Renal Function Panel: Know Your Numbers

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The renal function panel (aka renal function tests or RFTs) is one of the blood tests your physician will order when you have kidney disease. This test is reviewed by your doctor and renal dietitian.

Your labs can provide your healthcare providers with details of what is going on inside your body- whether you realize it or not. Let’s dive into exactly what an adult renal function panel includes.

Preparing for Your Renal Panel

As with most tests, preparation can be a very important part of tests. This includes lab tests!

When Should I Get a Renal Function Panel?

Your doctor or kidney specialist will determine whether or not you need a renal function panel. Some of the other health conditions that may trigger a physician to order it include;

• High blood pressure
• High blood sugars or a diagnosis of diabetes
• Cardiovascular disease
• Obesity
• High cholesterol

Additionally, your doctor may order the testing if you have a family history of kidney disease or show signs and symptoms of kidney issues. Some symptoms can include;

• Swelling around the hands, feet, ankles, or face
• Changes in your urine like decreased frequency, presence of foam or blood
• Pain to your mid-lower back where the kidneys are located

How Long Does it Take to Get the Results?

Generally, the test results are reported within 24 hours. Many doctors, however, will require “signing off” the results prior to passing them on to the patient.

What Type of Sample is Required?

A renal function panel requires a blood sample. This is taken from a vein in your arm by a phlebotomist. This may be done in your doctors office or at a separate lab location.

Do I Need to Fast Beforehand?

Your doctor will instruct you on whether or not you need to fast. This is generally not required for the kidney function test, but could be ordered for other lab testing you may also be getting at the same time.

To fast before a blood test, you do not eat any food for the 8 to 12 hours before the appointment time. It’s important you still drink plenty of water before as dehydration can negatively affect your renal function test results.

Can Fasting Too Long Affect the Results?

Fasting for an excessive period can affect your results by causing a lower glucose level. 

If you don’t have enough water, that can also cause abnormalities in your eGFR, sodium, and chloride levels.

Renal Function Panel Test Details

If you have told your doctor about a family history of kidney disease, or you are already aware of your own diagnosis of kidney disease, you are likely to have a renal panel or renal function panel in your blood test results.

These results can be drawn anywhere from monthly to annually (once per year). The timing will be based on your nephrologist or physician’s orders. Many doctors are open to having additional labs drawn when requested – but be prepared to put in work if you want to get your renal function panel drawn more frequently.

Waste Products

Blood Urea Nitrogen

Blood urea nitrogen – otherwise known as urea nitrogen or BUN – is a measurement of protein breakdown in the body. 

BUN is generally below 20 mg/dL but will often rise when there is kidney damage. This is because the kidneys are unable to keep up with eliminating excessive waste.

BUN may trend around 75 mg/dL when on dialysis.

A low-protein diet can help in reducing BUN for those not on dialysis. However, if done improperly it can increase the risk of protein-energy wasting and malnutrition. This can then increase inflammation and potentially increase kidney damage. Ketoanalogues can also help lower BUN levels when paired with a low protein diet.

Creatinine

Creatinine is a waste product from normal muscle metabolism and breakdown. It is not directly related to dietary protein intake over time. One study found that eating meat prior to a blood draw for creatinine testing, creatinine was falsely higher.

A normal serum creatinine level is between 0.6 – 1.2 mg/dL for males and 0.5 – 1.1 mg/dL for females. However, it can vary for many reasons, including gender, age, and activity level.

Creatinine will increase as kidney function decreases. This is because with CKD, the kidneys aren’t eliminating waste from the body. 

Creatinine levels measured in chronic kidney disease can range anywhere from 2.0-15.0 mg/dL depending on the stage and other health conditions.

While creatinine is not directly related to nutrition, finding other culprits that impact your kidney health may help to lower or stabilize creatinine levels. This can come from dietary changes that help promote a healthy kidney!

Protein in the Blood

Albumin

Albumin is a protein that is made in the liver. Your serum albumin is a measurement of how much albumin is in your blood. It was previously thought was that albumin would indicate how much protein you are eating. We now know that it is much more than just that.

Normal albumin will range from about 3.4 – 5.0 g/dL. As it can signal problems with inflammation, it will decrease when there is more inflammation.

