Review of imaging findings in hepatic veno-occlusive disease.

Hepatic veno-occlusive disease (VOD), also known as sinusoidal obstruction syndrome (SOS), is a potentially life-threatening complication of hematopoietic stem cell transplantation. Patients present with right upper-quadrant abdominal pain, jaundice, weight gain, and conjugated hyperbilirubinemia. Early diagnosis of VOD is essential to promptly initiate defibrotide therapy, which has been demonstrated to enhance survival and achieve complete resolution of disease in some patients. Historically, VOD was diagnosed by the modified Seattle or Baltimore criteria, which are both based on clinical symptoms. Alongside advancements in medical imaging over the last 40 years, the diagnosis of VOD has evolved to include the use of ultrasound, elastography, cross-sectional imaging, and image guided biopsy. Identification and interpretation of findings of VOD across imaging modalities is now a critical aspect of post-HSCT care. This review will outline the imaging findings and recommendations for the use of imaging in the management of VOD including gray-scale, color and spectral Doppler ultrasound, ultrasound elastography, CT, MRI, and liver biopsy.

Programmed Death Ligand-1 and Tumor Mutation Burden Testing of Patients With Lung Cancer for Selection of Immune Checkpoint Inhibitor Therapies: Guideline From the College of American Pathologists, Association for Molecular Pathology, International Association for the Study of Lung Cancer, Pulmonary Pathology Society, and LUNGevity Foundation.

CONTEXT.­: Rapid advancements in the understanding and manipulation of tumor-immune interactions have led to the approval of immune therapies for patients with non-small cell lung cancer. Certain immune checkpoint inhibitor therapies require the use of companion diagnostics, but methodologic variability has led to uncertainty around test selection and implementation in practice. OBJECTIVE.­: To develop evidence-based guideline recommendations for the testing of immunotherapy/immunomodulatory biomarkers, including programmed death ligand-1 (PD-L1) and tumor mutation burden (TMB), in patients with lung cancer. DESIGN.­: The College of American Pathologists convened a panel of experts in non-small cell lung cancer and biomarker testing to develop evidence-based recommendations in accordance with the standards for trustworthy clinical practice guidelines established by the National Academy of Medicine. A systematic literature review was conducted to address 8 key questions. Using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach, recommendations were created from the available evidence, certainty of that evidence, and key judgments as defined in the GRADE Evidence to Decision framework. RESULTS.­: Six recommendation statements were developed. CONCLUSIONS.­: This guideline summarizes the current understanding and hurdles associated with the use of PD-L1 expression and TMB testing for immune checkpoint inhibitor therapy selection in patients with advanced non-small cell lung cancer and presents evidence-based recommendations for PD-L1 and TMB testing in the clinical setting.

Principles of Analytic Validation of Immunohistochemical Assays: Guideline Update.

CONTEXT.­: In 2014, the College of American Pathologists developed an evidence-based guideline to address analytic validation of immunohistochemical assays. Fourteen recommendations were offered. Per the National Academy of Medicine standards for developing trustworthy guidelines, guidelines should be updated when new evidence suggests modifications. OBJECTIVE.­: To assess evidence published since the release of the original guideline and develop updated evidence-based recommendations. DESIGN.­: The College of American Pathologists convened an expert panel to perform a systematic review of the literature and update the original guideline recommendations using the Grading of Recommendations Assessment, Development and Evaluation approach. RESULTS.­: Two strong recommendations, 1 conditional recommendation, and 12 good practice statements are offered in this updated guideline. They address analytic validation or verification of predictive and nonpredictive assays, and recommended revalidation procedures following changes in assay conditions. CONCLUSIONS.­: While many of the original guideline statements remain similar, new recommendations address analytic validation of assays with distinct scoring systems, such as programmed death receptor-1 and analytic verification of US Food and Drug Administration approved/cleared assays; more specific guidance is offered for validating immunohistochemistry performed on cytology specimens.

Perioperative Chemotherapy and Chemoradiotherapy for Patients With Resectable and Borderline Resectable Pancreatic Adenocarcinoma.

