Kidney function tests that are part of the Comprehensive Metabolic Panel are recommended for multiple myeloma patients by both the International Myeloma Working Group (IMWG) and National Comprehensive Cancer Network (NCCN). 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), and electrolyte measurements as well as free light chain assessment and 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 or by high blood calcium levels that result from the breakdown of bones.
Serum Creatinine Testing
Creatinine is the waste product from normal muscle breakdown. When the kidneys are impaired, they cannot rid the blood of creatinine, so the serum creatinine level rises. It is very important to assess kidney function at diagnosis and at regular intervals thereafter, particularly if you have Bence-Jones (light chain) protein in your urine.
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. Remember that while the level of creatinine in the blood increases with kidney damage, creatinine clearance is decreased. Creatinine clearance of less than 40 mL per minute is considered a "myeloma-defining event (MDE)," that 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 to determine the "R" for renal in the CRAB criteria, rather than serum creatinine, because it is a more reliable measurement. The eGFR is calculated automatically as part of the creatinine clearance test. 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 caveat is that this test is not accurate for people who are older than 70, very overweight, very muscular, or pregnant.
Electrolytes include sodium, potassium, chloride, and bicarbonate. These are substances that conduct electricity in the body. Electrolytes regulate nerve and muscle function, hydrate the body, balance blood acidity and pressure, and help rebuild damaged tissue. Electrolyte concentrations are evaluated to investigate conditions that cause electrolyte imbalances, including 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, indicating if the kidneys or liver are damaged. For information on the serum free light chain assay and urine protein electrophoresis, see the section on tests that assess monoclonal protein.