Plasma Volume Is an Important Determinant in Assessing Metabolic and Iron Biomarkers in Young Women

Abstract Objectives Plasma volume (PV) variations among individuals can affect the concentration of blood biomarkers but this is not often evaluated in assessing nutritional status. We aimed to assess the association between estimated PV, metabolic and iron biomarkers in young obese and normal weight women. Methods Healthy women aged 18–30 y were recruited for the study (n = 47: 25 obese and 22 normal weight). Fasting venous blood samples were obtained to measure serum lipids, comprehensive metabolic panel, iron biomarkers (serum iron, total iron binding capacity, transferrin saturation (%TS), hemoglobin, ferritin and, hepcidin). PV was estimated using Kaplan-Hakim formula: PV = (1-hematocrit) × [a + (b × weight in kg)] where adjustment factors were a = 864, and b = 47.9. Associations between PV and other biomarkers were assessed using Pearson's correlation. Results As expected, PV was higher in obese (3482 (545) mL) than normal weight women (2268 (250) mL). When all subjects were combined PV was negatively correlated with HDL (r = −0.49, P = 0.001), creatinine (r = −0.48, P = 0.001), sodium (r = −0.31, P = 0.034), calcium (r = −0.30, P = 0.044), albumin (r = −0.46, P = 0.001), serum iron (r = −0.34, P = 0.022), and %TS (r = −0.31, P = 0.036) but positively correlated with triglycerides (r = 0.40, P = 0.005), cholesterol/HDLC ratio(r = 0.55, P < 0.001). In normal weight women, PV was not correlated with any of these biomarkers. However, in obese women, there was a strong correlation of PV with creatinine (r = −0.61, P = 0.001), calcium (r = −0.50, P = 0.012), and albumin (r = −0.43, P = 0.030). Conclusions Our results suggest that differences in PV may account for some variations in serum lipids, creatinine, sodium, calcium, albumin, and iron biomarker concentrations in women. This implies that different cutoffs may be needed for defining deficiencies in obesity after correcting for plasma volume. Funding Sources Doris A. Adams Endowed Chair funds at Iowa State University.