Evaluation of the diagnostic value of serum bile acid in the detection and functional assessment of liver diseases

Total serum bile acids or serum bile acid profile, or both, for the diagnosis of intrahepatic cholestasis of pregnancy

BACKGROUND

Intrahepatic cholestasis of pregnancy is a pregnancy-specific liver disorder, possibly associated with an increased risk of severe fetal adverse events. Total serum bile acids (TSBA) concentration, alone or in combination with serum aminotransferases, have been the most often used biomarkers for the diagnosis of intrahepatic cholestasis of pregnancy in clinical practice. Serum bile acid profile, composed of primary or secondary, conjugated or non-conjugated bile acids, may provide more specific disease information.

OBJECTIVES

To assess and compare, independently or in combination, the diagnostic accuracy of total serum bile acids or serum bile acids profile, or both, for the diagnosis of intrahepatic cholestasis of pregnancy in pregnant women, presenting with pruritus. To define the optimal cut-off values for components of serum bile acid profile; to investigate possible sources of heterogeneity.

SEARCH METHODS

We searched the Cochrane Hepato-Biliary Group Controlled Trials Register, the Cochrane Hepato-Biliary Group Diagnostic Test Accuracy Studies Register, the Cochrane Library, MEDLINE Ovid, Embase Ovid, Science Citation Index Expanded, Conference Proceedings Citation Index - Science, BIOSIS, CINAHL, two Chinese databases (CKNI, VIP), Latin American and Caribbean Health Sciences Literature (LILACS), Scientific Electronic Library Online (SciELO), Evidence Search: Health and Social Care by the National Institute for Health and Care Excellence (NICE), the World Health Organization (WHO) Reproductive Health Library (RHL), and the Turning Research into Practice database (TRIP). The most recent date of search was 6 May 2019. We identified additional references by handsearching the references of articles, meta-analyses, and evidence-based guidelines retrieved from the computerised databases, on-line trial registries, and grey literature through OpenSIGLE, National Technical Information Service (NTIS), ProQuest Dissertations & Thesis Database, and Index to Theses in Great Britain and Ireland.

SELECTION CRITERIA

Prospective or retrospective diagnostic case-control or cross-sectional studies, irrespective of publication date, format, and language, which evaluated the diagnostic accuracy of total serum bile acids (TSBA) or components of serum bile acid profile for the diagnosis of intrahepatic cholestasis of pregnancy in pregnant women of any age or ethnicity, in any clinical setting, symptomatic for pruritus.

DATA COLLECTION AND ANALYSIS

We selected studies by reading titles, abstracts, or full texts, and assessing their fulfilment of our inclusion criteria. We emailed primary authors to request missing data or individual participant data. Having extracted data from each included study, we built the two-by-two tables for each primary study and for all the index tests considered. We estimated sensitivity and specificity with their 95% confidence intervals (CI). We presented data in coupled forest plots, showing sensitivities and specificities of each study, and we plotted the studies in the Receiver Operating Characteristic (ROC) space. We performed meta-analyses adopting the hierarchical summary ROC model (HSROC) or the bivariate model to meta-analyse the data. We made indirect comparisons of the considered index tests by adding the index tests as covariates to the bivariate or HSROC models. We performed heterogeneity analysis and sensitivity analysis on studies assessing TSBA accuracy. We used Review Manager 5 (RevMan 5) and SAS statistical software, release 9.4 (SAS Institute Inc., Cary, NC, USA), to perform all statistical analyses. We used QUADAS-2 domains to assess the risk of bias of the included studies.

MAIN RESULTS

Our search yielded 5073 references, but at the end of our selection process, only 16 studies fulfilled the review inclusion criteria. Nine of these provided individual participant data. We analysed only data concerning TSBA, cholic acid (CA), glycocholic acid (GCA), chenodeoxycholic acid (CDCA), and CA/CDCA because the remaining planned index tests were assessed in few studies. Only one study had low risk of bias in all four QUADAS-2 domains. The most biased domains were the patient sampling and the reference standard domains. When considering all studies with a cut-off of 10 μmol/L, TSBA overall sensitivity ranged from 0.72 to 0.98 and specificity ranged from 0.81 to 0.97. After a sensitivity analysis excluding case-control studies, TSBA sensitivity ranged from 0.48 to 0.66 and specificity from 0.52 to 0.99. After a sensitivity analysis excluding studies in which TSBA was part of the reference standard, TSBA sensitivity ranged from 0.49 to 0.65 and specificity from 0.53 to 0.99. We found the estimates of the overall accuracy for some serum bile acid components (CA, GCA, CDCA, and CA/CDCA) to be imprecise, with the CI for sensitivity and specificity very wide or impossible to calculate. Indirect comparisons between serum bile acid profile components and TSBA were not statistically significant. None of the heterogeneity analysis performed was statistically significant, except for the timing of assessment of TSBA (onset of symptoms, peak value among multiple assessments, delivery) but without clinically relevant results. We could not analyse the diagnostic accuracy of combinations of index tests because none of the included studies carried them out, and because of the small number of included studies.

