Side Effect: Kidney function blood tests (BUN and SCr)

What are Kidney function blood tests (BUN and SCr)?

Kidney function blood tests (BUN and SCr) are commonly used to evaluate the health of the kidneys by measuring the levels of certain substances in the blood. Two of the most commonly measured kidney function tests are:

• blood urea nitrogen, also known as the B.U.N.
  • Normal range: less than 24 mg/dL
    
    
• serum creatinine (SCr)
  • Normal range: less than 1.3 mg/dL

BUN is a waste product that is produced when the liver breaks down proteins, and and releases nitrogen. The nitrogen then combines with hydrogen, carbon, and oxygen to form urea, which is a waste product that is removed from the blood by the kidneys.

SCr is a waste product that is produced by muscle metabolism when creatinine is released into the serum (the bloodstream), and just like the BUN, creatinine is also removed from the blood by the kidneys.

What do Kidney function blood tests (BUN and SCr) look like?

Although you cannot look at someone and see if their kidneys are working, an elevated BUN or SCr levels can indicate that the kidneys are not functioning properly. Thankfully, both of these tests can be performed together in either a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP) blood test, which are routine screening tests that measures a variety of different substances in the blood.

• Your doctor may also order a test to see how much protein is in your urine depending on the treatment that you are receiving.

Kidney function blood tests are important because they can help identify kidney problems early on when treatment is more effective. They can also be used to monitor for progression of kidney disease and evaluate the effectiveness of treatment.

Who needs Kidney function blood tests (BUN and SCr) measured?

All patients being treated for cancer should have regular kidney function tests. Abnormal kidney function occurs frequently in patients receiving treatment for cancer. This can result in chemotherapy dose reductions or delays in treatment. Patients on the following treatments are at an increased risk:

• Chemotherapy – cisplatin, carboplatin, ifosfamide, methotrexate
• Vascular endothelial growth factor (VEGF) inhibitors – bevacizumab, ramucirumab, aflibercept
• Tyrosine kinase inhibitors (TKIs) - imatinib, bosutinib, sorafenib, and sunitinib, crizotinib, gefitinib, pazopanib, lenvatinib, and vandetanib
• poly-ADP ribose polymerase (PARP) inhibitors - olaparib and rucaparib
• Bruton tyrosine kinase (BTK) inhibitors – ibrutinib and pirtobrutinib

The SCr can be falsely elevated by eating a lot of protein, since protein is converted to muscle and subsequently broken down into creatinine. If you are eating high-protein shakes or smoothies, tell your doctor so that they can interpret the results of the SCr test appropriately.

Additional causes of an increase in the BUN or SCr include:

• Dehydration, resulting from vomiting, diarrhea or not drinking enough fluids
• Urinary tract obstruction (example: from a kidney stone)
• Congestive heart failure or swelling in the extremities causing less fluid to be filtered by the kidneys
• Gastrointestinal bleeding
• Certain medications, such as cyclosporine or overuse of certain diuretics

How do you prevent Kidney function blood tests (BUN and SCr) from getting worse?

Staying well-hydrated before and during chemotherapy can help protect the kidneys from damage. Oral hydration is helpful, but your physician may also order intravenous (IV) fluids to help maintain kidney function and flush out toxins. Some medications can protect the kidneys during cancer treatment, and these may be administered before specific therapies. It is important to catch any signs of kidney dysfunction early to prevent irreversible kidney damage.

How do you treat Kidney function blood tests (BUN and SCr) when they are elevated?

Treatment for kidney dysfunction depends on the underlying cause and severity of the condition. In some cases, simply reducing the dose of chemotherapy or switching to a different medication may be sufficient to improve kidney function. In more severe cases, dialysis may be necessary.