Q&A: Diagnosing Cause of Jaundice

The normal serum bilirubin concentration in children and adults is less than 1 mg/dL (17 micromol/liter), less than 5 percent of which is present in conjugated form. The measurement is usually made using diazo reagents and spectrophotometry. Conjugated bilirubin reacts rapidly ("directly") with the reagents. The measurement of unconjugated bilirubin requires the addition of an accelerator compound and is often referred to as the indirect bilirubin.

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This is a Question & Answer revision article designed for medical students and professionals preparing for the PLAB, MRCP or USMLE examinations. They are based on actual questions from these examinations. You may find the Digestive Health article more useful, or one of our many articles on Diseases & Conditions, Medical Syndromes, Health & Wellness or Home Remedies.

In this article:
Classification of jaundice
MCQ: clinical scenario
MCQ: answer
MCQ: explanation

Classification of jaundice

Jaundice is often used interchangeably with hyperbilirubinemia. However, a careful clinical examination cannot detect jaundice until the serum bilirubin is greater than 2 mg/dL (34 micromol/liter), twice the normal upper limit. The yellow discoloration is best seen in the periphery of the ocular conjunctivae and in the oral mucous membranes (under the tongue, hard palate). Icterus may be the first or only sign of liver disease; thus its evaluation is of critical importance.

For clinical purposes, the predominant type of bile pigments in the plasma can be used to classify hyperbilirubinemia into two major categories:

• Plasma elevation of predominantly unconjugated bilirubin due to the overproduction of bilirubin, impaired bilirubin uptake by the liver, or abnormalities of bilirubin conjugation
• Plasma elevation of both unconjugated and conjugated bilirubin due to hepatocellular diseases, impaired canalicular excretion, defective reuptake of conjugated bilirubin and biliary obstruction.

In some situations, both overproduction and reduced disposition contribute to the accumulation of bilirubin in plasma.

MCQ: clinical scenario

A 70 year old man presents to his general practitioner complaining of dull and boring pain which radiates to the back. He has found that the pain intensifies on lying down and tends to be relieved by crouching forward. On questioning he admits to smoking 25 cigarettes daily,and to losing 12 pounds(5 kg) over the last 2 months. On examination he is found to be cachexic, he was afebrile, and appears jaundiced. Abdominal palpation reveals a mass in the upper abdomen under the right costal margin.

The most likely cause for this man's jaundice is:

a) a malignant lesion of the head of the pancreas
b) stones in the common bile duct
c) hepatocellular carcinoma
d) hepatitis B
e) gall bladder carcinoma

MCQ: answer

The correct answer is B

MCQ: explanation

Pancreatic cancer is the 4th most common cancer causing death in the U.S. The disease is more common in men especially those between 60 and 70 years. The cause is unknown, but the incidence is greater in smokers. In fact cigarette smoking is one of the greatest risk factors for the development of cancer of the pancreas.

Rapid spread: Most of the carcinomas of the pancreas are advanced by the time they cause symptoms. Pain in the back and upper abdomen occurs when a pancreatic tumor presses against the nerves in those areas. The disease is not only common, but it is also extremely difficult to treat. The most commonly occurring cancers of the pancreas tend to grow rapidly. More than 90 percent of them arise in the ductal cells, which transport digestive enzymes to the duodenum. Two- thirds of ductal cell tumors grow in the head of the pancreas; the other third develop in the gland's body and tail. A large firm liver eventually develops due to seeding.

Reference(s)
1). UpToDate: Classification and causes of jaundice or asymptomatic hyperbilirubinemia. Available online: https://www.uptodate.com/contents/classification-and-causes-of-jaundice-or-asymptomatic-hyperbilirubinemia