I'm very tired right now but will do my best to shed some light. Hopefully someone else will come along and make everything very clear.
Bilirubin tested in the laboratory can be tested as "total bilirubin", "direct bilirubin" or "indirect bilirubin". Direct bilirubin is also conjugated bilirubin and indirect is also called unconjugated bilirubin or free blilrubin. Total bilirubin is a combination of both direct (conjugated) and indirect (unconjugated) bilirubin. Unconjugated bilirubin is also called "free" because it is floating around free in the blood whereas the conjugated bilirubin is not free... it's bound to albumin as it travels to the liver and then intestines and then excreted in the stool.
Most (75-85%) bilirubin is produced by the breakdown of RBCs (the heme part of hemeglobin). The heme portion is affected by an enzyme that changes heme into biliverdin and then another enzyme changes the biliverdin into bilirubin. This occurs in the reticuloendothelial system. Bilirubin at this point is is unconjugated (in its indirect-reacting form) and is then released into the plasma.
Bilirubin is not very soluble so it prefers to bind tightly to albumin which acts as its carrier protein. The ability of the bilirubin to bind to albumin can be affected by many things like sick, very low birth weight preemies, the plasma pH level, how much free fatty acids are in the plasma and certain drugs.
This unconjugated (indirect) bilirubin riding on the albumin makes its way to the liver where it becomes conjugated by two other enzymes and some glucuronic acid made from glucose. So, the interaction of unconjugated (indirect/free) bilirubin with these liver enzymes & glucuronic acid is what turns the unconjugated bilirubin into conjugated (direct) bilirubin.
Once the bilirubin is conjugated (direct), it is excreted through the bowel. The bowel however has another enzyme which can convert conjugated (direct) bilirubin back into unconjugated (indirect) bilirubin and the glucuronic acid and then be reabsorbed back into the blood stream.
The unconjugated (indirect) bilirubin is what is toxic to the body and can cause kernicterus (a build up of unconjugated bilirubin in the brain) which can lead to neurological problems like cerebral palsy, mental retardation, vision and hearing problems and some scientists believe that mild learning disabilities can result from high levels of unconjugated bilirubin). With high levels the doctors will perform an exchange transfusion of blood for the baby which usually corrects the problem.
An exchange transfusion can be done for serve anemia, removal of antibody-coated red blood cells in hemolytic disease (blood incompatibility of baby and mother), or removal of excess unconjugated bilirubin regardless of the cause. Excess unconjugated bilirubin can be caused by certain enzyme disorders, polycythemia, etc.
The heme portion of bilirubin is what causes the skin and eye sclera to have a yellowish cast and makes the stools have a greenish appearance.
In the instance of a newborn baby... Their blood type and Rh factor is checked right after birth and compared with their mother's to see if there is a possible blood incompatibility. If there is, the doctor usually orders a "Total and Direct Bilirubin" (from the baby's blood serum) to find out how much total bilirubin is in the body and just how much of it is the dreaded direct (unconjugated) type, because these babies can get jaundiced fast and severely. Lots of term babies and most preterm babies become jaundiced during their first few days of life simply because their red blood cells are different and their body systems are immature. When one of these babies who did not have a blood incompatibility at birth starts to look jaundiced the doctor often orders either a "Total (Serum) Bilirubin" or a "Total and Direct Bilirubin" to have as a baseline. They order the Total and Direct more often on preemies since they tend to have more problems in that area than term babies do. Regardless, they will decide, depending on the baby's age and bilirubin levels whether to begin phototherapy or check the bilirubin again in a few hours. The babies with blood incompatibilities often are jaundiced before they are 24 hours old... sometimes even within an hour or two. The other babies jaundice usually occurs after they are 24 hours old and seems to peak around the third to fifth day for normal term babies.
The lab results might look like this:
"Total & Direct Bilirubin" (or) "Fractionated Bilirubin" (meaning broken down into its separate parts).
Total Bilirubin............ 9.3 mg/dl
Direct Bilirubin........... 7.5 mg/dl
Indirect Bilirubin......... 1.8 mg/dl
So, to answer your question, a "Total Serum Bilirubin" is the same as a "Total Bilirubin". "Conjugated Bilirubin" is the same as "Direct Bilirubin" and is simply a broken down part of the total bilirubin amount. The way I remember these terms is that the Con
ly to poop-jail
(and jail is the poop in the diaper). Conjugated (direct) bilirubin is the kind of bilirubin you want to have if you have to have any because it's more likely to be excreted through the stools. (We want
the bilirubin to be excreted in the poop.) The indirect (unconjugated) bilirubin is the bad kind that hangs around in the body and ends up causing all the problems.
I suggest you find the book:
Handbook of Neonatal Intensive Care
by Merenstein & Gardner ISBN# 0-323-01471-2 for some great information.
I hope my answer was not too confusing and was of some help to you.