Lipoprotein-X levels in extrahepatic versus intrahepatic cholestasis

Lipoprotein-X (LP-X) is an abnormal lipoprotein characteristic of cholestasis. To assess recent claims that its serum concentration helps differentiate extrahepatic from intrahepatic cholestasis, we studied 42 consecutive LP-X-positive patients. The mean serum LP-X level was higher in 18 patients with extrahepatic obstruction than in 24 with intrahepatic cholestatis, 321 +/- 89 versus 130 +/- 31 SEM mg per dl (P less than 0.05). However, values overlapped in 38 of the 42 cases, and in the other 4 the diagnosis of extrahepatic obstruction was obvious anyway from clinical examination. LP-X concentration gave little more information than did free cholesterol of phospholipid levels, which it closely paralleled (r = 0.89 and 0.81, respectively, P less than 0.01). There was no correlation with standard liver function tests or with activity of lecithin-cholesterol acyltransferase, the enzyme responsible for cholesterol esterification in plasma. Contrary to recent claims, these findings suggest that serum LP-X quantitation has little or no clinical value in distinguishing extrahepatic from intrahepatic cholestasis.