ELEVATED LIPASE IN ABDOMINAL PAIN UNUSUAL FOR ACUTE PANCREATITIS: A HIGHER LIPASE THRESHOLD FOR CT SCAN IMPROVES DIAGNOSTIC ACCURACY

Introduction: Previous studies have shown that 8-15% patients with serum lipase >3x upper limit of normal (ULN) diagnosed with acute pancreatitis (AP) may have atypical abdominal pain (PMID: 35523703). While a >3 fold ULN lipase level with typical pain is sufficient to make an AP diagnosis in the absence of imaging; the cutoffs for atypical abdominal pain is unclear. We therefore prospectively analyzed the serum lipase, amylase cutoffs to determine the threshold above which AP could be reliably diagnosed without imaging.

Methods: Split-sample validation was done on 477 prospectively followed patients with serum lipase > 3-fold ULN admitted to Mayo Clinic Arizona between March 2016 and December 2020. The developmental cohort till February 2020 had 338 patients, and the validation cohort had 139 patients. Patient demographics, pain characteristics, lipase levels, imaging findings were documented. Patients were grouped into having typical pain (epigastric) vs atypical pain (diffuse/ localized to one segment other than epigastric/nonacute/nonsevere) vs no pain, and AP vs Non-AP (based on dismissal diagnosis). Receiver operating characteristic (ROC) curves generated cut-offs in the developmental cohort were tested in the validation cohort.

Results: The developmental cohort had 250 typical pain, 33 atypical pain and 55 patients with no pain. 8/33 patients with atypical pain were diagnosed with AP. Non-AP with atypical pain had a lower serum lipase (median 366 U/L, 272-446 U/L interquartile range; IQR), vs. those with AP (985U/L; IQR 643-2114U/L; P<0.003). Lipase >500U/L had a sensitivity of 88%, and specificity of 84% for AP, with a likelihood ratio of 5.5. The validation cohort had 22 patients with atypical pain, with 11 patients being diagnosed with AP. The median lipase in non-AP patients with atypical pain was lower (383 U/L; IQR 293-401 U/L), than those with AP (2109U/L; IQR 699-3000U/L), and identified 10/11 AP patients while none of the 11 non-AP patients was falsely identified. The sensitivity of (91%), specificity (100%) area under the curve of 0.99 (confidence interval 0.96-1.00) were acceptable. There were no differences in Age, Sex, BMI in AP vs. non-AP patients with atypical pain in either cohort. Serum lipase values in the painless groups (n=79 patients) did not differ in those without AP (median 383U/L; 287-629 U/L) from AP patients (519U/L; 398-3000 U/L; p=0.06).

Conclusions: A lipase value of >500U/L (>8 fold ULN) may help in making a diagnosis of AP in patients with atypical abdominal pain with high accuracy. While our study is small and from a single center, it suggests that larger studies at other centers could be done to validate our findings. This may help in reducing the burden of cross-sectional imaging required to make a diagnosis of AP in the 8-15% patients who present with atypical abdominal pain.