Renal Lab Values: What You Need to Know from a Renal Dietitian

Renal Lab Values: What You Need to Know from a Renal Dietitian

Understanding your renal labs is the best place to start in understanding how food can affect your kidney disease.

Learning how to review your labs and track them is no small task! That’s where I come in. My name is Candace Mooney and I’m a registered dietitian and board certified specialist in renal nutrition.

I’ll walk you through your kidney function labs and what they mean. Then, I’ll take you through the labs I like to monitor when working with private clients and explain why they should be important to you. 

Let’s get started!

Basic Kidney Functions

Your kidneys play numerous vital roles in your body!

  1. They control the mineral composition of your blood.
  2. They control the volume of your blood by producing urine.
  3. They remove metabolic wastes.
  4. They maintain acid-base balance.
  5. They help regulate hormones.
  6. They even break down insulin.

Your lab values help show which of these functions are working well and which ones could use some help!

Common Kidney Function Labs: Creatinine, Blood Urea Nitrogen, Cystatin C, Glomerular Filtration Rate, and Albuminuria

Measuring your blood via waste products is one of the most common ways to assess kidney function because waste products in your blood increase as kidney function declines. 

Creatinine (Cr)

Normal Values: 0.6 to 1.5 mg/dl. (1)

Cr is produced when protein is broken down either from the food you eat or from your muscle tissue. 

The Cr levels increase as kidney function declines but can be heavily influenced by other factors like your:

  1. Muscle mass
  2. Hydration status
  3. Activity level
  4. Inflammation or infection
  5. Malnutrition.

These are all things to consider when evaluating this lab value.

Blood Urea Nitrogen (BUN)

Normal Values: 5 to 20 mg/dl. (1)

BUN is a waste product from the breakdown of the protein made within our cells, not just the protein from our diet. BUN measures how much urea nitrogen is in your blood that your kidneys would normally eliminate in your urine. 

The BUN level increases as kidney function declines.

Cystatin C

Cystatin C is thought to be a better marker than creatinine for people that are overweight, have more muscle mass, or are elderly. It is less influenced by protein in your diet, activity level, and your muscle mass. (2)

Cystatin C increases as kidney function declines and is used in an equation to determine your kidney function. (3)

Glomerular Filtration Rate (GFR) 

GFR is a calculation using waste products (most commonly creatinine), your age and gender to estimate how well your kidneys are filtering and maintaining your blood contents. 

To be diagnosed with stage 3-5 kidney disease, you typically have a GFR of less than 60 for at least 3 months. (3)

Your GFR indicates different stages of kidney disease. As the number stage increases, kidney function declines. This chart shows how GFR can measure kidney disease.

Stages of kidney disease based on GFR showing percent of kidney function.
(4)

GFR also decreases as you age so a normal GFR for someone older than 70 is not a normal GFR for someone that is 20 years old. (5)

AgeAverage Measured GFR (mL/min/1.73m2)
20-29116
30-39107
40-4999
50-5993
60-6985
70+75
Table Sourced from NHANES III

Albuminuria

Normal values: 0-30 mg/g

Albuminuria is a measure of how much protein is being spilled into your urine. It is typically reported as the urine Albumin to Creatinine ratio (uACR) on your urine test. (6)

Your goal would be to decrease or eliminate any protein in your urine to improve your health and decrease the damage to your kidneys. 

Nutrition Recommendations:

Choosing a lower sodium and lower protein meal with an emphasis on reducing animal protein reduces protein leaking into your urine. (7)

Common Conditions with Lab Values

Metabolic Acidosis – Bicarbonate

Bicarbonate (CO2) in your blood measures your blood pH. Kidneys that aren’t working properly have a hard time excreting acid in your urine so your serum bicarbonate levels can be low with kidney disease. (8)

Normal levels are 22-29 mEq/L but ideal levels are 24-26. Lower levels mean your blood is too acidic. 

Nutrition Recommendations:

Protein (animal protein) typically decreases your bicarbonate level making your blood more acidic. Plants typically have the opposite effect. This can be described by the Potential Renal Acid Load of foods. 

