what “GFR” actually stands for.

GFR stands for glomerular filtration rate which is a measure of how well your kidneys are filtering the blood sent to them. The filtering is one of the biggest jobs of the kidneys do. The GFR is an estimation of your kidney function that is calculated using a blood test called the creatinine and other factors including gender. The lower the GFR, the worse your kidneys are doing/functioning. The GFR moves in the opposite direction of the creatinine: The higher the creatinine, the worse your kidney function!

The glomerular filtration rate or GFR you receive in your routine blood test may be a bit confusing especially when, sometimes, it is given as a kind of range of “>60″ like many labs do instead of an actual number. As you can imagine >60 (“greater than 60”) can mean many things: it can mean 61 or it can mean 120!

GFR is a measure used to stage & monitor Chronic Kidney Disease (CKD). The “Chronic” in this particular medical term means that it has been going on for three (3) months or longer. There are some instances when the GFR is not the best true measure of kidney function like during acute kidney injury (AKI) When fluctuations in the creatinine and its limitations make the GFR less reliable under those evolving circumstances.

Therefore, your doctor may not be able to tell you your true steady GFR if you are experiencing AKI: he or she will have a to wait until the AKI has resolved and you have stabilized to know your true steady/stable GFR. You will therefore notice that the GFR is chiefly used in the evaluation and monitoring of chronic kidney disease (CKD) and in routine lab tests.

The entire job description of the kidneys is more fancy and complicated than just filtering blood, so you might notice that your doctor orders other tests too. The job of the awesome kidneys also include controlling blood pressure, getting rid of excess fluid, getting rid of toxins/waste, producing the hormone that makes red blood cells, making vitamin D (the last step of the process), regulating calcium and regulating phosphorus in your body

The GFR in Chronic Kidney Disease (CKD)

The GFR is the number that is used to tell you the stage of chronic kidney disease you have! Chronic Kidney Disease (CKD) is not like cancer that has 4 stages: Chronic Kidney Disease (CKD) has five (5) stages! Plus to make it more complicated (because the kidneys are fancy like that): Stage 3 is divided into 3A & 3B!

Important GFR Bulletin!

The American Society of Nephrology (ASN) and The National Kidney Foundation (NKF) no longer recommend including the race modifier for calculation of the GFR because the race modifier was causing a few issues. The race modifier was resulting in later referrals for specialist care and also sometimes causing chronic kidney disease (CKD) to be hidden on lab reports and shown as “normal” (Fly under the radar) in Black people even though they are 3.5 times more likely than White persons to have kidney failure.

For example, 2 blood tubes are sent to the lab with the same sample, from a male, age (75) and creatinine (1.3mg/dL):

Tube 1 is labeled: Race White and
Tube 2 is labeled: Race Black

The GFR for Tube 1 would be reported as 57 and Stage 3A CKD and therefore trigger action for further medical care…

But the GFR for Tube 2 would be reported as 69 and therefore show as normal even though the SAME sample was used for both tubes. The lab and the provider do not know that the person who gave the sample has urine positive for blood and protein because no urine sample was sent. Therefore with the race modifier calculation of GFR, Black patients were having their kidney disease detected later and receiving delayed referrals for kidney care, kidney transplant and preparation for dialysis compared to other races even though the Black race is disproportionately more affected by kidney failure (at higher rates).

The process of ensuring that lab reports no longer show a race-modified GFR for African-American/Black race is going to take some time so you may still see a GFR number with race modifier on your lab report until the entire health system is aware of and implements the new recommendations. In the interim, read more about the controversy by clicking here to visit The National Kidney Foundation’s site!

Decoding your GFR Kidney blood test: 3 Crucial things to know!

