Noninvasive blood cell measurements by imaging of the microcirculation.

A novel approach to noninvasive clinical laboratory testing1 has formed the basis for an intense current developmental effort aimed at routine hematology.2 It uses in vivo image capture plus reflectance spectroscopy to quantify certain parameters of the conventional CBC count: viz, WBCs, RBCs, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin content (MCHC), and capillary and central venous hematocrit measurements. Images of many different vessels of the microcirculation are fed into a computerized image analysis system capable of identifying numerous individual cells simultaneously and analyzing them in real time. An instrument capable of producing these components of the CBC without extracting blood from the body could have substantial usefulness in current medical practice, including immediate availability of information, avoidance of phlebotomy and blood loss, accessibility of data from patients with compromised vascular status, and cost avoidance and cost containment owing to improved patient outcomes in critical care settings. This article introduces a new development based on noninvasive visualization of the microcirculation that produces useful clinical information, which currently requires phlebotomy and conventional laboratory testing. Blood flowing in small vessels and capillaries has been visualized in humans and other animals by numerous experimental techniques, many of which require invasive procedures and cumbersome instrumentation. Ophthalmologists, using slit lamps, have long observed widely separated but essentially featureless individual RBCs in the uveal vein, which drains the aqueous humor. But with advanced electrooptical systems, superior images of circulating cells and measurements of them can be made from this or other visually accessible vessels. In vivo morphometry and reflectance spectroscopy of these images can directly quantify parameters of the conventional CBC, viz, MCV, MCH, MCHC, and hematocrit. From these values, using the familiar equations for the computation of RBC indices, the other conventional measures that describe the RBC population of the individual can be computed. WBCs and platelets can be identified by reflectance spectroscopy in the UV portion of the spectrum combined with classification based on their dimensions.