OBJECTIVES: Pancreatic ductal adenocarcinoma (PDA) is the third most common cause of cancer death in the United States. Most patients who undergo resection develop recurrence. Standard treatment confers a median overall survival (OS) of 24 months. Exposure to alternate regimens may prevent chemoresistance. This study evaluated multiagent perioperative therapy for potentially resectable PDA patients to improve OS. METHODS: A single center, phase 2, trial of patients with resectable or borderline resectable PDA. Patients received neoadjuvant therapy with induction chemotherapy (gemcitabine, docetaxel, capecitabine) for 3 cycles, chemoradiation (intensity-modulated radiation therapy with capecitabine and oxaliplatin) followed by surgery, and 2 months of adjuvant gemcitabine and oxaliplatin and 2 months of gemcitabine. The primary endpoint was OS. The secondary endpoint was recurrence-free survival (RFS). RESULTS: Thirty-two eligible patients were enrolled. Twenty-two patients underwent surgical resection. After a median follow-up of 56.8 months, mOS was 31.6 months (95% confidence interval [CI], 14.2-58.1) for all patients, 58.1 months (95% CI, 31.6 to NR) for those who completed surgery. The mRFS was 31.3 months (95% CI, 12.5 to NR). CONCLUSIONS: Perioperative therapy with GTX, chemoradiotherapy, and adjuvant GemOx/Gem resulted in promising survival of 58 months for patients who underwent resection and may represent another treatment option for PDA.

IgG and IgM Immunohistochemistry in Primary Biliary Cholangitis (PBC) and Autoimmune Hepatitis (AIH) Liver Explants.

OBJECTIVES: Primary biliary cholangitis (PBC) and autoimmune hepatitis (AIH) can be difficult to distinguish in end-stage liver disease. Previous studies have shown that immunoglobulin G (IgG) and immunoglobulin M (IgM) immunostaining can differentiate AIH from PBC in needle core biopsy specimens, and we seek to extend these data to cirrhotic liver explants, in which the histology of AIH or PBC may be indiscernible. METHODS: Clinical data were reviewed for 20 patients with PBC cirrhosis and 16 with AIH cirrhosis. Immunohistochemistry for IgM and IgG was performed on representative blocks of explanted livers. Three high-power fields with the highest concentration of IgG- and IgM-positive plasma cells were counted and compared. RESULTS: The average number of IgM-positive plasma cells was significantly higher in PBC explants (7.3) than in AIH (1.8) (P = .001). There was no significant difference in the average number of IgG-positive plasma cells in PBC (2.5) and AIH (2.8) (P = .8). The IgG/IgM ratio was more likely to be less than 1.0 in PBC (17/20, 85%) compared with AIH (7/16, 44%) (P = .01). CONCLUSIONS: Our study demonstrates that the absolute number of IgM plasma cells is greater in explants of cirrhotic PBC compared with AIH. These findings may be helpful in the evaluation of cryptogenic cirrhosis.

Patient navigation for hereditary colorectal cancer: Design of a randomized controlled trial to determine the effectiveness of pathways to genetic counseling.

BACKGROUND: Diagnosis of Lynch and other hereditary colorectal cancer (CRC) syndromes through germline genetic testing has important implications for treatment and risk-management, yet guideline-recommended genetic counseling referral and attendance is suboptimal. METHODS: Our team developed an adapted patient navigation program-Pathways to Genetic Counseling-to address multilevel barriers to genetic counseling referral and receipt. This paper describes the methods of a randomized controlled trial (RCT) testing Pathways to Genetic Counseling's effectiveness at increasing genetic counseling attendance in the University of Washington Medicine health system. We will identify CRC patients eligible for genetic counseling (diagnosed before age 50 or at any age with evidence of inherited mismatch repair deficiency) through a combination of structured electronic health record queries and manual chart review. Patients will be randomized 1:1 prior to consent and receive either care as usual (no contact) or be invited to participate in patient navigation. We will use chart review to compare rates of genetic counseling referral and attendance within six months of randomization, regardless of patients' engagement with navigation. We plan to identify and randomize 161 eligible CRC patients over a nine-month period beginning in late 2021. DISCUSSION: Our pragmatic RCT design will provide real-world data on the potential for patient navigation to address longstanding care gaps in preventive genomic medicine. If effective, we hope to pilot Pathways to Genetic Counseling in additional settings with a long-term goal of improving appropriate diagnosis of hereditary CRC syndromes and subsequent cascade screening of eligible family members.

Dedifferentiated Liposarcoma Presenting as Dysphagia and Weight Loss: Common Symptoms but an Uncommon Diagnosis.