AUTHORS' CONCLUSIONS

The overall high risk of bias, the existing concern regarding applicability of the results in clinical practice, and the great heterogeneity of the results in the included studies prevents us from making recommendations and reaching definitive conclusions at the present time. Thus, we do not find any compelling evidence to recommend or refute the routine use of any of these tests in clinical practice. So far, the diagnostic accuracy of TSBA for intrahepatic cholestasis of pregnancy might have been overestimated. There were too few studies to permit a precise estimate of the accuracy of serum bile acid profile components. Further primary clinical research is mandatory. We need both further phase II and phase III diagnostic studies.

Serum Bile Acids Are Associated with Pathological Progression of Hepatitis B-Induced Cirrhosis

Recent metabonomic studies have identified an important role of bile acids in patients with liver cirrhosis. Serum bile acids, such as glycocholate (GCA), glycochenodeoxycholate (GCDCA), taurocholate (TCA), and taurochenodeoxycholate (TCDCA), increased significantly in liver cirrhosis patients. Our recently published urinary metabonomic study showed that glycocholate 3-glucuronide, taurohyocholate, TCA, glycolithocholate 3-sulfate, and glycoursodeoxycholate (GUDCA) were markedly increased in hepatitis B-induced cirrhotic patients (n = 63) compared with healthy controls (n = 31). The urinary levels of GUDCA were able to differentiate among three stages of cirrhotic patients with Child-Pugh (CP) score A, B, and C. In this study, we recruited two new cohorts of patients with hepatitis-B-induced cirrhosis and healthy control subjects and quantitatively profiled their serum bile acids using ultra-performance liquid chromatography triple quadrupole mass spectrometry. Serum bile acid profile and corresponding differential bile acids were characterized, in addition to the blood routine, liver, and renal function tests. The alterations of bile acids contributing to the intergroup variation between healthy controls and cirrhotic patients and among pathological stages of CP grade A, B and C were also investigated. Five bile acids, GCA, GCDCA, TCA, TCDCA, and GUDCA, were significantly altered among different stages of liver cirrhosis (n = 85), which was validated with an independent cohort of cirrhotic patients (n = 53). Our results show that dynamic alteration of serum bile acids is indicative of an exacerbated liver function, highlighting their potential as biomarkers for staging the liver cirrhosis and monitoring its progression.

Key discoveries in bile acid chemistry and biology and their clinical applications: history of the last eight decades

During the last 80 years there have been extraordinary advances in our knowledge of the chemistry and biology of bile acids. We present here a brief history of the major achievements as we perceive them. Bernal, a physicist, determined the X-ray structure of cholesterol crystals, and his data together with the vast chemical studies of Wieland and Windaus enabled the correct structure of the steroid nucleus to be deduced. Today, C24 and C27 bile acids together with C27 bile alcohols constitute most of the bile acid "family". Patterns of bile acid hydroxylation and conjugation are summarized. Bile acid measurement encompasses the techniques of GC, HPLC, and MS, as well as enzymatic, bioluminescent, and competitive binding methods. The enterohepatic circulation of bile acids results from vectorial transport of bile acids by the ileal enterocyte and hepatocyte; the key transporters have been cloned. Bile acids are amphipathic, self-associate in solution, and form mixed micelles with polar lipids, phosphatidylcholine in bile, and fatty acids in intestinal content during triglyceride digestion. The rise and decline of dissolution of cholesterol gallstones by the ingestion of 3,7-dihydroxy bile acids is chronicled. Scientists from throughout the world have contributed to these achievements.

Serum bile acid concentrations in mild liver cirrhosis

Fasting serum conjugated bile salt concentrations were measured in a group of 20 patients with moderate post-hepatitis cirrhosis. Twenty healthy volunteers were used as controls. The individual conjugated bile acids were analyzed by a specific and sensitive method which couples reversed-phase high-performance liquid chromatography with mass spectrometry. Significantly elevated levels of the total and individual conjugated bile acids were found in cirrhotic patients. The predominant serum bile acids were conjugates of chenodeoxycholic acid. The conjugates of lithocholic acid were also increased; in subjects with normal liver function, on the contrary, they were found only in traces.

