Common CBC Findings in H. Pylori Infection
The most common CBC finding in H. pylori infection is microcytic anemia (low hemoglobin with low MCV) due to iron deficiency, though some patients may also demonstrate elevated white blood cell and platelet counts. 1
Anemia and Red Blood Cell Parameters
Iron deficiency anemia is the hallmark CBC abnormality, presenting as decreased hemoglobin (<12 g/dL in females, <13 g/dL in men) with microcytic indices. 1
The prevalence of anemia among H. pylori-infected dyspeptic patients reaches 25.8%, significantly higher than the 15.3% seen in H. pylori-negative patients. 2
H. pylori causes iron deficiency through multiple mechanisms: atrophic gastritis with hypochlorhydria decreases iron absorption, chronic gastric blood loss depletes iron stores, and the bacteria may directly compete for dietary iron. 1
Treatment of H. pylori infection alongside iron replacement produces superior hemoglobin improvement compared to iron replacement alone—a mean difference of 2.2 g/dL greater improvement (95% CI, 1.3-3 g/dL). 1
Ferritin levels improve by an additional 23.2 ng/mL (95% CI, 12.2-34.3 ng/mL) when H. pylori is eradicated alongside iron supplementation. 1
White Blood Cell Findings
WBC count is independently and positively correlated with H. pylori infection, with infected patients demonstrating significantly higher WBC counts than uninfected controls. 3
The prevalence of H. pylori infection increases progressively across WBC quartiles, from 38.89% in the lowest quartile to 54.67% in the highest quartile. 3
The relationship between H. pylori bacterial load (measured by DPM values) and WBC count is non-linear, with distinct immunological responses at different infection stages: DPM <40 shows no significant effect, DPM 40-155 shows positive correlation (β=0.006, p=0.047), and DPM >155 shows negative correlation (β=-0.007, p=0.004). 3
In chronic long-term or past H. pylori infection, WBC levels gradually decrease compared to acute infection, suggesting immune system adaptation over time. 4
CD4+ T cell levels follow a similar pattern to total WBC, decreasing in past and chronic infections compared to uninfected controls. 4
Platelet Findings
Platelet counts are significantly elevated in H. pylori-positive patients compared to H. pylori-negative patients, with a positive correlation between bacterial load (DPM values) and platelet count (r=0.082, p=0.017). 3
This thrombocytosis likely represents a reactive inflammatory response to chronic infection rather than a primary hematologic disorder. 3
Clinical Implications and Pitfalls
In patients with unexplained iron deficiency anemia after negative bidirectional endoscopy, noninvasive H. pylori testing should be performed, followed by eradication therapy if positive. 1
Among children with refractory iron deficiency anemia (not responding to 3 months of iron therapy at 6 mg/kg/day), H. pylori infection is present in 48% of cases. 5
Do not rely on CBC findings alone to diagnose H. pylori—the sensitivity and specificity are insufficient. Use validated diagnostic tests such as urea breath test or monoclonal stool antigen test. 6
Avoid using rapid in-office serological tests for H. pylori diagnosis, as their accuracy averages only 78% and they cannot distinguish active infection from past exposure. 6
When evaluating anemia in H. pylori-infected patients, consider that the peripheral blood smear may show microcytic hypochromic red blood cells consistent with iron deficiency, but this finding is not specific to H. pylori. 2
Risk factors for severe anemia in H. pylori-infected patients include younger age at presentation and longer duration of infection, with patients presenting after age 4 years having significantly higher infection rates. 5