Fecal dimeric M2-pyruvate kinase (tumor M2-PK) in the differential diagnosis of functional and organic bowel disorders

Abstract

Fecal inflammatory markers have been shown to be useful as noninvasive screening tools to differentiate patients with functional from organic bowel pathology. Of these markers calprotectin has been the most intensively studied. More recently, the dimeric isoform of M2-pyruvate kinase (tumor M2-PK) has been suggested as a marker of gastrointestinal inflammation. The aim of this study was to investigate fecal tumor M2-PK in the differentiation of functional from organic bowel disease. Fecal calprotectin and tumor M2-PK were measured in 94 controls and 105 gastroenterology outpatients with a possible diagnosis of organic bowel disease. The diagnosis was made by clinical, endoscopic, and radiological criteria. Organic bowel disease was diagnosed in 14 patients (13%). Median calprotectin and tumor M2-PK concentrations were 24.5 microg/g and 1 U/mL in controls, 23 microg/g and 1 U/mL in functional, and 227.5 microg/g and 12.6 U/mL in organic bowel disease. Sensitivity, specificity, and positive and negative likelihood ratios for diagnosis of organic bowel disease were 93%, 92%, 11.6, and 0.07 for calprotectin and 67%, 88% 5.6, and 0.18 for tumor M2-PK, respectively. Calprotectin in combination with tumor M2-PK gave a sensitivity of 64%, specificity of 98%, and likelihood ratios of 32 and 0.03. Elevated calprotectin or tumor M2-PK decreased specificity to 87%, but increased sensitivity to 100%. Tumor M2-PK is able to differentiate organic from functional bowel disease but has a lower sensitivity, specificity, and predictive value than calprotectin. Further studies are required, alone or in combination with other markers, before its usefulness in this setting can be recommended.