Determination of IGF-I, IGF-II, IGFBP-2, and IGFBP-3 levels in serum and plasma: comparisons using the Bland–Altman method

The measurement of circulating insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) have significant implications in the risk assessment of various diseases (e.g. cancer) and growth abnormalities. It is often assumed that values measured in serum and plasma are interchangeable. This study challenges this assumption by comparing determinants using the Bland-Altman method. Blood was obtained from 47 healthy volunteers (age 21-72 years) in serum, heparin plasma and EDTA plasma, and IGF-I, IGF-II, IGFBP-2, and IGFBP-3 measured, and results compared. Mean values for IGF-I, IGF-II, IGFBP-2 and IGFBP-3 determined in all three media were generally comparable; correlations were generally strong and significant (P<0.001). However, the Bland-Altman plots revealed significant lack of agreement for many analytes measured in EDTA plasma compared with serum and heparin plasma. Additionally, the ranges of the limits of agreement were consistently greater for EDTA plasma compared with the other two methods. These findings emphasize the need to standardize methods of collecting blood samples in future epidemiological studies and trials.     

Brevity of haptic force perturbations induces heightened adaptive sensitivity

We have exposed human participants to both full-movement and pulsatile viscous force perturbations to study the effect of force duration on the incremental transformation of sensation into adaptation. Traditional views of movement biomechanics could suggest that pulsatile forces would largely be attenuated as stiffness and viscosity act as a natural low-pass filter. Sensory transduction, however, tends to react to changes in stimuli and therefore could underlie heightened sensitivity to briefer, pulsatile forces. Here, participants adapted within perturbation duration conditions in a manner proportionate to sensed force and positional errors. Across perturbation conditions, we found participants had greater adaptive sensitivity when experiencing pulsatile forces rather than full-movement forces. In a follow-up experiment, we employed error-clamped, force channel trials to determine changes in predictive force generation. We found that while participants learned to closely compensate for the amplitude and breadth of full-movement forces, they exhibited a persistent mismatch in amplitude and breadth between adapted motor output and experienced pulsatile forces. This mismatch could generate higher salience of error signals that contribute to heightened sensitivity to pulsatile forces.