GS is often diagnosed in your late teens and early twenties. In most cases doctors should be able to establish diagnosis on the basis of liver function tests (LFTs) and jaundice, if you have it.
Sometimes – but rarely – a blood test is taken before and after a 48 hour diet in which you are required to reduce your calorie intake. In people with GS a significant increase in their bilirubin levels is usually seen to follow this.
Liver function tests are used to indicate whether your liver is inflamed (hepatitis), damaged or not working properly. They measure levels of certain enzyme and protein substances in your blood that may alter when liver damage is present.
Liver function tests also measure the amount of bilirubin to gain an indication of your liver’s ability to metabolise and secrete it into bile. The ‘serum bilirubin test’ is considered to provide a very accurate picture of how well the liver is functioning.
Raised and heavily unconjugated bilirubin in your blood is abnormal. When this is the only abnormal result, it is seen as a strong indication that you may have GS. Bilirubin levels can, however, fluctuate in GS and it is possible that they can be within the normal range over a period of time.
Bilirubin is measured in millimoles per litre (umol/L). Total serum bilirubin higher than 17 umol/L is outside the normal range.
Where jaundice is evident, medical staff may seek diagnosis by excluding more serious forms of liver disease. GS is one of the most common causes of unconjugated hyperbilirubinemia, but there are others. These include a rare and dangerous disorder called Crigler-Najjar syndrome which is inherited from the same gene.
If your diagnosis involves further testing or delay of some sort you may experience some anxiety before other possibilities can be ruled out.
For this reason it is important that doctors diagnose GS as soon as possible.