RESUMEN
Background: Hematin is a state in which hemoglobin, as petechiae, is discolored to a brown coffee color by gastric hydrochloric acid. Given the nature of hematin, a close relationship between hematin and acidity has been suggested, but has not been confirmed. We investigated the clinical significance of endoscopic finding of hematin with respect to gastric acidity. Methods: A total of 501 patients were assessed for both hematin and fasting gastric juice pH by endoscopy. Endpoints were as follows: 1) the relationship between the presence of hematin and the fasting gastric juice pH; and 2) the diagnostic performance of endoscopic hematin. In addition, we performed a supplementary in vitro study to clarify the relationship between hematin formation and various acid pH levels. Results: The prevalence of hematin was 31.1% (142/206), 4.6% (5/109) and 45.2% (84/186) in the H. pylori-uninfected, -infected and -eradicated groups, respectively. The mean pH of fasting gastric juice in the hematin-positive cases was significantly lower than the hematin-negative cases (mean pH 1.2, 95% confidence interval [CI] 1.1-1.3 vs. 2.7 95%CI 2.5-3.0; P<0.001). The sensitivity, specificity, positive predictive value and negative predictive value of hematin for predicting strong acidic condition (pH 1 or 2 for fasting gastric juice) were 36.0%, 98.1%, 98.7% and 29.3%, respectively. Interobserver agreement was categorized as "excellent" (k=0.88). Supplementary in vitro results showed that hematin formation was only observed at a pH=1. Conclusion: Endoscopic finding of hematin represent strong gastric acidity.