In post-hepatic jaundice, the concentration of conjugated bilirubin in the blood is higher than that of unconjugated bilirubin because -
Jaundice

Jaundice is not a disease but rather a sign that can occur in many different diseases.
Jaundice is the yellowish staining of skin and sclerae which is caused by the high level of blood bilirubin.
On the basis of etiology, jaundice can be divided into 3 types : -

1. Prehepatic jaundice

Prehepatic jaundice is due to increased production of bilirubin which results in an increased bilirubin load presented to the liver.
The liver is normal and is able to conjugate the bilirubin at a normal rate; However, due to overproduction of bilirubin, conjugation capacity of the liver is overwhelmed and unconjugated bilirubin is increased → Unconjugated hyperbilirubinemia.
Prehepatic jaundice is caused by hemolysis, i.e., hemolytic anemia due to any cause, e.g., hereditary spherocytosis, Thalassemia, SCA, Malaria, Drugs (methyldopa, quinine) etc.

2. Hepatic jaundice

Here the cause lies within the hepatocytes which have either a defect in the conjugation process or in the excretion of conjugated bilirubin into the bile.
This type of jaundice is caused by all causes of hepatitis (infection, alcohol, drugs, toxin or autoimmune); in congenital hyperbilirubenemias; and in cirrhosis.

3. Post hepatic (extrahepatic) jaundice

Post hepatic jaundice is due to obstruction of the excretion into the bile, e.g., in stone in CBD, carcinoma pancreas, CBD carcinoma etc.
Conjugation capacity of hepatocytes are normal and they continue their conjugation process without any interference leading to conjugated hyperbilirubinemia.
There is an increased rate of destruction of red blood cells.
The unconjugated bilirubin is trapped by the bile stone produced in the bile duct.
The conjugation process of bilirubin in liver remains operative without any interference.
The UDP-glulcuronosyltransferase activity is increased manifold in obstructive jaundice.