Decoding your GFR Kidney blood test: 3 Crucial things to know are below:

Decoding your GFR Kidney blood test: 3 Crucial things to know #1!
- There is a misconception or common thinking that there is no kidney disease if your GFR blood test is shown as “normal” on your lab report. The truth is that the if your blood test is shown as normal on most lab test reports, it is essentially saying that you do not have stage 3A or any worse stages of chronic kidney disease. Therefore in decoding your GFR Kidney blood test: 3 Crucial things to know depend on each other so please read crucial thing #2 below
Decoding your GFR Kidney blood test: 3 Crucial things to know #2!
- GFR in CKD is not intended to be interpreted by its lonesome self. It should be accompanied by urine testing, kidney pictures and a good idea of how much urine you are making. These 3 things show the remainder of whole story of what is going on with your kidneys- the bit the GFR cannot tell! All 3 together plus the GFR should be interpreted with time in the back of your mind! For example if you start producing less urine Like 2 cups per day instead of 1 gallon per day that you used to make a month ago, then your doctor needs to know right a way!
Decoding your GFR Kidney blood test: 3 Crucial things to know #3
- The GFR should be trended, paired with the creatinine, and compared to themselves at different moments in time so that your doctor can know if your kidney function is worsening. If your doctor sees that your kidney function is worsening faster than it is supposed to, this worsening may prompt a review, new tests, medication changes, a change in treatment etc. Changes in your GFR is also important for another reason: people with chronic kidney disease are at a higher risk of acute kidney injury (AKI).
- Therefore, for example, A GFR of 62 may look ok BUT if it was 179 just last month? Then “Houston, we have a problem!” Likewise a creatinine of 1.0 may look ok to the lab but if your creatinine was 0.4 just last week: we have a problem because that scenario looks and quacks like a Stage 2 Acute Kidney injury (AKI) and unlike CKD, AKI has only 3 stages!

Now Some Additional Pearls regarding Decoding your GFR Kidney blood test: 3 Crucial things to know: #3:

Urine Testing & Imaging

Decoding your GFR Kidney blood test: 3 Crucial things to KNOW hinge on The Big Picture: Blood test/GFR is not the only measure of how your kidneys are doing: there are 3 other “Big deal” tests/measurements! Urine Test for protein, blood, crystals and other abnormalities, Kidney pictures or imaging, and good ole urine volume measurement! Urine test: they show what your kidneys are making or what your kidneys are giving a “free pass” to go through when they should not be giving free passes: things like protein, blood, fat (lipids), abnormal cells, and casts that aren’t supposed to be in the urine! If large amounts of blood and/or protein or fat are found in your urine, the most common cause is sick kidneys.
- However, overproduction of abnormal proteins in your body can also cause spillage of protein into urine (this overproduction can be die to some hematologic cancer, hematologic disorders or some inflammatory disorders).
Regarding blood in the urine, sick kidneys can be the culprit but Tumors, kidney stones and other abnormalities in the urinary tract can also cause blood and other cells to get into the urine. Your nephrologist can help tell the difference of what causes the blood in urine by special tests and by looking at your urine under the microscope! When blood comes from sick kidneys, the red blood cells look funny or dysmorphic and some even look like Mickey mouse: seriously they have little Mickey Mouse ears! and cells that aren’t supposed to be there etc.
Remember that your kidneys are rock stars so they are awesome at compensating to make your blood look good even when they themselves are sick/not well or hurting a bit. So you have to understand that it is not only about the GFR blood test result, its about what the pee/urine looks like to the lab chemically and under the microscope PLUS what the kidneys look like structurally on imaging: ultrasound, CT etc! Following your doctors’ instructions to have your Urine tested and kidney pictures taken is therefore of utmost importance!

Now all of that being said, below is the frank, down to earth simple explanation of the different stages of chronic kidney disease (CKD) spoken of at your doctors’ office!

The Stages of Chronic Kidney Disease (CKD) Explained.

