Serum total bilirubin measurement is used to evaluate liver function, to evaluate a wide range of diseases affecting the production, uptake, storage, metabolism or excretion of bilirubin, and to monitor the efficacy of phototherapy in newborns.
Bilirubin, one of the components of bile, is formed in the liver, spleen, and bone marrow. It is also formed as a result of the breakdown of hemoglobin as occurs during the destruction of red blood cells. There are three types of bilirubin: total, direct (conjugated) and indirect (unconjugated). Total bilirubin is made up of the sum of direct bilirubin plus indirect bilirubin. The level of total bilirubin is increased in any type of jaundice.
Normally, direct or conjugated bilirubin is secreted from the gastrointestinal tract, with only a small amount entering the bloodstream. It was originally called "immediate" because this water-soluble bilirubin reacts directly with the reagent added to the samples. Its value increases in the blood during the obstructive jaundice (from stones to bile) and appears as jaundice as bilirubin cannot reach the intestine to be excreted and instead enters the bloodstream where it is excreted by the kidneys. Instant bilirubin is the only type of bilirubin that can penetrate the renal coil and so is the only type of bilirubin that can be found in the urine.
Indirect bilirubin, also known as free or unbound bilirubin, is usually found in the bloodstream. Its name derives from the fact that this water-insoluble bilirubin does not react directly with the reagents added to the samples. Alcohol must be added to make a reaction. Indirect bilirubin is increased in cases of hemolytic jaundice, in which the degradation of hemoglobin results in higher levels of indirect bilirubin. This is the type of bilirubin that increases in cases of hepatocellular dysfunction such as hepatitis.
Usually, only total bilirubin is measured. If total bilirubin measurement is not possible, further testing is carried out to determine the level of direct and indirect bilirubin.
Possible Interpretations of Pathological Values
- Medications that can increase total bilirubin: Allopurinol, anabolic steroids, anthelmintics, ascorbic acid, azathioprine, chloropropamide, cholinergic, codeine, dextran, mefeneprolein, diuretic, epinephrine, epinephrine oral contraceptives, phenazopyridine, phenothiazines, quinidine, rifampicin, streptomycin, theophylline, tyrosine, vitamin A.
- Medications that can reduce total bilirubin: Barbiturates, caffeine, chloride, citrates, corticosteroids, ethanol, penicillin, proteins, salicylates, sulfonamides, urea.
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. Correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.