Diagnostic Testing


Diagnostic Testing

Diagnostic Testing for Cholestasis of Pregnancy

Cholestasis is diagnosed by bloodwork. The test that is used is a “Total Bile Acid” test. Liver function tests are also usually run (AST, ALT) but these are not diagnostic of cholestasis and the bile acid test must be run for diagnosis.

There are several different bile acid tests from different laboratories that are all run a little differently. These will each therefore have different reference ranges listed.

The main types of tests are:

  • Enzyme tests: Labcorp and Mayo are the two major labs that run an enzyme test. Reference range is 0-10.
  • Quest Bile Acids, Total: This test is run by spectrophotometry and has a listed reference range of 0-19. Of note, this is a non-pregnancy reference range but this test can be used in pregnancy which will be described below.
  • Quest Bile Acids, Fractionated and Total: otherwise sometimes known as “Bile Acids, Pregnancy”: This test is run by Chromatography/Mass Spectrometry and has a reference range of <8.3. It measures and reports the levels of a few different bile acids including ursodeoxycholic acid (ursodiol).

Studies comparing women with cholestasis to pregnant women without cholestasis have found that a level of 10 µmol/L is usually diagnostic for cholestasis. Most women with normal pregnancies had bile acids below this level and most women with cholestasis had levels above this level.1,2,3  SMFM which is the governing board for High Risk OB physicians in the US states that above 10 is diagnostic of cholestasis.4

You do not have to have a specific type of bile acid test run in pregnancy. There is often confusion that you can only have the pregnancy bile acid test from Quest. This is incorrect. Any of these total bile acid tests can be used to diagnose cholestasis. In fact, studies have verified that many different tests are accurate for diagnosis. 2,3

The confusion often comes as many OB physicians will only see a few cases of cholestasis in their careers. Often, they will go by the reference range of the test. Therefore, a lot of women who really have cholestasis with a level above 10 on a certain test with a higher reference range will fail to be diagnosed. This happens most often on the Quest Total Bile Acid test with its reference range of 0-19. You CAN be diagnosed on this test if your levels are above 10 µmol/L. However, some physicians are either unaware of this fact or will not diagnose based on this.

If you have elevated levels (above 10) and are not being diagnosed, you could request to have one of the other bile acid tests drawn for comparison and possible diagnosis. Of note, taking ursodiol can lower bile acids also and lead to not being diagnosed. Discuss with your physician retesting options if you are already on ursodiol.

However, if your physician will diagnose you on the total bile acid test, you do not need to have the pregnancy specific test performed. Any of the tests are valid for diagnosis.

10/16/20

References

  • Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009 Dec;114(6):1326-31. doi: 10.1097/AOG.0b013e3181c2bde8. Erratum in: Obstet Gynecol. 2010 Feb;115(2 Pt 1):387. PMID: 19935037.
  • Egan N, Bartels A, Khashan AS, Broadhurst DI, Joyce C, O’Mullane J, O’Donoghue K. Reference standard for serum bile acids in pregnancy. BJOG. 2012 Mar;119(4):493-8. doi: 10.1111/j.1471-0528.2011.03245.x. Epub 2012 Jan 18. PMID: 22251417.
  • Lee RH, Ouzounian JG, Goodwin TM, et al: Bile acid concentration reference ranges in a pregnant Latina population. Am J Perinatology 2013;30(5):389-393.
  • Understanding Intrahepatic Cholestasis of Pregnancy – Publications SMFM.org – The Society for Maternal-Fetal Medicine. Smfmorg. 2015. Available at: https://www.smfm.org/publications/96-understanding-intrahepatic-cholestasis-of-pregnancy