The kidneys are responsible for filtering waste products and excess water from the body. Kidney function can be assessed via a series of blood and urine tests that show how efficiently the kidneys are operating. Kidney blood tests include blood urea levels and glomerular filtration rate.
About the Kidneys and Kidney Diseases
The kidneys are a pair of fist-sized organs located on the back side of the torso, just below the level of the rib cage. These organs filter the blood to remove excess water and waste products. The waste and water is then excreted as urine.
Within the kidney are hundreds of thousands of tiny units called nephrons. Each nephron contains a glomerulus and a urine-collecting tube. The glomerulus is a tiny blood-filtering capillary which removes waste from blood, and then diverts the waste into the urine-collecting tubule.
Certain diseases can reduce kidney function, primarily by damaging the nephrons. Diabetes, high blood pressure, and other glomerular diseases can damage glomeruli in the nephrons, and reduce the filtering capabilities of the kidneys. Medications, poisons, kidney trauma, and certain congenital or hereditary diseases can also cause kidney damage that results in reduced kidney function.
Diagnostic Kidney Blood Tests
When an individual first presents with kidney problems, a series of blood and urine tests can help diagnose the problem.
In addition, these initial kidney blood tests are used to develop a baseline for kidney function at the time the individual undergoes the tests. Over time, as new tests are carried out, these can be compared to previous tests to determine whether kidney function is improving or becoming worse. These tests are therefore useful for monitoring a patient's condition, and evaluating the progression of kidney disease.
In addition these tests can help monitor the efficacy of kidney disease treatments.
Comprehensive Metabolic Panel
A comprehensive metabolic panel provides information not only about kidney function, but also liver function, electrolyte and mineral balance, blood sugar, blood protein levels, and acid/base balance.
There are fourteen tests in a comprehensive metabolic panel, measuring values of the following:
Electrolytes: sodium, potassium, carbon dioxide, chloride
Kidney function: blood urea nitrogen, creatinine
Liver function: alkaline phosphatase, alanine amino transferase, aspartate amino transferase, bilirubin
Blood Urea Nitrogen
Urea is a form of nitrogenous waste product released by cells as they metabolize protein. When kidneys are healthy, the filter urea out of the blood and excrete it in urine. Diseased kidneys cannot filter urea effectively, so this waste product remains in the blood.
A normal blood urea value is 7 to 20 milligrams of urea per 100mls of blood. If blood urea levels increase above this level it can indicate kidney problems. In addition, a high blood urea value can be an indicator of heart failure or dehydration.
The eGFR value is the glomerular filtration rate. This measures how well the kidneys filter waste products from the blood. The calculation is made by measuring levels of a protein called creatinine in the blood.
The eGFR is the best indicator of kidney function, because eGFR levels closely correlate with stages of chronic kidney disease.
- An eGFR of 90 or more is considered a normal reading.
- An eGFR of 60 or less for three months or longer is considered a marker of chronic kidney disease.
- When eGFR is between 30 and 59, the body’s hormone and mineral levels can become imbalanced; medication, supplements, or dietary changes might be needed.
- An eGRF of 15 to 29 is a severe reduction compared to the normal value. At this point a patient is likely to require regular dialysis treatments.
- When the eGFR drops below 15, dialysis is a definite requirement; a patient with this eGFR reading is a kidney transplant candidate if he or she meets other criteria.
The results of the eGFR can also be used in conjunction with a urine test for creatinine, called a GFR. This is carried out so that blood and urine levels of creatinine can be compared.