If you’ve been hospitalized and have access to your labs, take a look at your albumin before, during, and after your hospitalization. When a person is hospitalized, they go through a lot that can be inflammatory. Once they get better the albumin can increase, indicating the healing process.

Evidence shows that following a low-protein diet does not significantly alter albumin levels.

Electrolytes

Sodium

Sodium is the most common particle in our blood outside of our cells. It helps with muscle function, acid-base balance, cellular balance, and osmotic pressure of body fluids.

Many associate sodium levels with the amount of salt in the diet. However, it is more than just that.

Your blood test result is not a reliable measurement of your sodium intake. It is a better marker for your fluid balance.

The blood serum sodium levels are typically between 135 – 145 mEq/L. If you experience edema or swelling of extremities with excessive fluids, you may see a slightly lower sodium level. Additionally, sodium levels may also be falsely low if you drink a lot of water right before your blood draw.

A sodium level above the normal range can be a sign of dehydration.

It’s been thought before that if your sodium is out of range that you should eat more/less salt. That may not necessarily be the case and may cause more issues. Before making drastic changes in your diet, it’s best to consult with a registered dietitian to help assess all factors that may be causing an out-of-range sodium level.

Potassium

Potassium is the third most abundant mineral in our bodies. It acts as an electrolyte and helps with nerve conductivity, muscle contraction, and fluid balance. 

The potassium level found in your renal function panel or basic metabolic panel is generally between 3.5 – 5.0 mEq/L.

High- and low-potassium values should be reviewed promptly with your physician and healthcare team as potassium plays an important role in our heart function.

If your potassium levels are consistently above 5.0, you may need to follow a low-potassium diet.

Bicarbonate

Your serum bicarbonate (or carbon dioxide or CO2) is related to the acid-base balance, or pH levels, of your body. With kidney issues, the bicarbonate levels tend to decline. As a result, the body then leans towards a more acidic state. 

Normal bicarbonate levels in the blood are approximately 20 – 29 mEq/L.

Low bicarbonate levels have been associated with an increased risk of kidney problems. This is caused by metabolic acidosis, a common outcome of prolonged kidney damage.

By paying attention to the potential renal acid load in your diet, you may be able to keep your kidney function with healthy diet changes.

Chloride

Chloride is a negatively charged electrolyte. It helps to balance your fluids as well as your acid-base balance.

The blood serum levels of chloride are generally between 98 – 107 mEq/L. 

A low level of chloride may indicate overhydration or be a result of excessive vomiting. Low chloride can also be due to other health issues like diabetic ketoacidosis, aldosterone deficiency, Addison disease, emphysema, or chronic lung diseases. 

High levels of chloride can indicate dehydration. However, it can also indicate health issues including kidney disease due to the imbalance of the acid-base balance that the kidney helps with.

Minerals

Phosphorus

Phosphorus is another mineral found in our body. It’s actually the second highest in quantity, behind calcium.

Phosphorus does plenty of things to help keep us healthy, such as manage how your body uses energy, build strong bones and teeth, regulate vitamin use, and help with muscle contraction (including our heart!).

Blood serum levels of phosphorus should generally be approximately 2.5 – 4.5 mg/dL, but ranges may differ depending on the individual. Some nephrology clinics have different ranges to accommodate for the expected higher ranges of phosphorus in late-stage CKD, which may look closer to 3.0 – 5.0 mg/dL.

Even though there is some “forgiveness” with slightly higher phosphorus levels, the Kidney Disease International Outcomes Guidelines (KDIGO) still express the need to focus on striving for phosphorus within the normal range to prevent increased risk of death.

It will be important to follow a low phosphorus diet if phosphorus is above 4.5. Phosphorus binders may also be prescribed.

Calcium

Calcium is the number one mineral stored in our body. It helps with many things including bone health and muscle contraction. General calcium levels are between 8.5 – 10.2 mg/dL.

As our kidneys help regulate our bone health, calcium becomes an important value to monitor with kidney disease.

With many people with CKD, calcium can trend out of range. Calcium can either go above the healthy range or below. This often leads to either including or avoiding calcium supplements, depending on your labs and other health conditions.

Never take calcium supplements without first discussing them with your nephrologist. Too much calcium can lead to calcification in your soft tissues. As a result, it can lead to an increased risk of heart attack and stroke.

Energy

Glucose

Glucose is considered the primary source of energy for our body. It is taken from the blood into the cells with the help of insulin. It’s important the level of glucose in our body doesn’t get too low or too high.

