Manual of basic techniques for a health laboratory - libdoc.who.int

9. Haematology 281Fig. 9.28 Micro scale for estimating the erythrocyte volume fractionFig. 9.29 Taking a capillary blood sampleThe blood should flow freely or with very little pressure tothe area. Wipe away the first drop with filter-paper.2. Apply the tip (circled with red) of a capillary tube containingdried heparin to the drop of blood (Fig. 9.30). The bloodflows into the tube by capillarity. Fill about three-quarters ofthe tube.3. Plug the other end of the tube (i.e. the end that has not comeinto contact with the blood) with soft wax or plastic modellingclay (Fig. 9.31). Check that it is completely plugged to adepth of about 2mm.Alternatively, seal the end of the tube by heating it carefully over a Bunsen burneror spirit lamp (Fig. 9.32).Leave it to cool in a horizontal position.It is useful to have ready a numbered stand containing plastic modelling clay, sothat each patient’s tube can be stuck upright next to the corresponding number.Fig. 9.30 Technique for drawing blood into acapillary tubeVenous blood specimens1. Collect a venous blood specimen as described in section 9.2 and add it to atest-tube containing EDTA dipotassium salt solution.