Elevated leukocyte count as a harbinger of systemic inflammation, disease progression, and poor prognosis: a review

Total leukocyte count increases significantly in response to infection, trauma, inflammation, and certain diseases. Factors affecting leukocyte count in healthy adults include sex, hormonal milieu, genetic inheritance, stress level, diet, nutrition, and lifestyle (e.g. tobacco-induced inflammatory changes, chronic psychological stress, etc.). To date, numerous studies have reported that high but normal leukocyte counts at baseline predict increased cardiovascular and noncardiovascular mortality in older adults. Recent findings suggest that elevated leukocyte count within the normal range, but especially neutrophil and monocyte counts, may be a harbinger of increased systemic inflammation and subclinical disease. Moreover, elderly people who tend to have high but normal leukocyte counts are at greater risk of cancer, cardiovascular disease, type 2 diabetes, some other age-related conditions, and they also have increased all-cause mortality. These results indicate that strong and reliable inflammatory markers, such as leukocyte count, may reflect the rate of ageing and therefore can predict long-term survival in the elderly. Remarkably, leukocyte count correlates positively with genuine markers of systemic inflammation like C-reactive protein and interleukin 6. Interestingly, some authors conclude that leukocyte counts have a stronger prognostic ability with regard to total and cardiovascular mortality than total cholesterol or low-density lipoproteins. The fact that these inflammatory markers are clinically useful predictors of long-term survival in the elderly is quite remarkable as these blood parameters are included in routine medical check-ups. Therefore, they can be used as simple and reliable morphological indicators of chronic systemic inflammation, disease progression, and poor prognosis, especially among individuals who are likely to develop age-related conditions. Nevertheless, the pathomechanism that links elevated but normal leukocyte counts to increased mortality remains poorly understood. This review summarises the most important findings on the links between leukocyte count, chronic systemic inflammation, and health outcomes in older adults. (Folia Morphol 2018; 77, 2: 171-178).