Benchtop NMR Relaxometry in Clinical Diagnostics: Whole Human Blood

Purpose: Benchtop NMR relaxometry is a promising technology for metabolic heath screening and assessment. Unlike spectrometry and imaging, NMR relaxometry uses compact and inexpensive devices, making it practical for clinical laboratories and point-of-care settings. In previous work, we reported that the water transverse relaxation time (T2) of human blood plasma is a sensitive and specific marker for early insulin resistance syndrome. Here, we investigated whether whole human blood could be analyzed directly, thus avoiding the centrifugation step and saving time and expense. During sample equilibration, anticoagulated whole blood sediments spontaneously inside the NMR tube, creating a cell pellet and a plasma supernatant. We exploited this phenomenon and designed experiments to measure the T2 values of the pellet and supernatant simultaneously. The goal of this study was to quantify the association of whole blood T2 values with over 200 established blood biomarkers in order to assess information content of the T2 data. Methods: We recruited 45 asymptomatic, non-diabetic human volunteers through an IRB-approved protocol. Blood samples were collected after an overnight fast, and NMR relaxation times were measured using a Bruker Minispec mq20 and a modified Carr-Purcell-Meiboom-Gill pulse scheme. The exponential decay curves were analyzed using a discrete inverse Laplace transform algorithm, as implemented in XpFIT (Alango, Ltd.), to extract T2 values. In addition, diagnostic testing was performed on each blood sample, mostly by Quest Diagnostics, Inc. and Atherotech, Inc. Results: The settled blood gives two distinct T2 values corresponding to supernatant (T2S) and cell pellet (T2P). Surprisingly, supernatant T2S correlates with red blood cell and hemoglobin markers, even though it lacks both red blood cell and hemoglobin after sedimentation. Therefore, we hypothesized that the paramagnetic deoxyhemoglobin from the cell pellet exerts a long-range influence on the plasma supernatant. This hypothesis was tested by a simulated hematocrit experiment that varied the height of the blood cell pellet, and a gadolinium experiment that altered the relaxation of samples that were physically separated. The cell pellet T2P correlates with insulin and lipid biomarkers from the blood. Conclusions: The results demonstrate that whole blood T2 values report on insulin resistance status, as well as hematocrit and hemoglobin levels.