Direct bilirubin is the sum of the conjugated fractions. Direct bilirubin is elevated in conditions causing hepatic obstruction, hepatitis, cirrhosis, several inherited enzyme deficiencies, and inherited defects in canalicular excretion.

Lt green plasma separator (PST)

Immediately after collection, mix tube thoroughly by gentle inversion, 8 - 10 times, to prevent clotting

• Spin within two (2) hours of sample collection
• Protect specimen from bright light as bilirubin is photolabile. Exposure to direct sunlight can decrease bilirubin in samples by 50% within one hour.

Lt green plasma separator (PST)

Gold serum separator (SST) tube

Microtainer - amber serum separator (SST), with extender

Neonatal bilirubin samples should be collected into an amber microtainer. If no amber microtainer is available, samples should be protected from light by wrapping in aluminum foil during transport to the testing facility

Immediately following collection, thoroughly mix sample by gently inverting 5 times

1. Allow sample to clot for a minimum of 30 minutes
2. Spin within two (2) hours of sample collection

Gold serum separator (SST) tube

False bottom plasma/serum transport vial/tube (AHL)

Refrigerated (preferred) - 7 days

Ambient - 2 days

Frozen - 6 months

• Improper labels (unlabeled or mislabeled)
• Hemolysis (some procedures)
• Improper anticoagulant or ratio
• Delay in transport
• Improper storage temperature affecting results
• Improper container
• Leaking container resulting in compromised specimen
• Quantity not sufficient (QNS)

Endpoint Colorimetric with Diazo

0.0 - 0.3 mg/dL

Red blood cells at the end of their circulating life are broken down in the reticuloendothelial system, mainly the spleen. The resulting heme, once the iron is removed, is then converted to bilirubin. This process accounts for about 80% of the 500 μmol (300 mg) of bilirubin formed daily. Other sources of bilirubin include the breakdown of myoglobin and cytochromes and the catabolism of immature red blood cells in the bone marrow.

Once formed, bilirubin is transported to the liver bound to albumin. This fraction of bilirubin is referred to as indirect or unconjugated bilirubin. In the liver, bilirubin is conjugated to glucuronic acid (mono- and di-glucuronides) to form conjugated bilirubin by the enzyme uridyl diphosphate glucuronyl transferase. Conjugated bilirubin or direct bilirubin is excreted via the biliary system into the intestine, where it is metabolized by bacteria to a group of products known collectively as stercobilinogen. Elimination is almost complete and serum levels are normally negligible.

Direct bilirubin is the sum of the conjugated fractions. Direct bilirubin is elevated in conditions causing hepatic obstruction, hepatitis, cirrhosis, several inherited enzyme deficiencies, and inherited defects in canalicular excretion.