This topic is discussed in depth in our blog, Potential Renal Acid Load and Its Impact on Kidney Disease: Including PRAL Food Chart, List, and Calculator.

Anemia – Hgb, Ferritin, TSAT, B Vitamins 

Anemia occurs when there is a deficiency in red blood cells or the amount of hemoglobin. Some symptoms of anemia are shortness of breath, tiredness, weakness or paleness. (9, 10)

Anemia is very common with kidney disease because when your kidneys aren’t functioning at 100%, they don’t release the hormone that tells our bones to make red blood cells.

It’s important to note that you can have anemia simply because your kidneys are not functioning properly. Adjusting your diet may not have any effect on these labs. You may need an erythropoietin stimulating agent to help with red blood production. Your doctor will know best.

Knowing the following numbers can help you determine what foods or what supplements may be appropriate with the approval of your doctor. 

Hemoglobin (Hgb) normal range: 12-17 g/dL. Hemoglobin is a protein found in your red blood cells and is the marker used to diagnose anemia.

Iron is used to make hemoglobin so measuring iron with Ferritin and TSAT can determine if your iron level is contributing to anemia. 

Ferritin: <100 mg/dl shows depleted iron stores. This value could be elevated in inflammation. 

Transferrin Saturation (TSAT) normal range: 20-45%. This shows how much iron is bound to its transporter in your blood. 

B Vitamins: Folate (B9), Cobalamin (B12) and Pyridoxine (B6). B vitamins also help make red blood cells. Lacking B vitamins can cause you to not make enough red blood cells resulting in anemia. (11)

Nutrition Recommendations:

Foods that are high in B12 are meat, poultry, fish, dairy products, and eggs. (12) Fortified breakfast cereal, salmon, russet potatoes, turkey, and avocados are high in B6. (13) Foods high in B9 are legumes and leafy green vegetables. (14)

Foods that are high in iron are meat, poultry, fish, plants, dairy products. (15)

B vitamins and iron supplements may be recommended and may be more common with decreased protein intake. Check out our blog Renal Dietitian’s Guide to Vitamins and Supplements for Chronic Kidney Disease to learn more!

Bone Health – Parathyroid Hormone, Phosphorus, Calcium, Vitamin D

Your kidneys are also interlinked with your bone health and cardiovascular health via your parathyroid hormone (PTH), phosphorus, calcium, and vitamin D levels. 

Your kidneys are responsible for activating vitamin D. Low vitamin D can cause low calcium. When you have low calcium, it stimulates your parathyroid gland to release PTH. 

Your PTH increases phosphorus and calcium absorption in your gut, tells your kidneys not to excrete calcium in your urine, and tells your body to release calcium from your bones. These actions can make your bones weaker and your arteries harder.

The following labs and goals will give you an idea of where you want your levels to stay as healthy as possible. 

Parathyroid-Hormone (PTH) normal range: 10-65. CKD 3 goal is 35-70, CKD 4 goal is 70-110, and CKD 5 goal is 150-300. (16)

Calcium (corrected Ca) normal: 8.5-10.2. 

Vitamin D normal: >20. Ideally >30 and <100. 

Phosphorus normal: 2.7-4.6. 

Nutrition Recommendations:

High amounts of phosphorus in your diet and blood can also activate your parathyroid hormone by decreasing calcium in your blood. Limiting phosphorus in your diet can help control these factors. 

I typically always recommend avoiding phosphate additives in your food when you have kidney disease to help combat this complication. 

Hypertension – Blood Pressure, Sodium, Potassium 

Uncontrolled blood pressure is the second highest cause of kidney disease. (17) Kidney disease can also cause blood pressure problems. Making sure your blood pressure is well controlled is the best way to protect your kidneys from further damage. 

Blood pressure goal: <120-140/80-90. (18, 19)

Your serum sodium level is not typically an indication of how much sodium you are eating. It is a better indication of your hydration level. If you have low sodium, you could be holding onto too much fluid. If you have a high sodium level, you could be dehydrated. 

Sodium goal: <2,300 milligrams (mg) in your daily intake. (20)

Potassium can be tricky because sometimes your kidneys may not be excreting potassium in your urine. This can make it so you need to restrict potassium in your diet. 

