Proposal of blood-collecting needle approach to semi-invasive method

Many diabetic patients carry a portable self-monitoring of blood glucose (SMBG)-analyzer in order to collect their own blood and examine their glucose levels; this allows them to determine such factors as insulin dose, diet and exercise to stay healthy. However, the test causes physical and mental stress for the subjects. The authors aim to develop a semi-invasive blood-collecting needle which does not need a power source for the pump mechanism. In this study, we fabricated a capillary action needle that can collect the blood sample automatically. A blood-collecting needle was fabricated from 25 gage sized medical needle (diameter of 0.5 mm, stainless steel) by cutting process, and it had a half-opened crevice in the tip. In order to evaluate the physical characteristics of the blood-collecting needle, the relationship between the size and suction time and/or suction volume were measured using an isotonic sodium chloride solution, whole rabbit blood, and whole human blood with anticoagulant. Next, in order to evaluate the degree of invasion, the diameters of erythema in auricles of rabbits were observed for 2 days using a CCD camera-type microscope. The mean suction time of the isotonic sodium chloride solution and the whole rabbit blood were 1.5 s (n = 10) and 9.0 s (n = 5), respectively. Selection of a suitable size of the blood-collecting needle enabled the collection of 0.1 microL of whole human blood in 10 s. Moreover, it was shown, by comparing the observed diameter of the erythema, that the invasiveness of the blood-collecting needle was smaller than for commercial needles of the equal diameter. It became clear that this fulfils the fundamental functions of a semi-invasive blood-collecting needle.