Know Your Numbers: Understanding Key Lab Tests For Patients with Kidney Disease

These tests help measure how well your kidneys filter waste from your blood.

Creatinine is a waste product made by your muscles from the breakdown of a compound called creatine. Because the kidneys are responsible for removing creatinine from your body, monitoring the amount of creatinine in your blood is a key way to check on the health of your kidneys.

Estimated Glomerular Filtration Rate (eGFR) estimates how well your kidneys are filtering waste, toxins, and extra fluid from your body every minute.  The eGFR is also useful to help detect kidney disease, track progression of the kidney disease, and also help guide treatment decisions.

The eGFR calculation is based on your blood creatinine level, age, sex, and sometimes race. It calculates how much blood is passing through the glomeruli (tiny filtering units in your kidneys) each minute.

The eGFR level is used to help determine how severe your kidney damage is from Stage 1 (mild) chronic kidney disease (CKD) to Stage 5 (end stage kidney failure).

Urine Albumin-to-Creatine Ratio (uACR) is a tool to check for kidney damage. The presence of albumin (a protein found in the blood) in the urine (called albuminuria or proteinuria) is one of the earliest signs your kidneys are leaking protein, which is a sign of kidney disease.

The uACR test counts the amount of albumin in your urine compared to creatinine (a waste product, mentioned above). The result of your uACR is used together with your eGFR to determine the stage of kidney disease and the risk of your kidney disease progressing.

A high uACR is often linked with a higher risk of kidney failure, heart disease, and death.

Blood Urea Nitrogen (BUN) is a common blood test that measures how much urea nitrogen is in your blood. When your body breaks down protein from food, it creates urea. Urea is a waste product. Urea travels through your blood to your kidneys and the kidneys will normally filter it out into your urine.

If you have kidney disease, urea builds up in your blood and causes a high BUN level. That is why the BUN value is another key marker when you have kidney disease as it helps assess how well your kidneys are removing waste products from your body.

BUN may also rise in the setting of dehydration, bleeding, high protein intake, or heart failure.

Along with your creatinine and your eGFR, your BUN is used to evaluate and track your CKD.

Key Questions to Ask Your Doctor

• What does my Creatine/eGFR/uACR/BUN level mean for my stage of kidney disease?
• Is my kidney function stable, improving, or declining?
• What factors could cause my kidney function numbers to change?

These are minerals in the body that carry an electric charge and help control important functions like nerve and muscle activity, hydration, and maintaining the body’s PH balance. 

Potassium (K) is a mineral and electrolyte important in regulating your heart rhythm and in supporting muscle and nerve function. Your kidneys are responsible for filtering out excess potassium from your blood through the urine. If your kidneys cannot filter potassium, potassium will build up in the bloodstream. A high potassium level, also known as hyperkalemia, is life threatening because it may cause cardiac arrest. Learn more about potassium at areyouok.organd mark your calendar for National High Potassium Awareness Day (May 1st).

Sodium (Na) is an electrolyte and mineral closely monitored to assess your fluid and blood pressure. When you have kidney disease, your kidneys may not be able to get rid of excess sodium. Excess sodium, also called hypernatremia, may lead to fluid retention, swelling (edema), high blood pressure (hypertension), and even congestive heart failure.

Calcium (Ca) is an electrolyte and very important mineral in keeping bones and teeth strong and healthy. Calcium balance can be disrupted in kidney disease leading to serious complications which is why your calcium must be monitored closely in kidney disease. A high level of calcium in the blood is called hypercalcemia which can lead to various symptoms and complications such as bone weakening, kidney stones, and heart and brain dysfunction.

Key Questions to Ask Your Doctor

• Are any of my electrolytes too high or too low?
• Do I need to change my diet based on these numbers?
• Could any of my medications affect these levels?

Bone & Mineral Health refers to how the body regulates minerals like calcium and phosphorus to keep bones strong and maintain healthy blood levels.

Phosphorus (P) is another important electrolyte and mineral that is essential for bone formation, energy metabolism, and cell function.  About 85% of phosphorus is stored in bones. 

The kidneys are primarily responsible for helping maintain a balanced level by removing excess phosphorus. When the kidneys are not properly functioning, phosphorus can build up, causing hyperphosphatemia, and can bind with calcium pulling calcium out of the bone - this causes those calcium deposits (vascular calcification) and weak bones. Learn more about phosphorus at
www.thehiddenpinkidneydisease.org and mark your calendar for National Phosphorus Awareness Day (April 5th).

Vitamin D is a fat-soluble vitamin essential for bone health, immune function, and maintaining a balance between your calcium and phosphorus levels. 

Vitamin D is inactive when first consumed and healthy kidneys activate that inactive vitamin D to an active form called calcitriol. This activation is a necessary step in helping your body absorb calcium from food.

When kidneys are not functioning properly, they cannot convert Vitamin D into calcitriol so less calcium is absorbed from the intestines. Reduced calcium absorption may lead to low levels of calcium.

Because Vitamin D is needed for calcium absorption, if the kidneys are not fully working, Vitamin D will remain inactive, leading to: 1) low calcium 2) bone loss 3) overactive parathyroid glands (known as secondary hyperparathyroidism), and 4) higher risk of fractures.

