The Role of Bedside Ultrasound in Nutritional Monitoring: An Observational Study on the Correlation Between Quadriceps Muscle Layer Thickness and Prealbumin in ICU Patients

Background: Malnutrition is a frequent complication in critically ill patients and is associated with adverse outcomes. Early and accurate assessment of nutritional status is essential but remains challenging in the ICU setting. Prealbumin is commonly used as a biochemical marker, while muscle ultrasound offers a non-invasive, bedside alternative for evaluating muscle mass and function. Objective: To evaluate the correlation between serum prealbumin levels and sonographic measurements of the quadriceps muscle in critically ill patients, and to determine their combined utility in identifying nutritional risk. Methods: A prospective, longitudinal, and analytical study was conducted over seven months in the ICU of a tertiary care hospital in Mexico. Fifty-six patients were included. Serum prealbumin levels and quadriceps muscle ultrasound measurements—anteroposterior (AP) and laterolateral (LL) diameters, cross-sectional area (CSA), and the Heckmatt scale—were obtained on admission (day 0) and on day 5 of ICU stay. Nutritional intake was documented, and muscle wasting was estimated as the percentage change in LL diameter. Data were analyzed using correlation tests, multiple linear regression, Cox regression, and ROC curve analysis. Results: Prealbumin levels decreased significantly by day 5 (Δ = -6.56 ± 5.5 mg/dL, p < 0.0001). At admission, LL and AP diameters showed weak to moderate correlations with prealbumin (r = 0.380 and r = 0.336, respectively), while CSA showed a modest correlation (r = 0.271, p = 0.043). On day 5, prealbumin correlated moderately with LL diameter, CSA, and percentage of muscle wasting. A strong correlation was observed between Δprealbumin and Δ LL diameter (r = 0.631, p < 0.0001). Multiple regression identified muscle wasting as the only significant predictor of prealbumin levels at day 5. ROC analysis revealed that AP and LL diameters at admission significantly predicted early nutritional compromise. Conclusions: Sonographic evaluation of the quadriceps muscle correlates with serum prealbumin levels in critically ill patients and provides a feasible, non-invasive method for early nutritional assessment. Combined use of both tools may improve the detection of malnutrition, allowing timely intervention and potentially enhancing clinical outcomes.