A 76-year-old woman was referred for 6 months of progressively worsening dysphagia and unintentional weight loss. An esophagogastroduodenoscopy demonstrated an area of extrinsic compression in the lower esophagus measuring 7 cm in greatest dimension. Contrast-enhanced computed tomography revealed a solid homogeneous mass in the lower middle/posterior mediastinum, laterally displacing the esophagus. Endoscopic ultrasound-guided fine-needle biopsy showed a hypocellular infiltrate of pleomorphic cells in a loose collagenous matrix. By immunohistochemistry, neoplastic cells were negative for epithelial, vascular, neural, and melanocytic markers. Fluorescent in situ hybridization detected MDM2 amplification, compatible with a diagnosis of dedifferentiated liposarcoma.

Neutrophilic inflammation in gallbladder carcinoma correlates with patient survival: A case-control study.

Gallbladder carcinoma is an uncommon malignancy with an overall 5-year survival of less than 5%. Gallbladder carcinoma has been strongly linked with cholelithiasis and chronic inflammation. Case reports and series have described cholecystitis with acute (neutrophilic) inflammation in association with gallbladder carcinoma, although a clear relationship to patient outcome has not been established. Our series included 8 cases of gallbladder carcinoma with high tumor-associated neutrophils (>25 per high power field) that were associated with shorter patient survival (Cox regression coefficient 6.2, p = 0.004) than age- and stage-matched controls. High tumor-associated neutrophils were not associated with gallbladder rupture/perforation or increased bacterial load measured by 16S PCR. Neutrophilic inflammation with gallbladder carcinoma correlates to shorter survival, independent of patient age and stage of carcinoma. The findings suggest that the degree of neutrophilic inflammation may have prognostic significance in specimens from patients with gallbladder carcinoma after cholecystectomy. Further studies with larger case numbers are needed to confirm and generalize these findings.

Centrizonal hepatocyte dropout in allograft liver biopsies: a clinicopathological study.

AIMS: Centrizonal hepatocyte dropout has been described in diverse liver pathologies, including viral hepatitis, venous outflow obstruction, and allograft cellular rejection. However, its clinical significance remains uncertain. METHODS AND RESULTS: We designed a clinicopathological study of 206 allograft liver biopsies with centrizonal hepatocyte dropout. Centrizonal hepatocyte dropout was associated most frequently with cellular rejection (n = 62), asymptomatic/protocol biopsies (n = 56), immediate post-transplantation biopsies (n = 21), biliary obstruction (n = 14), and viral hepatitis (n = 13). The differential diagnosis is informed by timing post-transplantation, biliary imaging and laboratory test results. 'Cholestatic' and 'hepatocytic' laboratory patterns were associated with biliary obstruction and cellular rejection, respectively. A mixed pattern peaking after biopsy was observed in viral hepatitis cases. In the context of cellular rejection, dropout was not associated with the time interval to normalisation of serum alanine aminotransferase (ALT), but was associated with shorter transplant-free survival (hazard ratio 4, P = 0.01) than that of histological severity-matched controls. In time zero allograft biopsies, time to ALT normalisation was prolonged (median, 15 versus 11 days, P = 0.002) in allografts with centrizonal dropout, with no effect on retransplant-free survival. CONCLUSIONS: Centrizonal hepatocyte dropout has low clinicopathological diagnostic specificity. However, it correlates with adverse clinical outcomes in allograft cellular rejection and time zero biopsies.

Role of DNA Flow Cytometry in the Diagnosis of Malignancy in Bile Duct Biopsies Using Paraffin-Embedded Tissue.

OBJECTIVES: Histopathologic evaluation of bile biopsies for biliary strictures is frequently challenging and is affected by interobserver disagreement. Reliable ancillary tests that can help differentiate benign from malignant are not available. This study aimed to evaluate whether DNA content abnormalities detected by flow cytometry on formalin-fixed, paraffin-embedded (FFPE) tissue can help differentiate benign/reactive, dysplastic from malignant cell populations in bile duct biopsies. METHODS: We performed DNA flow cytometry on 30 FFPE bile duct biopsies in 5 well-defined diagnostic categories: (1) negative for dysplasia (NED), (2) low-grade dysplasia (LGD), (3) high-grade dysplasia (HGD), (4) carcinoma (CA), and (5) indefinite for dysplasia (IND). RESULTS: Abnormal DNA content was detected in 0 NED, 5 LGD (62.5%), 2 HGD (33.3%), 3 CA (60%), and 4 IND (80%) samples. As a diagnostic marker, the estimated sensitivity, specificity, positive predictive value, and negative predictive value were 63%, 100%, 100%, and 50%, respectively, for diagnosing HGD or CA. CONCLUSIONS: DNA flow cytometry analysis is a useful ancillary test for the interpretation of bile duct biopsies. DNA content abnormalities, when correlated with histologic findings, will not only help confirm the morphologic impression but also identify patients who are at a higher risk of developing malignancy.

