CEA, AFP and CA 19-9 analysis in peritoneal fluid to differentiate causes of ascites formation
Highlights
► CEA, CA 19-9 and AFP were measured in ascites to identify malignancy. ► Cut-offs were established, and diagnostic performance was evaluated. ► Subset analysis based on malignancy type was performed for each tumor marker. ► We report the utility of CEA, CA 19-9 and AFP to be used complementary to cytology.
Introduction
Ascites is a pathological condition described by fluid accumulation in the peritoneal cavity. Although cirrhosis and portal hypertension are the main causes of ascites (~ 85% of cases), malignant conditions, such as peritoneal carcinomatosis, and other metastatic carcinomas within the peritoneal cavity may be the reason [1]. Accumulation of fluid in these conditions can be due to blockage of the lymphatic system, secondary portal hypertension, and increased vascular permeability as a consequence of tumor obstructions.
The current strategy for identifying malignancy-associated ascites focuses on the use of cytological analysis of peritoneal fluid. This relies on the presence of malignant cells that have been sloughed off into the abdominal fluid, which must then be detected on a smear. While this is a practical approach for some cases, specifically for peritoneal carcinomatosis which accounts for 53% of malignancy-associated ascites, other malignancies, such as hepatocellular carcinoma, metastatic carcinoma to the liver, or chylous ascites due to malignancy may be problematic since these are less likely to have cell shedding [2]. The specificity for cytological analysis is very high, but the lack of cell exfoliation in all malignancies lowers the sensitivity of cytology to 40–60% [3]. In these situations, it is advantageous to utilize other testing strategies for characterizing the cause of peritoneal fluid accumulation.
Measurement of tumor markers in peritoneal fluid is often used to aid in differentiation of non-malignant from malignancy-associated ascites, especially in cases where cytology is uninformative. The utility of carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA 19-9), and alpha-fetoprotein (AFP) in differentiating malignancy from non-malignant ascites has been controversial due to conflicting findings, and in some cases, low sensitivity and specificity of these markers [4], [5]. This may be due, in part, to the heterogeneity in the types of malignancies used in the evaluation. An improvement on these studies lies in subtype analysis by correlating tumor marker values with malignancies known to have elevations of these antigens in serum. This has shown to improve sensitivity in tumor marker analysis in pleural fluid [6].
The aim of this study was to correlate cytological findings with tumor marker analysis as a way to improve the differentiation of malignancy-associated ascites from non-malignant ascites. Cut-off values that provide high specificity were established and each tumor marker was assessed for diagnostic performance in malignancies known to secrete the tumor marker in serum.
Section snippets
Patients
The Mayo Clinic Institutional Review Board approved this study. Peritoneal fluid samples were collected from 137 patients (66 males and 71 females) seen at Mayo Clinic, Rochester, MN between May 2011 and December 2011 and underwent a paracentesis for cytology evaluation. A designation of non-malignant (n = 83) or malignant (n = 54) was made for each sample based on cytology findings, biopsy results and long-term follow-up care. Clinical findings were reviewed in the medical record for each patient
Results
Since CEA, CA 19-9 and AFP immunoassays are not currently FDA cleared for use in peritoneal or other body fluids, validation studies were performed. Accuracy, intra- and inter-assay precision, limit of detection, limit of quantitation, reportable range and interference studies were assessed, the results of which can be found in Table 2.
A total of 137 ascites samples were utilized in this study. The concentrations of CEA, CA 19-9 and AFP in malignant ascites were significantly higher than in
Discussion
Analysis of CEA, CA 19-9 and AFP was performed to determine their usefulness in distinguishing non-malignant from malignant etiologies of ascites. Analysis was performed using tumor marker cut-offs that achieved high specificity to reduce false positives that might lead to additional unnecessary testing; as a consequence, the sensitivities were lower than previous reports [5], [14], [15]. Using this approach, measurement of tumor markers did not show improved sensitivity over cytology when all
Conclusions
Overall, this study enhances the understanding of the utility of CEA, CA 19-9 and AFP in the classification of non-malignant and malignant ascites. When applied to all malignant causes of ascites, the sensitivity of the tumor markers was limited. However, when the analysis was tailored to those malignancies that are known to secrete these tumor markers in the serum, the performance of the tests improved. Therefore, narrowing tumor marker testing based on the patient's diagnosis differential and
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