But potassium plays an important role in maintaining your blood pressure and lots of foods that are good for you, also tend to be higher in potassium. 

Knowing your potassium level is crucial in being able to find that balance of eating enough potassium to help with blood pressure.

There are several reasons you could have a high blood potassium other than just your food choices though. Uncontrolled blood sugars, metabolic acidosis (low serum CO2), and certain blood pressure medications can affect your potassium levels. (21)

Be sure to discuss these reasons with your nephrologist or renal dietitian. 

Potassium goal: 3.5-5.0.

Nutrition Recommendations:

Know how much sodium, potassium, and fluid you should be getting each day.

I typically recommend anywhere from 1,500 to 2,300 mg of sodium per day depending on your individual needs. Hypertension, fluid retention, and congestive heart failure may affect your recommendations.

Your renal dietitian or nephrologist will be able to give you recommendations for potassium. Knowing your labs will help you determine if you need to adjust your potassium intake but I generally recommend avoiding all potassium additives in your food choices

Diabetes -Blood Sugars, A1C

Uncontrolled diabetes is the second leading cause of kidney disease. Controlling your blood sugars is the best way to preserve your kidney function. Work with your healthcare providers to ensure you are managing your blood sugars to the best of your ability. 

Blood sugar goals: 70-200. (4)

A1C goals: less than 6.5-8.0%. (22)

Nutrition Recommendations:

Blood sugar control is very individualized but typically, you can follow a consistent carbohydrate diet to help stabilize your blood sugars. This just means you’ll be having the same amount of carbohydrates with breakfast, lunch, and dinner. 

You can prevent blood sugar spikes and lows by spreading your carbohydrate intake throughout the day.

If you have Type 1 diabetes, you’ll need to work with your doctor to adjust your insulin doses for better blood sugar management. 

It’s important to note that insulin is broken down in the kidneys so you may need less as your kidney function declines. 

Inflammation – Albumin, Ferritin and Glucose

Albumin, Ferritin and Glucose are common labs that can be assessed to determine inflammation in kidney disease.

Albumin can be low with inflammation. Normal range: 3.4-5.0 g/dL. Ideally, it would be >4.0 g/dL. 

Ferritin can be elevated with inflammation. Normal range: 45-340 ng/dL. 

Glucose (blood sugars) can also be elevated with inflammation and/or infection. Normal range: <120-140 fasting (not eating 2 hours prior), <200 non-fasting. 

Ask your healthcare provider for your specific goals.

Nutrition Recommendations:

There are a lot of contributing factors that could be causing inflammation in your body. 

Your best option for decreasing inflammation is working with a renal dietitian. Controlling blood pressure, diabetes, anemia, bicarbonate levels, and supporting a healthy gut is usually your first line of defense.

Choosing more plant foods can help with your goal of reducing inflammation. (23)

Gout – Uric Acid

Gout and kidney disease can also be interrelated. 

Uric acid is a waste product from purines found naturally in your body and food. It may not be excreted in your urine with kidney disease. (24)

Gout is determined and measured by uric acid levels. High uric acid can cause damage to your kidneys. (24)

Uric Acid Goal: less than 6 mg/dL. (24)

Nutrition Recommendations:

A kidney friendly diet is typically a gout friendly diet. The most important thing with uric acid is to know your levels and discuss them with your doctor.

***Discuss your specific goals with your doctor for all the conditions above.

Relevant Mineral Labs – Magnesium, Zinc, Copper

These minerals may also be affected in kidney disease because of poor filtration of your blood. 

You may need to adjust the food or supplements you are taking to compensate for abnormal blood values.

It is very important to discuss your goals with your doctor or dietitian!

You’re the MVP!

It can be overwhelming trying to make sense of your lab reports.

Use this blog as a guide when you review your labs.

Always discuss your labs with your healthcare team to execute the best plan for protecting your kidneys.

And remember, you are a part of your healthcare team! 

You are your most valuable player (not your doctor or dietitian) when it comes to your kidney disease!

This article was co-written by dietetic student and digital marketing intern Eva McIntosh & reviewed, edited, and co-written by Candace Mooney, MS RDN CSR.

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