Esophageal granular cell tumor and eosinophils: a multicenter experience.

BACKGROUND: Esophageal granular cell tumor (eGCT) is rare, and the recent literature suggests a link between eosinophilic esophagitis (EoE) and eGCT. The aim of our study was to determine if EoE or other disorders associated with eosinophilia are consistently associated with eGCT. METHODS: We retrospectively searched pathology databases of three academic institutions from 1999 to 2018 for eGCTs. The archived slides and medical records were reviewed. RESULTS: From 294,855 esophagogastroduodenoscopy procedures, 45 patients (17 males and 28 females) with eGCTs were identified. The patients (30-73 years in age, median 50) had eGCT 0.2-2.0 cm in size (average 0.71). Thirteen had a history of gastroesophageal reflux disease, 5 had Barrett esophagus/goblet cell metaplasia and 1 had EoE. Thirty-four eGCTs had intralesional eosinophils (14 with peak > 10 eosinophils/400x hpf); of these, 21 also had eosinophils in lamina propria (9 with peak > 10 eosinophils/hpf). eGCT with atypical features (including nuclear enlargement and prominent nucleoli) were more likely to have increased eosinophils in non-epithelial compartments than those without atypia. Pleomorphism and spindled cells were seen in 3 eGCT cases (mean peak intralesional eosinophils: 43 per hpf); 2 of these had goblet cell metaplasia. We found no association between EoE and eGCT, p = 0.5966, (95% C.I. 0.0276, 6.5389, Fisher's exact test). Instead, most patients had gastroesophageal reflux disease or Barrett esophagus. CONCLUSION: Eosinophilia, common in eGCT and adjacent stroma, likely drives atypical/reactive histologic features, but a pathogenic relationship between eosinophil rich inflammatory conditions and eGCT has not yet been established.

S100P as a marker for poor survival and advanced stage in gallbladder carcinoma.

AIMS: Gallbladder carcinomas usually present in advanced stages and has a dismal prognosis despite modern imaging techniques and aggressive surgical intervention. Identification of biologic markers for early diagnosis and improved therapeutic strategies is thus of paramount importance. S100P has been identified in a variety of malignant neoplasms of the gastrointestinal and pancreaticobiliary systems, but it is not yet known if S100P expression is associated with clinically-relevant characteristics of gall bladder carcinoma. The aims of the present study were: 1) to investigate the relationship between S100P expression and histological type, grade, tumor-node-metastasis stage, presence of vascular invasion, perineural invasion and necrosis; and 2) to evaluate for any S100P-defined difference in the risk for tumor recurrence or death. METHOD: Immunostains for S100P were performed on 4 tissue microarray blocks containing 91 cases of gall bladder carcinoma. RESULT: The intensity of S100P staining was significantly associated with pathological T stage 4 (p = 0. 0238). Staining intensity ≥3 in ≥25% tumor cells was associated with pathological T stage 4 (p = 0.0005). A higher S100P immunoreactivity score (IRS) was significantly associated with higher TNM stage (p = 0.0341). Age (p = 0.0485), presence of vascular invasion (p = 0.0359), pathological T stage (p = 0.0291) and TNM stage (p = 0.0153) were significantly associated with tumor recurrence. Intense S100P reactivity was associated with decreased overall survival [hazard ratio = 9.614; 95% confidence interval (CI), 1.873-49.338; p = 0.0067]. CONCLUSION: Our findings indicate that S100P over-expression is a potential prognostic marker for gall bladder carcinoma and is significantly associated with advanced tumor stage and poorer survival.

Metastases can occur in cirrhotic livers with patent portal veins.