Parathyroid Hormone (PTH) is a hormone produced by the parathyroid glands, small endocrine glands (specialized organs that produce and secrete hormones) located behind your thyroid gland, to regulate the level of calcium in your blood.

Key Questions to Ask Your Doctor

• Are my PTH and vitamin D levels in a healthy range?
• Do I need supplements or medications to manage bone health?
• How do these numbers affect my risk for bone disease?

If the calcium level drops in your blood, the parathyroid glands will release PTH.

Anemia happens when you do not have enough healthy red blood cells or hemoglobin to carry oxygen throughout the body.

Erythropoietin (EPO) is a hormone produced by the kidneys and is released when the kidneys sense low oxygen levels in your blood. The hormone will tell your bone marrow to make red blood cells. When the kidneys are damaged, they may not produce enough EPO, so fewer RBCs are made, resulting in anemia. 

Hemoglobin (Hb) is a protein in red blood cells (RBCs) that transports oxygen from your lungs to the rest of your body. If you do not have enough hemoglobin, your organs, muscles and tissues will not get enough oxygen, leading to anemia.

If the hemoglobin drops too low, you may be at risk of heart failure because severe anemia makes your heart work harder.

Key Questions to Ask Your Doctor

• Am I showing signs of anemia related to kidney disease?
• Do I need iron, Erythropoiesis-Stimulating Agent (ESA) injections, or other oral anemia treatments?
• How often should these labs be monitored?

Iron Studies – especially Ferritin and Transferrin Saturation (TSAT) – are key lab tests used to understand iron levels and anemia. These tests help doctors determine whether your body has enough iron to make red blood cells. Your healthcare provider may also screen your B12 and folate (vitamin B9) levels, as low levels of these may also lower hemoglobin. 

Key Questions to Ask Your Doctor

• What are my ferritin and TSAT levels?
• Are my iron levels low, normal, or high?
• Do my numbers suggest iron deficiency or inflammation?
• Would iron supplements or IV iron help my anemia?
• How often should my iron studies be checked?

Tracking blood sugar levels over time can help manage diabetes and reduce the risk of complications, including kidney damage.

Hemoglobin A1c (HbA1c) measures your average blood sugar level over the past 2-3 months and reflects how much glucose (sugar) has been attached to your red blood cells.

HbA1c is an important tool to screen for diabetes. For persons with diabetes, it is also an important marker to evaluate how well diabetes is being managed. Because diabetes is the leading cause of CKD, the HbA1c is especially important since uncontrolled blood sugar contributes to worsening kidney disease by damaging the blood vessels in the kidneys. Over time this leads to protein in the urine, progression of kidney disease, and even kidney failure.

Key Questions to Ask Your Doctor

• What is my A1C level, and what does it mean?
• Are my fasting glucose levels normal?
• Am I at risk for prediabetes or diabetes?
• How often should I be screened for diabetes?
• What lifestyle changes could help lower my blood sugar risk?

A urine test is another tool used when screening for kidney disease. It may show early signs of kidney disease, even before blood tests or before any physical symptoms appear.

Urinalysis screens for protein in the urine (proteinuria), blood in the urine (hematuria), and other abnormalities, such as glucose (sugar) in the urine. 

This test will also screen for white blood cells and nitrites – two signs that can indicate a urinary tract infection (UTI), which can worsen your kidney function if left untreated.

Albumin is a protein made by the liver and works to keep fluid in your blood. If your body does not have enough albumin, fluid will leak into the tissues and cause swelling. Healthy kidneys help keep albumin in your blood where it belongs.

When kidneys are not properly functioning, albumin can leak into the urine, which is called albuminuria. High levels of albumin in urine is an early sign of kidney damage, which often appear before other symptoms. Low levels of albumin may suggest you are losing protein in your urine and may also indicate malnutrition.

The albumin level provides key information about your kidney function, nutritional status, and overall health and will be monitored to help track the progression of CKD.

Key Questions to Ask Your Doctor

• Do I have protein in my urine?
• Is the amount increasing or decreasing?
• What treatments can help reduce protein loss?

Fluid and Acid-Base Balance refers to how the body regulates water levels and blood pH to keep organs functioning properly. 

Bicarbonate (HCO3-) is an electrolyte and an alkaline substance (a substance that dissolves in water) that helps counteract excess acid in your blood. Healthy kidneys reabsorb bicarbonate and help to keep your blood pH (measure of the acidity or alkalinity of blood) stable. 

In CKD, kidneys are not able to perform this function, leading to metabolic acidosis, or too much acid in the blood. Metabolic acidosis can worsen kidney damage.Your bicarbonate level helps determine whether you will need to take oral sodium bicarbonate tablets or adjust your diet to help neutralize your blood. 

Key Questions to Ask Your Doctor

• Are my labs showing signs of fluid imbalance?
• Do I have metabolic acidosis?
• Should I change my fluid intake or diet?
• Are any medications needed to help balance my electrolytes or pH?
• How often should these labs be monitored?