Estimates of blood plasma water content using portable NMR relaxometry

Although blood plasma water content (PWC) is a relevant metric for many medical diagnostic procedures, the routine clinical measurement of PWC has remained elusive. Portable nuclear magnetic resonance (NMR) offers one way to nondestructively and quickly measure PWC. Contrived pseudoplasma samples that mimic blood plasma while also allowing rigorous control over water content are used to demonstrate the role of NMR in this work. Calibration curves relating measured NMR relaxation time constants (T ₂ and T ₁) to gravimetric PWC values for a set of human lyophilized plasma samples are used to predict the PWC in porcine and model human blood plasma from respective NMR T ₂ and T ₁ values. It is shown that the T ₂ and T ₁ decay constants measured with low field NMR relaxometry correlate with the PWC values for pseudoplasma and human lyophilized plasma samples. Statistical testing of the NMR-PWC correlation model demonstrated a prediction accuracy exceeding 98%. The PWC obtained in this way was used to correct sodium cation concentrations reported from direct ion-selective electrode tests. The accuracy of PWC determination with NMR is comparable to that of the gravimetric method that requires sample lyophilization. The rapid turnaround time, non-destructive nature, and portable footprint of the NMR-PWC measurement makes rapid, point-of-care clinical electrolyte estimates possible.