Developments in dried micro sampling
The use of dried blood spot analysis was already described in 1913 by Bang (Bang I; ein Verfahren zur Mikrobestimmung von Blutbestandteilen: Biochem. Ztschr. 49: 19-39:1913) in the estimation of blood glucose concentration. Around 1930 the use on venous blood for clinical measurements was common and because the equipment at that time was not sophisticated as it is today and whole blood a very difficult matrix is for clinical measurements, it was decided to separate the blood cells from the serum by centrifugation and to perform the clinical measurements in the serum which was a much easier matrix. Until now most clinical measurements are performed in the serum or plasma fraction and many reference values of clinical parameters are derived from these measurements.
The most prominent use of dried blood spots dates to the early sixties when Dr Robert Guthrie used dried blood spot specimens to measure phenylalanine in newborns for the detection of phenylketonuria (Guthrie and Susi 1963). This technique has been further developed to also perform quantitative determinations but encountered objections such as the influence of the hematocrit value and homogeneity of the sample.
Around 2015 Neoteryx introduced the Volumetric Absorptive Micro Sampling (Mitra tip), apart from the progress in user-friendliness the problems with hematocrit value and homogeneity were also largely solved.
The latest developments focus on the combination of a capillary where an accurate blood volume can be applied and a paper carrier. In combination with processing the total bloodspot, the accuracy and precision of this technique is comparable to pipetting blood with a positive displacement pipet. Another important aspect is that the user-friendliness for the customer who must collect the blood has strongly improved compared with the early blood spot method.
Soon a micro sampler is expected that can make a high-quality plasma spot from a capillary blood collection. A major advantage of such a system is that determinations that must be performed in plasma can also be done with micro sampling and that the plasma reference values can be used directly. The circle is then complete and dried micro sampling can then be applied on a larger scale.