The normal range for glucose is broken down into two categories: fasting or non-fasting. Non-fasting just means you ate something in the hours or day before your renal panel. Again, it’s important to find out if you should be fasting or not. A renal function panel alone does not generally require fasting.

Fasting glucose is between 70 – 100 mg/dL. For non-fasting glucose, it’s normal to have a level at or below 200 mg/dL.

If you have diabetes, your glucose goals may be different than these reference ranges. Learn more about the renal diabetic diet here.

Kidney Function Tests and Calculations

Glomerular Filtration Rate

The glomerular filtration rate, or GFR, is a measurement of your kidney function of blood filtration. This is a calculation based on your gender, age, size, and creatinine in your blood. This is one of the most common tests to assess your kidney function.

A normal GFR is above 90. Some lab reports will look for a GFR of at least 60, as the function will naturally decline as we age.

GFR is associated with stages of kidney disease. Kidney failure is associated with a GFR below 15. However, not just one low value will be enough to confirm kidney issues.

A low GFR for three months can indicate kidney disease along with a diagnosis from a physician. Calculate your eGFR here.

Urea-to-Creatinine Ratio

Also known as the BUN-to-creatinine ratio or BCR, this is a calculator to evaluate waste removal. The reference range for this ratio is anywhere from 6 – 22.

Since it is a ratio, changes in either Blood Urea Nitrogen or Urea will affect this level. Increased levels can be caused by congestive heart failure or dehydration. Decreased levels can be related to liver disease or malnutrition.

Anion Gap

The anion gap is a calculation of your electrolytes: sodium, potassium, chloride, and bicarbonate. 

The anion gap calculation is:

[Sodium (mEq/L) + Potassium (mEq/L)] – [Chloride (mEq/L) + Bicarbonate (mEq/L)] = Anion Gap

The reference range for the anion gap is 8 – 16 mEq/L.

The anion gap calculation can be a factor when evaluating for metabolic acidosis for this reason. However, it is important to look at each electrolyte in the equation when evaluating reasons for high- or low levels.

Renal Function Panel Normal Values Chart

Below is a table of the reference ranges for tests included in the renal function panel. There is also a column for the abbreviations you may see.

Test	Abbreviation	Reference Range
Sodium	Na	135 – 145 mEq/L
Potassium	K	3.0 – 5.0 mEq/L
Chloride	Cl	98 – 107 mEq/L
Bicarbonate	CO2	20 – 29 mEq/L
Phosphorus	P	2.5 – 4.5 mg/dL
Calcium	Ca	8.5 – 10.2 mg/dL
Glucose	Glu	70 – 100 mg/dL fasting<200 mg/dL non-fasting
Blood Urea Nitrogen	BUN	7 – 20 mg/dL
Creatinine	Cr	Adult males: 0.6 – 1.2 mg/dLAdult females: 0.5 – 1.1 mg/dL
Albumin	Alb	3.4 – 5.0 mg/dL
Estimated Glomerular Filtration Rate	eGFR or GFR	>60
Anion Gap	AG	8 – 16 mEq/L
Blood Urea Nitrogen-Creatinine Ratio	BCR	6 – 22

It’s important to know that the reference ranges may be slightly different on your own test results. Discuss any questions related to your own renal panel results or reference ranges with your physician.

Renal Function Panel vs. BMP

While similar, a renal function panel is slightly different from a BMP or basic metabolic panel. Here is a comparison chart between the two tests.

What Other Lab Tests Besides the Renal Panel May Be Needed?

Depending on your own health history, diagnosis, and situation, there can be other types of tests that are done in addition to the renal function test.

Cystatin C

Cystatic C is a protein made in the body and used to assess kidney function. With good kidney function, the level of cystatin C remains balanced. 

It’s seen as a better marker for kidney issues compared to creatinine as it is not easily influenced by muscle mass (like creatinine is).

For those with kidney issues, cystatin C can build up. Many GFR calculators ask for cystatin C levels to confirm the kidney function or stage of CKD. 

Cystatin C is not part of the renal panel, but may be ordered by the doctor if labs in the renal panel are abnormal or suggest kidney damage.

