Jaundice is the symptom and sign of skin, mucosa and sclera are stained yellow because of the elevation of bilirubin in serum. What we should pay attention to is that "stained yellow" mentioned above is homogeneous stained and sclera yellowing is a characteristic change of jaundice. From this definition, we can know that jaundice is not a disease, but a symptom(refers to what patients can feel subjectively) and sign(means abnormal changes discovered by doctors when they check their patients). And we can see a key word––bilirubin, so let's keep our eyes on this important pigment first.
Bilirubin is a metabolic of protoheme with golden yellow, and it's the main pigment in bile. The metabolism of bilirubin is quite a complex progress, including producing, transporting, combining with UDP-glucuronic acid and then forming conjugated bilirubin(CB), if bilirubin is not combined, we call it unconjugated bilirubin(UCB). With bile, CB is easily discharged into small intestine and continues to be metabolized, some of the metabolites go back to the liver(enterohepatic circulation), the rest will be excreted with urine(urobilin) or with faeces(stercobilin). Besides, only CB can be excreted from urine through the glomerular basement. CB plus UCB is called STB(serum total bilirubin).
The reference ranges are:
STB: 3.4~17.1μmol/L
CB: 0~6.8μmol/L
UCB: 1.7~10.2μmol/L
If STB is above17.1μmol/L but below 34.2μmol/L, there is no visible yellowing sclera or skin, it is called latent jaundice.
If STB is above 34.2μmol/L, sclera、skin or mucosa are obviously stained yellow.
According to the cause and mechanism of jaundice, it can be divided into three types.
①Hemolytic jaundice
It is also known as prehepatic jaundice.There are so many red blood cells are destroied due to favism, some drugs or poisons that mononuclear phagocytic system produces an excess of bilirubin which is beyond of the ability of the liver. So the result of it is UCB in serum elevating a lot. Except stained yellow, the color of the patient's faeces also deepened.
②Hepatocellular jaundice
We also call it hepatogenic jaundice. Because of the function of hepatic cells are damaged, liver's uptake, transformation and excretion of bilirubin decreased and then cause hyperbilirubinemia. This kind of jaundice will lead to a light color of stool.
③Obstructive jaundice
It means posthepatic jaundice.There are many causes can lead to this type of jaundice, such as calculus of bile duct, pancreatic head carcinoma, liver fluke and so on. As long as the bile duct is obstructed and bile can't excrete into duodenum, obstructive jaundice will happen. The color of stool will turn to be light. If the bile duct is completely obstructed, it will become clay colored stool.
Neonatal jaundice is the most common clinical problem among newborns. The measure we usually take inour country is exposing the baby to blue light.
