A wide variety of factors impact Hb levels in the body and total hemoglobin measurement. Depending on the techniques used, Hb measurement can vary significantly in the same patient. Clinicians should be aware of these factors as HB testing plays an important role in treating anemia and other red blood cell disorders. Factors impacting Hb measurement include
- The device used – CO-Oximeter or point-of-care
- Blood source – venous or arterial. Studies have found that arterial Hb measurements tend to be less than Hb measurements from venous blood. The percentage of plasma concentration can be higher in arterial blood leading to lower Hb concentrations
- Site of blood draw – large differences have been reported from capillary blood samples from left and right hands of the same subject and from different fingers of the same person
- Blood-mixing errors can have an additional variability impact on Hb measurement
- Time – Hb measurement can differ over time, on different occasions and on different days
- Position of the body – upright, standing or sitting, moving from seated to standing position
Blood draw techniques also affect Hb measurement. If the patient’s finger is squeezed during the fingertip capillary draw or if the site is wet from alcohol solution when punctured, the sample will get diluted, lowering the concentration of red blood cells in it. Also, microcuvettes that contain air result in false low Hb concentration readings.
On the other hand, false high hb concentration readings can occur if the blood samples clot before the cuvettes filled or if the microcuvettes are not completely filled due to insufficient blood flow from a shallow stick.
With point-of-care testing is being widely adopted for its convenience and fast results, devices such as Alere’s HemoPoint® H2 System have gained popularity. Comprising a dedicated meter and individual, single-use Alere HemoPoint® H2 Microcuvettes filled with reagents, this system can provide a quantitative determination of hemoglobin in capillary, venous, or arterial whole blood adults, infants, and children in a professional point-of-care setting.