Diagnostic Use
Pancreatic cyst aspirate does not behave like plasma. While serial dilutions of these samples with healthy serum have been made to simulate plasma matrix, routine plasma based methods have not been validated nor are accredited at LabPLUS to measure biomarkers in pancreatic cyst aspirate.
The diagnostic cut points suggested in literature to differentiate mucinous neoplasms (MCN) from non-mucinous conditions like serous cystadenoma (SCA) and pseudocyst varies, likely due to combination of : heterogeneity of inclusion criteria; inter-platform variations in testing non-plasma matrix samples using plasma methods; and non-standardised practices in diluting samples and reporting results.
The points described below therefore only serve as a general guide towards interpretation. They do not necessarily apply to our LabPLUS results. Results should be interpreted in conjunction with cytological, radiological and endoscopic ultrasound findings and other clinical evidences.
A. Amylase =250 U/L is non-diagnostic and does not help in differentiating MCN from SCA or pseudocyst.
B. As a general rule, higher CEA (e.g. >800 ug/L) is more suggestive of a premalignant/malignant MCN and a low CEA (e.g. < 5ug/L) likely indicates a non-mucinous condition. However, there is no single threshold of CEA which can confidently be used to exclude a mucinous lesion or determine its malignant potential.
CEA 192ug/L has about 60-73% sensitivity and 84-93% specificity in identifying MCN
Interpretation of elevated CEA is limited by the significant overlap between individuals
C. A lymphoepithelioid cyst, which is rare but benign, can mimic MCN, with cyst fluid CEA of > 450ug/L.
D. Low levels of CA19-9 <37 kU/L are suggestive of SCA and pseudocyst with one meta-analysis reporting a sensitivity of 19% and specificity of 98%. However, CA19-9 was not identified to be diagnostically superior compared to CEA in a multicentre study. Elevated CA 19-9 level is generally not helpful in differentiating the different cyst pathologies as CA19-9 is a component of normal pancreatic digestive juices.
E. CA125: diagnostically not useful for pancreatic cyst aspirate. Its testing is not offered.
References:
1. ARUP laboratories – Body Fluid Reference Intervals and/ or Interpretive Information for Select Analytes, at https://aruplab.com/bodyfluids (last accessed 25/10/2018).
2. Van der Waaij LA, et al. Cyst fluid analysis in the differential diagnosis of pancreatic cystic lesions: a pooled analysis. Gastrointestinal Endoscopy. 2005 62(3):383-389
3. Linder JD el al. Cyst fluid analysis obtained by EUS-guided FNA in the evaluation of discrete cystic neoplasms of the pancreas: a prospective single-centre experience. Gastrointestinal Endoscopy 2006; 64(5):697-702
4. Brugge WR et al. 2004. Diagnosis of pancreatic cystic neoplasms: a report of the cooperative pancreatic cyst study. Gastroenterology 2004; 126:1330-1336
5. Snozek CLH et al. Use of cyst fluid CEA, CA19-9, and amylase for evaluation of pancreatic lesions. Clinical Biochemistry 2009; 24:1585-1588