Bilirubin

A red blood cell lasts about four months. Then it is broken down in your spleen, and the haemoglobin released is converted into bilirubin, a yellow substance that does not dissolve in water. Bound to albumin it travels to your liver, which attaches a sugar group so it becomes soluble, and then drains it through the bile into your gut, where it gives your stool its colour. What circulates in your blood is the sum of the part still waiting for the liver and the part already processed. A high bilirubin therefore has three possible places. Too much supply, when red cells are broken down faster than normal; a liver that does not keep up the processing, through an inherited variant or through liver cell damage; or a drainage that is stuck, through gallstones or a narrowing. The other liver values point the way: ALT and AST high is the liver cell, ALP and gamma-GT high is the drainage, and all normal with many reticulocytes is breakdown. Your report shows bilirubin in µmol/L. Normal is about 4 to 20 µmol/L for a man and 3 to 19 µmol/L for a woman from age 19. Above about double that the whites of the eyes turn yellow; well below that a rise is only visible on paper.

The reason bilirubin is interesting for anyone healthy is that a slight rise is almost always Gilbert's syndrome. About one in twenty people has an inherited variant of the enzyme that makes bilirubin soluble, and it works somewhat more slowly as a result. The value then sits naturally at the high end and peaks with fasting, a night of poor sleep, an infection or hard exertion, sometimes to a slight yellow tint of the whites of the eyes. It is not a disease and it asks for nothing. More than that: people with Gilbert's have in research actually less cardiovascular disease, because bilirubin is an antioxidant. Anyone who knows it never has to be startled by it again. The second reason is that bilirubin is the last liver value to rise. Gamma-GT, ALT and ALP respond to strain; bilirubin only rises once the liver really no longer keeps up the drainage. A high bilirubin beside a high ALT or ALP is therefore a more serious picture than those values alone, and a normal bilirubin with a raised ALT is reassuring. The third reason is the supply. If red cells are broken down too fast, in haemolysis, bilirubin rises together with LDH and the reticulocytes, while the liver values stay normal. In anyone who runs a lot that happens in a small way with every footstrike, and a bilirubin at the high end belongs to that picture.

A high bilirubin means too much supply, a liver that does not keep up or a drainage that is stuck. Usually it is the first and rarely the last: Gilbert's syndrome, fasting or a night of poor sleep, liver strain from alcohol, medicines or a virus, bile congestion, and rarely an accelerated breakdown of red blood cells. The other values point the way. Only bilirubin slightly raised, everything else normal: Gilbert's or fasting, and a repeat after normal eating and sleeping lets it fall. Bilirubin high with high ALT and AST: the liver cell. Bilirubin high with high ALP and gamma-GT, and dark urine and pale stool: the drainage, and then time counts. Bilirubin high with high LDH and many reticulocytes: breakdown. A low bilirubin means nothing; it is not a deficiency and nothing belongs with it. Bilirubin belongs beside ALT, AST, gamma-GT and ALP, and with a rise without a liver picture beside LDH and the reticulocytes. Do not fast longer than an ordinary night, because fasting lifts the value.