Hemoglobin, found in red blood cells (RBCs), transports oxygen from the lungs to the rest of the body for use in oxidative metabolism. Anemia (<11 g/dl for pregnant women) results from a decrease in the normal number of RBCs or less than the normal quantity of hemoglobin per RBC. Anemia during pregnancy is associated with increased risk of stillbirth, preterm delivery, low birth weight, delayed cognitive development and increased maternal mortality, especially in the case of hemorrhage.
Mechanism of Action
There are several qualitative and quantitative methods for determining Hb concentration. Qualitative methods include clinical examination and referencing the color of a drop of blood on filter paper to a standardized color comparison chart. Quantitative techniques typically require a blood sample and determine Hb concentration using specific gravity (as in the copper sulfate method), visual color comparison (as in the grey wedge), relative volume (as in the centrifuge method), or light absorption (as in HemoCue). More recently, non-invasive quantative methods have been developed which measure the transmission of light through the patient’s finger, similar to pulse oximetry.
Current Use in High-Resource Settings
Blood test samples are typically taken from the patient to centralized laboratories where Hb measurement is part of a larger battery of tests, often done on a single, autoloading, automated machine. One such hematology analyzer is the Abbott CELL-DYN 4000 which can measure 26 different parameters including Hb on 110 samples per hour. The international standard for Hb measurement is the cyanmethemoglobin spectrophotometry, which is best suited to centralized labs.
Application in Low-Resource Settings
Where patients may not be able to return for test results, point of care tests are favorable. Clinical exams and filter paper are the least sensitive and specific, but the most widely available. Copper sulfate based tests can be used where power is not available, and is somewhat less subjective than color matching methods. In all of the above cases, the more severe the anemia, the more easily it can be detected. If power is available, a larger range of tests can be performed, including hematocrit by centrifuge. This method has the advantage of processing multiple samples at once, in a higher volume setting. While more costly, hand-held automated devices like Hemocue offer high speed, high accuracy quantitative screening, and are often well suited to surveys.
Related Technologies in Development
ToucHb, NBN 200 Nonoinvasive Hemoglobin, Anemicam, Hand Powered Centrifuge