Serum insulin-like growth factor binding protein-3 responds differently to trauma in men and women

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Abstract
Insulin-like growth factor-1 (IGF-1) has been studied as a marker of nutrition in critical illness, but there is little research on IGF-binding protein-3, which regulates the bioactivity of IGF-1. The objectives of the present study were to measure serum IGF-binding protein-3 concentrations in trauma patients and to determine whether factors such as age, gender, and severity of injury should be considered when evaluating serum IGF-binding protein-3 concentrations as a marker of nutritional or clinical status. Prospective, randomized, descriptive study. Emergency room of a university hospital. One hundred eight trauma patients. None. In this diverse group of patients, Injury Severity Score ranged from 1 to 45 (11.5 +/- 10.3 [SD]), age ranged from 18 to 77 yrs (35 +/- 15.3), and 68% were male. A venous blood sample was collected at the time of admission into the study and was analyzed for serum IGF-binding protein-3 concentration (by radioimmunoassay), serum osmolality, IGF-1 concentration, and C-reactive protein concentration. Relationships between variables were tested using Pearson's correlation coefficients and multiple regression analysis. Age, Injury Severity Score, serum osmolality, time since injury, and gender were not significant predictors of serum IGF-binding protein-3 concentrations when all patients were analyzed together. However, when men and women were analyzed separately, notable gender differences were observed. In women, serum IGF-binding protein-3 concentrations were increased with increasing severity of injury (beta = 0.52, R2 = .33, p < .01). In men, the opposite relationship was observed (beta = -0.29, R2 = .17, p < .01). Other predictors in the model (age, serum osmolality, and time since injury) were not significant. Variability in IGF-binding protein-3 concentration could not be explained by differences in body mass index or acute-phase response (serum C-reactive protein). Serum IGF-1 concentrations changed coordinately with IGF-binding protein-3 concentrations in females and males (r = .62, p < .001 and r = .54, p < .001, respectively). IGF-binding protein-3 concentration at the time of admission into the study could not predict mortality, but this value was correlated with length of hospitalization in women (r = .37, p < .05). Determination of the specificity and sensitivity of IGF-binding protein-3 as an index of nutrition or anabolism requires knowledge of its relationship to nonnutritional factors. These factors are most discernible before the confounding effects of treatments, absence of feeding, and complications. The present study demonstrated that gender and severity of injury must be considered when interpreting serum IGF-binding protein-3 concentrations in trauma patients. In a much wider context, the present findings suggest that the study of the metabolic response to stress requires separate analyses, based on gender.

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