Tests to assess kidney function

Kidney function tests that are part of the Comprehensive Metabolic Panel. The International Myeloma Working Group (IMWG) and National Comprehensive Cancer Network (NCCN) both recommend kidney function tests for multiple myeloma patients.

The IMWG Recommendations for the Diagnosis and Management of Myeloma-Related Renal Impairment state that all patients with myeloma at diagnosis and at disease assessment should have:

• serum creatinine
• estimated glomerular filtration rate (eGFR)
• electrolyte measurements 
• free light chain assessment
• urine electrophoresis (UPEP) of a sample from a 24-hour urine collection

Learn about each of these tests and how they are used to diagnose and monitor your disease and kidney function.

The kidneys of a myeloma patient may be damaged by:

• light chain monoclonal proteins
• high blood calcium levels that result from the breakdown of bones 

Serum Creatinine Testing

Creatinine is the waste product from normal muscle breakdown. Impaired kidneys cannot rid the blood of creatinine. As a result, the serum creatinine level rises. Make sure to assess kidney function at diagnosis and at regular intervals thereafter. If you have Bence-Jones (light chain) protein in your urine, ensure your kidney function is regularly evaluated.

Creatinine Clearance Testing

The test for creatinine clearance requires both 24-hour urine collection and a blood sample. Creatinine clearance is the amount of blood per minute that the kidneys can make creatinine-free. While the level of creatinine in the blood goes up with kidney damage, creatinine clearance goes down. 

When is creatinine clearance an issue?
Creatinine clearance of fewer than 40 mL per minute is a "myeloma-defining event (MDE)." An MDE is a sign of early active myeloma in a patient who otherwise does not have CRAB features. These patients should be treated for active myeloma, rather than just observed.

Estimated Glomerular Filtration Rate (eGFR)

The glomeruli are the basic filtration system of the kidneys. The IMWG diagnostic criteria use estimated glomerular filtration rate (eGFR) to determine the "R" for renal in the CRAB criteria. eGFR is more reliable measurement than serum creatinine. Creatinine clearance tests automatically calculate eGFR. 

The eGFR is expressed as an estimation of how many milliliters of creatinine are cleared per minute per square meter of your body mass. One issue is that this test is not always accurate for people who are older than 70, very overweight, very muscular, or pregnant.

Electrolytes

Electrolytes are substances that conduct electricity in the body. Examples of electrolytes include sodium, potassium, chloride, and bicarbonate. Electrolytes do the following:

• regulate nerve function
• regulate muscle function
• hydrate the body
• balance blood acidity and pressure
• rebuild damaged tissue

Your healthcare professional will evaluate your electrolyte levels to see if they are off. Electrolyte imbalances may cause kidney disease.

Blood urea nitrogen, or BUN

Blood urea nitrogen (BUN) is a measurement of a waste product that accumulates in the blood. When the body breaks down proteins, the amount of blood urea nitrogen increases. This increase indicates damage to the kidneys or liver. 

See the section on tests that assess monoclonal protein for more about

• serum free light chain assay
• urine protein electrophoresis

What's Next?