OBJECTIVES: Metastases are common in non-cirrhotic livers but are considered unlikely in the setting of cirrhosis. However, the degree of fibrosis in cirrhosis may vary; thus metastases may still access the liver vasculature and present as a mass in cirrhotic livers. This possibility may affect pathologists' diagnostic algorithms when faced with a liver mass biopsy. METHODS: We hypothesized that metastases can occur in cirrhotic livers if fibrous remodeling is not severe or abnormal veno-arterial shunting exists to override an obstructed portal system. We searched departmental archives for cirrhotic livers with masses, categorizing fibrosis by Laennec staging: 4A = mild cirrhosis, 4B = moderate, 4 C = severe. RESULTS: Of 1453 cirrhotic livers with masses, 1429 were primary tumors and 24 were metastases (1.7 %). Of livers with metastases, most had 4A or 4B cirrhosis by Laennec staging (n = 17; 71 %). Eleven patients were evaluated by ultrasound Doppler; 2 of 5 with Laennec 4 C had reversal of portal vein flow, but all 4A & 4B patients had patent portal veins without reversed flow. Echocardiograms (13 patients) showed no ventricular or atrial septal defects or arteriovenous shunts. CONCLUSIONS: Metastases are uncommon in cirrhotic livers, accounting for 1.7 % of masses. Most involved livers had mild or moderate cirrhosis (Laennec 4A/4B) and patent portal veins; however, as some Laennec 4 C cases also contained metastases, obstructed portal access may not be enough to deter metastatic access.

Duodenal intraepithelial lymphocytosis in Helicobacter pylori gastritis: comparison before and after treatment.

Our aims were to assess performance of duodenal intraepithelial lymphocyte counting for diagnosis of Helicobacter pylori (H. pylori) gastritis, and effects of eradication therapy on intraepithelial lymphocytosis. Paired duodenal and gastric biopsies from subjects with a pathologic diagnosis of H. pylori gastritis were reviewed. Higher duodenal intraepithelial lymphocyte counts were observed in 40 subjects with H. pylori gastritis (26 ± 5 per villus) than 52 subjects negative for H. pylori (12 ± 2 per villus). After successful eradication therapy, duodenal lymphocytes were indistinguishable from H. pylori-negative subjects, whereas they remained elevated after failed eradication therapy. This study confirms previous reports of increased duodenal intraepithelial lymphocytes in patients with concurrent Helicobacter pylori gastritis. Intraepithelial lymphocyte counts of > 15 per villus or > 10 per 100 enterocytes were predictive of infection. Duodenal lymphocytosis decreases significantly after successful eradication therapy but remains elevated when treatment fails.

Interobserver agreement in pathologic evaluation of bile duct biopsies.

Intraductal biopsy is commonly used for preoperative evaluation of the etiology of biliary strictures. Interpretation of intraductal biopsies is frequently challenging. The diagnosis often suffers from interobserver disagreement, which has not been studied in the literature. We sought to assess interobserver concordance in the interpretation of intraductal biopsies. Eighty-five biopsies were retrieved, falling into five diagnostic categories: negative for dysplasia (NED), indefinite for dysplasia (IND), low-grade dysplasia (LGD), high-grade dysplasia (HGD), and carcinoma (CA). Eight gastrointestinal pathologists blindly reviewed all the slides. Agreement among pathologists was analyzed using Fleiss κ and weighted concordance coefficient S∗. A face-to-face consensus/training session was held to discuss the classification criteria, followed by a second round review. The overall interobserver agreement was fair in the first round review (κ = 0.39; S∗ = 0.56) and improved to moderate in the second round review (κ = 0.48; S∗ = 0.69). The agreement before and after consensus meeting was substantial to nearly perfect for CA (κ = 0.65, S∗ = 0.83; and κ = 0.80, S∗ = 0.91), fair for HGD (κ = 0.28, S∗ = 0.69; and κ = 0.40, S∗ = 0.63), and moderate for NED (κ = 0.47, S∗ = 0.50; and κ = 0.47, S∗ = 0.53). Agreement improved from fair to moderate for LGD (κ = 0.36, S∗ = 0.61; and κ = 0.49, S∗ = 0.71) and slight to fair for IND (κ = 0.16, S∗ = 0.51; and κ = 0.33, S∗ = 0.50). Compared with Hollande's fixed specimens, the agreement was higher in almost all diagnostic categories in formalin-fixed biopsies. Overall, interobserver concordance was improved after a consensus/training session. Interobserver reproducibility was high at the end of the diagnostic spectrum (CA) but fair to moderate for other diagnostic categories.

Operational Impacts of the Coronavirus Disease 2019 (COVID-19) Pandemic and Early Recovery Trends: University of Washington Anatomic Pathology Experience.

