Unconjugated bilirubin

What is unconjugated bilirubin?

Every day your spleen clears old red blood cells, and from the haemoglobin in them bilirubin is released, the yellow waste pigment. In that first form it does not dissolve in water; it travels bound to albumin to your liver, where an enzyme attaches sugar groups to it, which is called conjugating. Only then can it go through the bile into your gut. Everything that has not yet had that processing is called unconjugated bilirubin, and that is normally the largest part of what circulates in your blood. The part is not measured but calculated: total bilirubin minus conjugated bilirubin, both from the same tube. It is the fraction that holds the most common explanation for a slightly raised bilirubin. In Gilbert's syndrome, an inborn variant found in about one in twenty people, the enzyme that attaches the sugar groups works at half strength, and precisely this part accumulates while the conjugated part stays neatly low. The same happens in everyone after a night of fasting, poor sleep or heavy exertion, because then the enzyme gets less fuel. Your report prints it in µmol/L, sometimes as indirect bilirubin, which is the same; otherwise you calculate it with the calculator on this page. There is no band, because it is a subtraction. What you do have are the bands of the two values beneath it: 19 to 24 µmol/L as the upper limit for the total and 3.4 to 5 for the conjugated part, depending on your lab. A low number is naturally low and says nothing.

Why is unconjugated bilirubin relevant?

This is the part that answers whether a raised bilirubin means anything. If mainly the unconjugated part is high while the conjugated part stays low and the liver values are normal, the explanation is almost always Gilbert's syndrome or a night of fasting, and then nothing is wrong. Anyone who knows that once does not need to be alarmed again at every slight rise. The second reason is that the part says something about the balance between breakdown and processing. If it rises without Gilbert and without fasting, more red blood cells are being broken down than the liver can keep up with, and then haemoglobin, reticulocytes and LDH belong with it. That is rare, but it is why the part is always looked at separately when the total is raised. The honest limitation is that it is a subtraction and not a measurement, without a band of its own. It moves with everything that moves the total and the conjugated part, and it is the part fasting lifts, so a fasting draw makes it come out higher than an ordinary one. Always read it beside the total and the conjugated part, because the ratio between the two carries the meaning.

How unconjugated bilirubin is worked out

None of the four labs publishes a band for this fraction, and that follows from what it is: a calculation and not a measurement. Unilabs carries the entry but leaves the band empty and notes that the test cannot be requested on its own; Certe carries it under the name indirect bilirubin without a band; Star-shl and Clinical Diagnostics do not carry the fraction. What you do have are the bands of the two values beneath it: 19 to 24 µmol/l as the upper limit for the total and 3.4 to 5 for the conjugated part, depending on your lab. A total slightly above the band while the conjugated part is low and the liver values are normal is the picture of Gilbert or of a night of fasting.

Unconjugated bilirubin high or low: what it means

A low unconjugated bilirubin is naturally low and says nothing: your spleen breaks down red blood cells at an ordinary pace and your liver keeps up. There is no lower limit and no deficiency exists. A high unconjugated bilirubin means more production or slower processing. From common to rare: Gilbert's syndrome, the harmless inborn variant in which the enzyme works at half strength and total bilirubin is slightly raised with otherwise normal liver values; fasting or a night of poor sleep, because then the enzyme gets less fuel and this part rises in everyone, even without Gilbert; liver strain, through alcohol, fat, a virus or a medicine, where the conjugated part and ALT also rise; and rarely accelerated breakdown of red blood cells, where haemoglobin falls and reticulocytes and LDH rise. What you do about it: with Gilbert nothing, except knowing you have it and that fasting, illness and heavy exertion lift it temporarily; some medicines are broken down more slowly with Gilbert, and that is worth mentioning with a new prescription. If you want to compare the number with an earlier result, have blood drawn after an ordinary breakfast and not after a night without food. If the conjugated part or ALT rises too, what holds for any liver strain holds here: no alcohol, losing weight in fatty liver and checking which medicines you use. Set unconjugated bilirubin beside the total and the conjugated part, because the ratio carries the meaning, beside ALT and gamma-GT, which show whether the liver is strained, and beside haemoglobin and reticulocytes if the part rises without Gilbert and without fasting.

How does an unconjugated bilirubin blood test work?

Referral

Not needed, but this part cannot be requested on its own either: you request the total and the conjugated part, and you calculate the difference with the calculator on this page.

Fasting

Not needed, and even unwise if you want to compare the value: fasting lifts precisely this part. Have blood drawn after an ordinary breakfast.

When

As soon as total bilirubin is raised and the question is which fraction it is. Not after a night of poor sleep, heavy exertion or a lot of alcohol, because those lift it temporarily.

The draw

One tube of blood from a vein in your arm, from which total and conjugated both come; otherwise the difference is not a fraction but a time difference. The tube belongs in the dark, because bilirubin breaks down in daylight.

Repeating

With Gilbert not needed; anyone who knows it once does not need to have blood drawn again at every slight rise. If the part rises without Gilbert and without fasting, repeat with ALT, haemoglobin and reticulocytes added.

Where to draw

You can draw at 250+ locations near you, no referral needed. See the locations

Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.