Computer simulation of portal venous shunting and other isolated hepatobiliary defects of the enterohepatic circulation of bile acids using a physiological pharmacokinetic model

The effect of three isolated defects in the enterohepatic circulation of bile acids on the size and distribution of the bile acid pool, plasma bile acid levels and bile acid secretion into the intestine was simulated using a linear multicompartmental physiological pharmacokinetic model previously used to simulate these aspects of bile acid metabolism in healthy man. Stepwise increases in portal-systemic shunting (with a reciprocal decrease in hepatic blood flow) caused an exponential increase in systemic plasma concentrations of bile acids, but no other major changes in bile acid metabolism. When the effect of varying fractional hepatic extraction was simulated, it was found that the greater the fractional hepatic extraction, the greater the elevation observed for systemic plasma bile acid levels for a given degree of portal-systemic shunting. When total hepatic blood flow was restored to normal by simulating "arterialization," systemic plasma levels of bile acids decreased strikingly, yet remained elevated. For cholate with a fractional hepatic extraction of 0.9 and 100% portal-systemic shunting, arterialization caused a decrease from a 20-fold elevation to a 5-fold elevation. This simulation thus defined the effect of the presence of the portal venous system per se on plasma bile acid levels and also quantified the circulatory route by which substances reach the liver when portal-systemic shunting is present. An isolated defect in hepatic uptake of bile acids caused little change in overall bile acid metabolism other than modestly increased plasma levels. Loss of bile acid storage by the gallbladder caused the majority of the bile acid pool to move from the gallbladder compartments to the proximal small intestine during fasting but had little effect on the dynamics of the enterohepatic circulation during eating. The results of these novel simulations of isolated defects in bile acid transport should aid in the interpretation of the more complex changes in bile acid metabolism which are likely to occur in hepatic or biliary disease.

Effects of moderate alcohol consumption on platelet aggregation, fibrinolysis, and blood lipids

To investigate the effect of moderate alcohol consumption on blood constituents related to cardiovascular disease, 12 male volunteers consumed (instead of their usual alcoholic drinks) four different standardized amounts of red wine in addition to their habitual diet. Each dose was given to the subjects during a period of 5 weeks in a randomized order, all subjects receiving the four doses. They consisted of 0, 2, and 4 glasses/d, providing 0, 23, and 46 g alcohol/d as well as in "binge drinking" (14 glasses in the weekend, comparable to an average of 2 glasses/d). The results showed a clear dose-related response to the drinking for several blood constituents. Most marked was a decrease in the tissue-type plasminogen activator activity and to a lesser degree an increase in plasminogen levels. Collagen-induced platelet aggregation was reduced, affecting all parameters measured. Levels of HDL3-cholesterol, gammaglutamyltransferase, and urate showed a small but significant increase. No change was noted in the levels of alkaline phosphatase, alanine-aminotransferase, aspartate-aminotransferase, bile acids, folate, fibrinogen, the ADP-induced platelet aggregation, platelet secretion, or in hematologic values. The results are only partially in accordance with the presumed protective action of moderate drinking on the cardiovascular system and show a stronger response to the consumption of alcohol in coagulation and fibrinolysis factors than in blood lipids.

Advances in the application of biochemical tests to diseases of the liver and biliary tract: their role in diagnosis, prognosis, and the elucidation of pathogenetic mechanisms

Despite the biochemical complexity of the liver, few laboratory tests provide discriminatory diagnostic information in patients with hepatobiliary disease. Recent efforts have concentrated upon tests which assess the function of the liver, the severity of the disease state, and underlying pathological processes. Bile Acids: The emergence of facile technology and widespread application has brought the realization that these assays are not as sensitive in detecting liver disease as previously believed, although the cholate/chenate ratio may be useful in distinguishing cholestasis from chronic liver disease. The presence of unusual bile acids in serum or urine may be helpful in some cases. Drug Metabolism: A number of tests provide good evidence about liver function, hepatic blood flow and portal shunting, but the aminopyrine breath tests is the most useful, giving prognostic information in acetaminophen overdose and alcoholic liver disease. The antipyrine half-life identifies surgical cases at risk from poor hepatic function. Proteins and Immunochemical Tests: Interest has developed in plasma proteins such as prealbumin and retinol-binding protein to monitor hepatic protein synthetic function. Secretory IgA is more elevated in biliary tract disease, unlike the native protein which is increased principally in cirrhosis. Type III procollagen can be measured in serum, and correlates with the activity of collagen synthesis and the degree of fibrosis in biopsy samples. Reye's Syndrome: Biochemical tests play an essential role in diagnosis of this recently discovered disease. These will be presented and discussed.