Know Your Numbers

Know Your Numbers: Understanding Kidney Blood and Urine Tests

Your kidneys are the unsung heroes of your body’s filtration system. They work around the clock to remove waste, balance fluids, and regulate essential minerals like sodium, potassium, calcium, and phosphorus. Despite their vital role, kidney disease often develops silently—without noticeable symptoms in the early stages.

That’s why regular kidney function tests are essential. They offer early warning signs, track how well your kidneys are working, and help guide treatment decisions. At Renal Specialists of Houston, we’re dedicated to educating you on what these tests mean so you can feel informed, empowered, and involved in your care.

What Are Kidney Function Tests?

Kidney function tests are a group of blood and urine tests that help us understand how well your kidneys are working. They help with:

• Detecting early signs of kidney damage – when it’s most treatable • Monitoring progression of kidney disease and evaluating how well your treatment plan is working
• Adjusting medications and diet
• Evaluating conditions like high blood pressure or diabetes that affect kidney health
• Preventing complications like bone disease, anemia, or high potassium

Types of Kidney Function Tests

Here are the most common tests used to assess kidney health:

1. Blood Urea Nitrogen (BUN)

• What it is: Measures the amount of urea nitrogen, a waste product from protein breakdown.
• Why it matters: High BUN may mean your kidneys aren’t clearing waste effectively, but there may be other causes as well.

2. Serum Creatinine

• What it is: Creatinine is a waste product from muscles.
• Why it matters: Elevated creatinine can signal reduced kidney function.

3. Glomerular Filtration Rate (GFR)

• What it is: Estimates how much blood your kidneys filter each minute.
• Why it matters: A low GFR indicates declining kidney function. This is one of the most important markers of kidney health.

4. Urinalysis

• What it is: Analyzes urine for protein, sugar, blood, or signs of infection.
• Why it matters: Abnormal results may signal kidney damage or urinary tract issues.

5. Urine Albumin-to-Creatinine Ratio (UACR)

• What it is: Compares levels of protein (albumin) to creatinine in the urine.
• Why it matters: An early indicator of kidney damage—especially in diabetes and high blood pressure. The higher the ratio, the more we are concerned.

Understanding Additional Key Labs in Kidney Disease

These lab results provide a deeper look into how your kidneys regulate your body’s internal balance:

Sodium (Na⁺)

• Role: Maintains fluid balance and supports nerves and muscles.
• Why it matters: Abnormal levels may cause swelling, confusion, or blood pressure changes. It is not, however, a measure of whether you are eating the right amount of salt.

Potassium (K⁺)

• Role: Essential for heart rhythm and muscle function.
• Why it matters: Too much potassium (hyperkalemia) can lead to dangerous heart problems if not properly managed.

Total CO₂ (Bicarbonate)

• Role: Helps maintain the body’s acid-base balance.
• Why it matters: Low bicarbonate may mean the body is too acidic, which can lead to muscle loss or bone weakness. There is also evidence that it may speed up kidney damage

Calcium (Ca²⁺)

• Role: Vital for bones, muscles, and nerves.
• Why it matters: Kidney disease can disturb calcium levels, increasing risk for bone problems or heart issues.

Phosphorus (PO₄³⁻)

• Role: Works with calcium to build bones.
• Why it matters: High phosphorus can cause itching and damages bones and blood vessels – increasing the risk of heart disease. The kidneys usually keep phosphorus levels in check.

Parathyroid Hormone (PTH)

• Role: Regulates calcium and phosphorus levels.
• Why it matters: As kidney function declines, PTH may rise, contributing to bone pain and weakening (renal osteodystrophy).

Hemoglobin (Hgb) & Hematocrit (Hct)

• Role: Both measure red blood cells, which carry oxygen throughout your body.
• Why it matters: Low levels indicate anemia, common in kidney disease, and can cause fatigue, weakness, or shortness of breath.

When Should You Get Tested?

You should have regular kidney function tests if you:

• Have high blood pressure or diabetes
• Have a family history of kidney disease
• Are over age 60
• Experience symptoms like swelling, fatigue, or changes in urination • Take medications that may affect the kidneys

Baseline testing is recommended for anyone! If you're at higher risk, annual follow-up tests are typically advised.

Interpreting Your Results

Your Renal Specialists of Houston healthcare provider will walk you through what each result means. Elevated creatinine or BUN, an abnormal GFR, or protein in your urine may be signs of kidney disease—but results always need to be considered as part of the bigger picture.
Let’s work together to protect your kidneys – one test at a time!