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Understanding Your Kidney Blood Test: 3 Important Things to Know

Understanding your Kidney blood test: 3 Important things to know
Understanding your Kidney blood test

In understanding your Kidney blood test: 3 important things to know will help empower you to preserve your kidney function and motivate you to help prevent future worsening that function. The Glomerular filtration rate (GFR) blood test is an important measure of kidney function but it is not the only important measure used to check how your kidneys are doing. Urine tests and imaging tests are also very important. For the purpose of truly understanding Your Kidney Blood Test: 3 Important Things to Know will always include the GFR.

Know your Diagnosis

If you have been diagnosed with any of the following, then you should 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
  • Any Cancer that requires chemotherapy
  • Nephrotic syndrome
  • Glomerulonephritis

If you have also ever had a history of acute kidney injury (AKI), you should know your GFR and any changes thereof, 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.

Understanding the GFR: The Basics

For the understanding your Kidney blood test: 3 important 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 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 filtering is one of the biggest jobs the kidneys do, but remember that their entire job description is even more. 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, preventing build up of acid, helping to process some medications, and more.

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 (e.g. ”>60”) like many labs do and not an actual number. As you can imagine >60 (“greater than 60”) can mean many things: it can mean 61 or it can mean 120!

The GFR has some limitations: Context is important

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 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! Stage 3 is divided into 3A & 3B!

Understanding your Kidney blood test: 3 Important things to know!

Understanding your Kidney blood test

To ensure that you are properly understanding your Kidney blood test: 3 important things to know below will be necessary :

  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 important truth is that if your blood test is shown as “normal” on most lab test reports, it means that you do not have stage 3A or a worse stage of chronic kidney disease (CKD). Therefore in understanding your Kidney blood test: 3 important things to know are dependent on each other like #2 below 
  2. GFR in CKD is not intended to be interpreted by its self. It should be accompanied by a)urine testing, b) kidney pictures and c) knowledge of how much urine you are making. These 3 things show the remainder of whole story of your kidneys- the portions that the GFR cannot tell! All 3 together plus the GFR should be interpreted with time in mind! For example if today you have produced remarkably less urine than a month ago, then your doctor needs to know immediately!
  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 kidney function is worsening faster than it is supposed to, this may prompt a review, new tests, medication changes, a change in treatment etc. in addition, changes in your GFR are also important as people with chronic kidney disease are at a higher risk of acute kidney injury (AKI). Example of important discerning examples: A GFR of 62 may look ok but if it was 179 just last week there is a problem as an accompanying creatinine rise from 0.4 to 1.0 may look ok to the lab is consistent with a Stage 2 Acute Kidney injury (AKI). Unlike CKD, AKI has only 3 stages!

The Stages of Chronic Kidney Disease (CKD) Explained.

“Chronic” in Chronic Kidney Disease (CKD) means a duration of three (3) calendar months or longer. At the heart of understanding your Kidney blood test: 3 Important things to know intertwine the stages of CKD and in so doing allows you to apply the crucial points to your unique 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:

  1. 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! 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!
  2. 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.
  3. 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
  4. 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!
  5. 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.

For a longer version of this page with more explanations, please visit our related page on Decoding the GFR!

DISCLAIMER: Please remember that this page 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 is not medical advice and does not replace your doctor’s or medical provider’s expertise nor opinion. You must discuss all your treatment with your medical provider and follow their advice as your doctor and healthcare team possess the necessary details of your unique condition.

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