Oh, by the way, the “Chronic” in Chronic Kidney Disease (CKD) means it’s been going on for three (3) calendar months or longer). At the heart of Decoding your GFR Kidney blood test: 3 Crucial things to know intertwine the stages of CKD and in so doing allows you to apply the crucial points to your own case. Cancer has 4 stages, acute kidney injury has 3 stages. Chronic Kidney Disease (CKD) is different: CKD has 5 stages & this is what the stages roughly mean:

CKD Stage 1: GFR 90 and higher: Your blood test numbers look excellent and perfectly normal to the lab and to any eye reading blood results only without looking at your whole chart… but there is more beneath the surface! ANY ONE or a combination of the following is happening: You are spilling protein in your urine, blood in your urine, you have kidney crystals or stones OR there is a structural/physical problem with your kidney or kidneys. Structural problems may include cysts, strictures, tumors, swelling of kidneys, a small kidney etc.
- Remember that your kidneys are rock stars, so they are awesome at compensating to make your blood look good even when they themselves are sick/not well or hurting a bit. So you have to understand that it is not only about the blood test result: it’s about what the pee/urine looks like to the lab chemically and under the microscope PLUS what your kidneys look like structurally on imaging: ultrasound, CT scan etc. ! Following your doctors’ instructions to have your Urine tested and kidney pictures taken is therefore of utmost importance!
CKD Stage 2: GFR 60 to 89: Your blood test results look good: the lab wont even flag it as abnormal! But again, like stage 1 there is more beneath the surface! ANY ONE or a combination of the following is happening: You are spilling protein in your urine, blood in your urine, you have kidney crystals or stones OR there is a structural/physical problem with your kidney or kidneys. As mentioned above, Structural problems may include cysts, strictures, tumors, swelling of kidneys, a small kidney etc. However, like with stage 1, your kidneys are awesome at compensating and therefore they are good at making the blood look good even though something else is going on.
CKD Stage 3A: GFR 45 to 59: Hold on now! Something is not right and anyone can see that your numbers are not normal: your nurse can see, your PCP and even you can see it flagged if you look at the report! At Stage 3A, it is crucial to be in the know. You need to find out what’s wrong or what caused your kidney numbers to dip down to this range. Knowing helps so you can preserve your kidneys and help protect the GFR number from worsening because worse is bad and at Stage 3A, you are NOT far away from Stage 3B. This is a good time to get very disciplined with your diet, taking the meds your doctor prescribed, watching your diet, & avoiding the over-the-counter medications that can harm your kidneys
CKD Stage 4: GFR 15 to 29: This is not good AT ALL. Your outcomes/chance of survival will be better if you take your condition very seriously and carefully follow the instructions of your doctor. When your GFR falls below 20, the standard of care recommends referral for evaluation for kidney transplant, and discussion and preparation for a method of dialysis: hemodialysis or peritoneal dialysis. The reason for the referral when your GFR falls below 20 is that the processes of preparation for Transplant and Dialysis take time! For example, The safest and most efficient access for hemodialysis which is an AV fistula, takes approximately 3-4 months to get ready!
CKD Stage 5: GFR less than 15 Something is very very very wrong with your kidneys and you should be in contact with your doctor frequently for monitoring and for life-sustaining long-term solutions because there is a real risk of the kidneys losing their last bit of crucial function and when those functions are completely or partially lost, serious life threatening illness or death will occur without treatment. Scary things can happen like difficulty breathing due to excess fluids accumulating in the lungs (as the kidneys cant get rid of that fluid anymore), a very, very high blood pressure with consequences like heart attack or stroke, sleepiness or confusion die to accumulation of toxins (a good marker is another sister test: the BUN or urea being super high- again because the kidneys cannot remove it anymore!), heart arrhythmias from the potassium level being dangerously high (again because the kidneys can’t get rid of it as usual), and of her potential problems.

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DISCLAIMER: Please remember that this page “Decoding your GFR Kidney blood test: 3 Crucial things to know” is not medical advice. There are multiple factors unique to your particular case and days, weeks, months or years of results, treatment and perspective that only your doctor and health team have access to regarding your case. The content on this webpage and this website is for information to help you in comprehending a concept and help start the conversation about kidney disease in a way that increases your awareness and helps empower you to make healthy choices.

The explanation on this webpage is done in real-life everyday terms without medical jargon as best as possible. The information on this page does not replace your doctor’s expertise nor opinion and you should always talk to your doctor! All cases used as examples are fictitious but may employ application of the real MDRD equations for GFR!