CONTEXT.­: The coronavirus disease 2019 pandemic, caused by the novel coronavirus severe acute respiratory syndrome coronavirus 2, has resulted in worldwide disruption to the delivery of patient care. The Seattle, Washington metropolitan area was one of the first in the United States affected by the pandemic. As a result, the anatomic pathology services at the University of Washington experienced significant changes in operational volumes early in the pandemic. OBJECTIVE.­: To assess the impact of coronavirus disease 2019 and both state and institutional policies implemented to mitigate viral transmission (including institutional policies on nonurgent procedures) on anatomic pathology volumes. DESIGN.­: Accessioned specimens from January to June 2020 were evaluated as coronavirus disease 2019 and institutional policies changed. The data were considered in these contexts: subspecialty, billable Current Procedural Terminology codes, and intraoperative consultation. Comparable data were retrieved from 2019 as a historical control. RESULTS.­: There was a significant reduction in overall accessioned volume (up to 79%) from prepandemic levels during bans on nonurgent procedures when compared with 2020 pre-coronavirus disease 2019 volumes and historical controls. The gastrointestinal and dermatopathology services were most impacted, and breast and combined head and neck/pulmonary services were least impacted. Current Procedural Terminology code 88305, for smaller/biopsy specimens, had a 63% reduction during nonurgent procedure bans. After all bans on procedures were lifted, the overall volume plateaued at 89% of prepandemic levels. CONCLUSIONS.­: A significant decrease in specimen volume was most strongly associated with bans on nonurgent procedures. Although all departmental areas had a decrease in volume, the extent of change varied across subspecialty and specimen types. Even with removal of all bans, service volume did not reach prepandemic levels.

Helicobacter pylori Antigen But Not the Organism Is Occasionally Present Within Germinal Centers: Implications for Patient Management and Biology.

Helicobacter pylori infection is present in two thirds of the world's population and induces a myriad of human diseases, ranging from gastritis to gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma. Detection is critical for treatment and may require immunohistochemical (IHC) staining when organisms are not visible on hematoxylin and eosin. We have encountered cases in which IHC for Helicobacter pylori failed to demonstrate curvilinear or coccoid organisms, but did show a reticular pattern of immunoreactivity involving the underlying germinal centers. We performed a systematic retrospective evaluation of the frequency of H. pylori germinal center immunoreactivity over a 54-month period through evaluation of 367 gastric specimens. H. pylori germinal center immunoreactivity was observed in 5% of cases with germinal centers. Nine of 11 (81%) patients with H. pylori germinal center immunoreactivity had concurrent or recent H. pylori infection, in comparison to 36% of patients with germinal centers present but no immunoreactivity (n=9 of 25 patients, P=0.03). None of the patients with germinal center immunoreactivity developed mucosa-associated lymphoid tissue lymphoma. In situ hybridization for H. pylori performed on 3 cases with positive germinal center IHC was negative for H. pylori nucleic acids within those germinal centers, demonstrating that only the antigen is present. This work demonstrates that H. pylori antigen, but not viable organisms, is present in germinal centers in 5% of gastric specimens, and is associated with recent or concurrent H. pylori infection. We advocate for reporting of all H. pylori germinal center immunoreactivity with a recommendation for ancillary H. pylori testing.

Serology Is More Sensitive Than Urea Breath Test or Stool Antigen for the Initial Diagnosis of Helicobacter pylori Gastritis When Compared With Histopathology.

OBJECTIVES: To assess the concordance and performance characteristics of Helicobacter pylori laboratory tests compared with histopathology and to propose algorithms for the diagnosis of H pylori that minimize diagnostic error. METHODS: H pylori diagnostics were reviewed from a 12-year period within a health system (2,560 cases). Analyses were performed to adjust diagnostic performance based on treatment and consensus histopathologic diagnoses among pathologists. Markers of access to care, including test cancellation frequency and turnaround time, were assessed. Costs and performance of candidate noninvasive testing algorithms were modeled as a function of disease prevalence. RESULTS: Serum H pylori IgG demonstrated a higher sensitivity (0.94) than urea breath and stool antigen tests (0.64 and 0.61, respectively). Evidence of an advantage in access to care for serology included a lower cancellation rate. Interobserver variability was higher (κ = 0.34) among pathologists for cases with a discordant laboratory test than concordant cases (κ = 0.56). A model testing algorithm utilizing serology for first-time diagnoses minimizes diagnostic error. CONCLUSIONS: Although H pylori serology has modestly lower specificity than other noninvasive tests, the superior sensitivity and negative predictive value in our population support its use as a noninvasive test to rule out H pylori infection. Reflexive testing with positive serology followed by either stool antigen or urea breath test may optimize diagnostic accuracy in low-prevalence populations.