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The incidence of NHL has increased dramatically since at least the 1950s, and during this timeframe there has been a major increase in the use of blood transfusions, invasive surgical procedures and anesthesia, all of which can impact immune function. We evaluated these factors with NHL risk in a population-based study of 759 cases and 589 frequency-matched controls. Risk factor data were collected during in-person interviews. Unconditional logistic regression was used to estimate ORs and 95% CIs, adjusted for the matching factors. History of transfusion was associated with a 26% higher risk of NHL (95% CI 0.91–1.73), and the elevated risk was specific to transfusions first given 5–29 years before the reference date (OR = 1.69; 95% CI 1.08–2.62) and transfusions given for a medical condition (OR = 2.09; 95% CI 1.03–4.26). The total number of surgeries and dental procedures (OR = 1.53 for 26+ surgeries compared to 0–6; 95% CI 1.02–2.29) and to a lesser extent the total number of exposures to general or local/regional anesthesia (OR = 1.35 for 24+ times compared to 0–6; 95% CI 0.91–2.02) were positively associated with risk of NHL. Inclusion of transfusion and surgery or transfusion and anesthesia in the same model did not attenuate these associations. All results were broadly consistent for both DLBCL and follicular subtypes. Blood transfusions were associated with NHL risk, but appear to be a marker for underlying medical conditions. Multiple surgical procedures and/or repeated administration of anesthesia have not been previously reported to be associated with risk of NHL and these exposures warrant further evaluation. Published 2008 Wiley-Liss, Inc.