Similar to creatinine, cystatin C levels will be different based on age. The reference range for adults under the age of 50 is between 0.53 – 0.92 mg/L. For adults over the age of 50, the reference range is between 0.58 – 1.02 mg/L.

Parathyroid Hormone

The parathyroid hormone (PTH) levels are measured because the kidneys directly tell the body how much of the hormone is needed. PTH is responsible for balancing the calcium and phosphorus levels in our blood and body.

A normal intact PTH (or iPTH) level is between 10 – 65 pg/mL.

When the kidneys aren’t working well, this number tends to increase. This can lead to up to ten times as high as the normal range. This increase is expected in kidney disease. While it may not return to the normal range, PTH should be monitored and stabilized.

One of the labs that can greatly influence PTH is phosphorus. High phosphorus can cause higher PTH levels. 

Many people with high PTH are encouraged to follow a low phosphorus diet and take phosphorus binders as prescribed.

Vitamin D

We get vitamin D is from the sun and our diet. It is activated by our kidneys.

Normal vitamin D levels are at least above 20 ng/mL. Vitamin D toxicity can occur if levels are over 100 ng/mL.

When kidneys aren’t working as well, vitamin D levels tend to decline. KDIGO guidelines have addressed that vitamin D deficiency is common in CKD. Therefore, many people with kidney disease supplement with vitamin D.

Appropriate dosing is very important as it is also unhealthy to have excessively high vitamin D levels in the body. Always consult with your nephrologist and renal dietitian about the amount of vitamin D you should be taking.

Additional Tests for Kidney Health

Some of the tests can include;

• Hemoglobin A1c for blood sugar control
• Lipid Panel
• Complete Blood Count (CBC)
• Iron Panel
• Thyroid Panel

Other Types of Kidney Tests

Depending on your lab results, your doctor may order additional tests to assess your kidney function.

You may have an ultrasound or CT scan of your kidneys. This will give the doctor a picture of your kidneys and urinary tract. It will help show physical signs of kidney problems, such as size, kidney stones, tumors, or other abnormalities.

Your doctor may also want a kidney biopsy. This procedure requires a tiny sample of your kidney tissue. The sample is studied under a microscope. A kidney biopsoty may not be necessary depending on your labs. 

Many doctors will not order a biopsy if other tests have already confirmed a certain diagnosis, or there would be no benefit in the procedure.

Finally, your doctor may also order a urine test, or urinalysis. This is a test in which you provide a small sample of urine. The sample is analyzed visually, with a microscope, and with a dipstick.

A urinalysis can check for creatinine clearance, protein leaking, glucose, white blood cells, and crystals among other issues.

After You Get Your Lab Results

A Renal Function Panel is Not Diagnostic Itself

Lab results are a snapshot of what is happening at the time of your blood draw. Therefore, one test result cannot provide a diagnosis of CKD.

Your labs will change from result to result. It’s important to know that just one result that is out of range may not tell much. Getting retested is important to confirm any outlier. 

Track the patterns and changes to get a better feel for how your body and kidneys are doing. Your physician will likely order follow-up labs for confirmation and diagnosis if a lab result is outside of the expected range.

Make a Plan

Review your results and ask as many questions as needed for you to feel comfortable with your results. You may or may not have all of these labs in your results – your physician will determine which labs are necessary. 

Discuss any labs of concern with your doctor, including what should be done to improve them. This is also a good time to talk about when you’ll be getting labs drawn again.

Learn more about questions to ask your kidney specialist here.

Seek Out Specialists

Depending on your results, you may benefit from a specialist to help you in a certain area. Registered dietitians help people by providing further explanations of nutrition-related labs and how your diet can impact your health. 

Working privately with a dietitian will give you more concrete answers on what your own lab results mean and how your diet can help improve your levels. This isn’t just for dialysis. Dietitians help all stages of CKD, from stage 1 to stage 3 and beyond!

Watch the Video About The Renal Function Panel

Summary

When looking at your renal function panel, it’s important to know that it’s a snapshot of your health. Lab tests alone do not provide a diagnosis and cannot tell the whole story.

Speak with your doctor to see if a renal function panel would be helpful for your health goals. While using this article as a reference for the different labs, it’s important to discuss your results with your doctor.

When you want to make changes to your diet to help with your lab test results, ask your doctor for a referral to a dietitian. They can provide you with a deeper understanding of your own lab test results and provide you with personalized recommendations.