Tuesday, April 1, 2008

Bilirubin made EZ

Ah good ole Bilirubin. One of those famous lab values that seems so important to so many people, but why? Understanding this simple lab concept can not only help you when it comes to NCLEX or USMLE time, but will help you as an RN, ARNP or MD to recognize certain pathologies that you will frequently encounter.

OK, lets take a look at Bilirubin in general. On most circulations through the body, RBCs have to pass through the ultimate inspection. They file through tight spaces in the spleen and are closely inspected by the watchful eye of WBCs. Any weakness is immediately noticed, and that poor RBC is bound for destruction. Their life is on average, only 40 days, and then they suffer an awful end. When they are ripped out of line, they have their core of iron ripped out to be recycled, and their skin stripped off and dumped. Talk about a bad way to go. This skin is the origin of what we see in a lab value as Bilirubin. At this point, it is simply unconjugated Bilis, often termed indirect bilirubin. It is dumped into the drainage system of the spleen, which is the bloodstream that leads to the liver, known as the Portal system. When it reaches the liver, it is then conjugated, which simply means the liver alters the structure a little bit, and we now have conjugated or direct bilirubin. This new product is now stored in the gall bladder to be used as bile salts. Bile salts are released when you eat a fatty meal, and assist the body in absorbing the fat molecules. Unabsorbed Bile salts are broken down by bacteria in your gut, and are what make your stool brown.

OK got that picture in your head? Heres how knowing this helps. If Bilirubins become elevated in the blood stream, it is usually because the liver is too congested to accept new deliveries, and they then build up in the bloodstream causing pruritis, yellow jaundice skin and sclera, and give their brown color to the urine. Meanwhile the stool is a light color with no bilis, and fat is not absorbed.

But there is more. I can use this lab value to tell what the cause of that liver congestion is. If the liver itself is the blame, such as in the case of Liver diseases like Cirrhosis, any new bilirubin is not conjugated, so I will get UNconjugated or Indirect bilirubins that are elevated. On the other hand if the Bile duct is the source of the back up congestion in the liver, the new bilis are conjugated by the liver, but can not pass on into the gall bladder or GI tract, so Conjugated or Direct bilirubins are elevated in the blood. Make sense? So don't just be satisfied to know that bilirubin is elevated, but look closer and see what type of bilirubin is elevated, and you will have a very good idea if this is a liver dysfunction or a biliary obstruction...big difference right!?

OK. One other thing you will see in the picture below. Another way you can have elevated bilis is if you are simply killing way too many RBCs, and your liver can't keep up with the delivery. This would happen in the case of Hemolysis, where RBCs are actively being destroyed in great numbers.

Check out these cheesy drawings, and hopefully they will truly be worth a 1000 words.

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