Direct (conjugated) bilirubin: what a raised result points to

Red blood cells live for about 120 days. When they are broken down, haemoglobin is released and converted into unconjugated (indirect) bilirubin. Lab Tests Online UK explains that the liver then adds sugars to it, creating conjugated (direct) bilirubin, which is secreted into bile and passes to the intestines, where bacteria break it down further and eventually produce the brown colour of normal stools.

Small amounts of unconjugated bilirubin are found in blood but virtually no conjugated bilirubin should be present. That is why a measurable direct bilirubin is a more specific flag than the total.

The test usually measures total bilirubin first. If the total is raised, the laboratory or doctor may ask for separate conjugated and unconjugated measurements, called a split bilirubin, to work out the cause. Lab Tests Online UK lists symptoms prompting bilirubin testing: yellowing of the skin or eyes, dark amber urine, pale stools, itching, nausea and vomiting, abdominal pain or swelling and fatigue. It is also used for people who drink excessive alcohol, have been exposed to hepatitis viruses, take medicines that affect the liver, or have anaemia caused by red cell destruction.

In infants with jaundice, conjugated bilirubin is often requested along with the total, because a raised conjugated fraction needs prompt investigation.

No special preparation is needed. Blood is drawn from a vein in the arm. For newborns a few drops of blood are taken by heel prick, and sometimes a transcutaneous meter on the skin estimates the level, although this may need a blood test to follow up. The sample can be protected from bright light before testing, since light breaks down bilirubin.

According to Lab Tests Online UK, high conjugated bilirubin may indicate a blockage of the liver or bile ducts, hepatitis, liver trauma, cirrhosis, gallstones, a drug reaction or long-term alcohol abuse. Because conjugated bilirubin is water soluble, some passes into the urine when blood levels are high, darkening it, while less reaches the gut so stools become pale.

Doctors combine the result with ALP and GGT, which rise when bile ducts are blocked. A raised bilirubin with a markedly raised ALP and itching points toward obstruction or cholestasis, while a raised bilirubin with very high ALT points toward hepatitis.

Newborns commonly have slightly raised bilirubin between days 2 and 7, called physiological jaundice, because the liver is not yet mature enough to process it quickly. Lab Tests Online UK says up to half of full-term babies develop it. Jaundice is concerning if it appears within the first 24 hours, or persists beyond 8 to 14 days.

Persistent jaundice may reflect abnormal liver metabolism or malformed bile ducts, such as biliary atresia, which needs early surgical treatment to avoid the need for a liver transplant. Very high unconjugated bilirubin in newborns can damage developing brain cells, so treatment with phototherapy or exchange transfusion may be used. Any baby who looks yellow after the first two weeks, or has pale stools or dark urine, needs medical review.

For a raised direct bilirubin, the usual next steps are a full liver panel, an ultrasound of the liver and bile ducts, tests for hepatitis and a medicines review. Jaundice with fever, severe abdominal pain, confusion or vomiting blood needs same-day emergency care; call 999 or attend A&E.