Confirming Bilirubin Results: A SelectScience Interview

Ictotest® Reagent Tablets are used to test for the presence of bilirubin in urine. The presence of bilirubin is an important finding in the evaluation of liver function and positive detection could be an indication of liver disease such as jaundice, cirrhosis or hepatitis. Hospitals and clinical laboratories rely on Siemens’ Ictotest reagent tablets to confirm bilirubin results, prior to providing the results to their customers.

Dr. Saeed A. Jortani tells our Clinical Editor, Sonia Nicholas, more about this important test. Dr. Jortani is the Associate Professor of Pathology and Laboratory Medicine, at the University of Louisville, School of Medicine, and Associate Director of University of Louisville’s Clinical Chemistry and Toxicology Laboratory.

Dr. Jortani, could you tell us why it is important to test for bilirubin in the urine?

Bilirubin is formed by the breakdown of hemoglobin in the reticuloendothelial cells of the spleen and bone marrow. It is linked to albumin in the bloodstream and transported to the liver. This albumin-bound form, which is also known as indirect bilirubin, is insoluble in water and does not appear in the urine. In the liver cells however, it is separated from the albumin and conjugated with glucuronic acid to form water-soluble conjugated bilirubin, also known as direct bilirubin. The liver cells that form the conjugated bilirubin excrete it into the bile, where it is then excreted into the intestinal tract through the bile duct. Bilirubin in the urine indicates the presence of hepatocellular disease or intra- or extra-hepatic biliary obstruction. More simply, it is an early sign of liver disorders and therefore a useful diagnostic tool.

How often do false positive results occur with front-line tests such as the urine-strip? What causes false-positive results?

We are planning studies to assess this rate of false positive bilirubin. Drugs such as Etodolac, Acethexamide, and Chlorpromazine have been shown to cause false positive results.

What is the potential impact on the patient if a false-positive result is not detected?

If a positive bilirubin result occurs, a physician will typically move to another round of diagnostic testing to gather a more specified picture of the patient’s health. In the event of a false-positive, none of that additional testing would be warranted. These additional tests cost time and money for both the physician and the patient, and in some cases the additional testing can be more invasive (e.g. a blood test).

How do you rule out these false-positive results?

In the event that you obtain a positive bilirubin result using a urine chemistry dipstick, for example – you can additionally test the same urine sample using a confirmatory product such as Ictotest® reagent tablets which is based on the diazotization reaction, and has been used by physicians for more than 60 years. You can also obtain a blood sample to obtain a fully quantitative result via a laboratory method. Obtaining a positive urine chemistry result, but a negative bilirubin result with Ictotest® or a lab method, would indicate a false positive.

How does the Ictotest work?

Ictotest is based on the diazotization reaction, whereby the coupling of a unique solid diazonium salt with bilirubin in an acid medium presents a blue or purple reaction. In terms of performing the test, you place 10 drops of urine onto the absorbent mat, this is provided with Ictotest, shake one Ictotest Reagent Tablet into the bottle cap and transfer the tablet to the center of the moistened mat. Place one drop of distilled water onto the tablet. Wait 5 seconds, and then place a second drop of distilled water onto the tablet so that the distilled water runs off the tablet onto the mat. You then observe the color of the mat around and under the tablet at 60 seconds. The presence of a blue or purple color on the mat indicates that bilirubin is present.

Find out more about Siemens Ictotest Reagent Tablets

Dr. Saeed A. Jortani, Associate Professor of Pathology and Laboratory Medicine, at the University of Louisville, School of Medicine, and Associate Director of University of Louisville’s Clinical Chemistry and Toxicology Laboratory.