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

300 Manual of basic techniques for a health laboratoryFig. 9.63 Cleaning slides to be used for thin blood filmsTo make a spreader, select a slide with a perfectly smooth edge. Make a diagonalmark across the two corners at one end of the slide with a file. Snap off the two filedcorners (Fig. 9.64).9.10.3 MethodCollection of specimensTake the blood from the side of the third or fourth finger as shown in Fig. 9.29.Let the blood flow freely. First take samples for determining the erythrocyte orleukocyte number concentrations, if possible (see sections 9.5 and 9.6).Important:Do not take blood from:— the index finger or thumb— an infected finger (e.g. paronychia)— the ear (too many monocytes).If it is not possible to prepare the film within 1–2 hours of collection of the bloodspecimen, EDTA dipotassium salt solution should be added. Other anticoagulantssuch as heparin alter the appearance of leukocytes and thrombocytes and shouldnot be used.Preparation of the film1. Collect a drop of blood of about 4mm diameter by touching it lightly with oneend of the slide (Fig. 9.65).2. Hold the slide with one hand. Using the other hand, place the edge of the spreaderjust in front of the drop of blood (Fig. 9.66).