Reference Methods for the Total Bilirubin

Bilirubin, which gives red blood cells their color, can be measured by a skin test or a blood test. You may need to have your bilirubin tested if you experience jaundice or your doctor suspects liver problems or liver disease. Your doctor may also test bilirubin levels to check on any medication you're taking and its effect on the liver.

What Is Bilirubin?

• Bilirubin is a product of the blood. It's a dark yellowish color and found in the hemoglobin of red blood cells, helping to give them their color. Bilirubin can be found in bile and urine as old red blood cells break down and new blood cells are formed. It lends the color to urine and fecal matter as bilirubin is removed from the body.

Why Test for Bilirubin?

• The liver cleans out the blood and any bilirubin found in it. If your doctor suspects liver problems, a bilirubin measurement can help see if the liver is able to keep up with cleaning out the blood and bilirubin. High levels could mean the liver isn't removing the bilirubin properly, or could signal a medical problem with excessive breakdown of red blood cells. Jaundice is caused by such an excess of bilirubin that it makes its way into the skin and eyes, causing the telltale yellow coloring.

Skin Testing

• Skin testing of bilirubin levels is done by measuring the optical density of the skin with certain wavelengths. However, the measurement needs a comparison factor, so skin testing of bilirubin levels isn't very accurate or necessarily reliable, so should be used only as a screening tool. Also, skin testing needs to be performed several times so an average of the results can be used to determine the bilirubin level.

Blood Testing

• There are several ways to test the blood for bilirubin levels depending on the photometric device or chemical reagent used to detect it. Blood gas can be checked by ultrasonic methods without the use of a chemical reagent, or a chemical reagent may be used that binds to the bilirubin. The Powell method uses a diazo reagent with sodium benzoate-urea solution. The Jendrassik and Gróf method uses caffeine combined with sodium acetate, sodium benzoate and a diazo reagent. The King and Coxon method uses ammonium sulphamate, sodium azide and ethanol with a diazo reagent.

Methods Vary on Results

• All the methods to detect bilirubin levels vary and can give inaccurate results that are too high or too low. Currently, there's no one precise and completely accurate method to determine the exact level of bilirubin in the blood. All testing gives an estimated amount and is adequate to determine liver function or problems with the liver removing bilirubin from the blood.