What does an increase in the indirect fraction mean?
Bilirubin is formed during the breakdown of hemoglobin and first circulates in the blood in an unbound form - this is the indirect fraction. In the liver, it combines with glucuronic acid, becomes direct, water-soluble, and is excreted in bile. Determining factions answers the question at what stage the failure occurred.
An isolated increase in indirect bilirubin with normal transaminases indicates either increased breakdown of red blood cells or a violation of the uptake and binding of bilirubin in the liver. The first option is hemolysis in autoimmune, hereditary anemia, after transfusions and in some infections; it is accompanied by a decrease in hemoglobin and an increase in reticulocytes and LDH.
The second and most common variant is Gilbert's syndrome, an inherited condition in which the activity of the enzyme that binds bilirubin is reduced. It occurs in several percent of the population, manifests itself as mild jaundice of the sclera due to fasting, stress, infection or physical activity and is not a disease in the full sense of the word: the liver is healthy, the prognosis is favorable, and no treatment is required. A separate and important area is neonatal jaundice, where it is the level of indirect bilirubin that determines the need for phototherapy, since this fraction is able to penetrate the brain.
How to read reference values
Each form contains a reference interval - a range of values typical for healthy people. It depends on the methodology and equipment of a particular laboratory, so it is incorrect to directly compare the results of different laboratories; To monitor over time, it is better to take tests in one place.
The reference interval covers most healthy people, but not all: a slight deviation may be an individual norm. Conversely, a value within the interval is sometimes a deviation for a particular person if he previously had different numbers.
What distorts the result
The most common causes of errors are not related to the laboratory, but to preparation. Eating changes the levels of glucose, lipids and a number of enzymes. Physical activity the day before increases creatine kinase and transaminases. Stress affects hormones and glucose.
The sampling technique is also important: prolonged application of a tourniquet increases potassium and protein fractions, and hemolysis of the sample makes several indicators unreliable. If the result is questionable, it is better to retake the test rather than start treatment immediately.
Express methods and their place
Express tests provide an answer in minutes and are indispensable where speed is important: upon admission to a hospital, before emergency surgery, when examining contact persons. Their sensitivity is lower than laboratory methods, so a positive result always requires confirmation.
A negative rapid test early after possible infection also does not exclude infection: during the serological window, antigens and antibodies have not yet reached detectable levels.