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

286 Manual of basic techniques for a health laboratoryerythrocyte haemoglobin concentration may be as high as 380g/l (haemoglobin(Fe)23.6mmol/l), but it never exceeds these values.The mean erythrocyte haemoglobin concentration is usually called the “mean corpuscularhaemoglobin concentration” (MCHC). It can also be expressed as apercentage. This is calculated by dividing the haemoglobin concentration of theblood in grams per 100ml by the packed cell volume as a percentage and multiplyingby 100.Example:haemoglobin concentration = 15.0g/100mlpacked cell volume = 43%MCHC = (15.0/43) ¥ 100 = 35%.In this system, the reference range is 32–37%. The MCHC never exceeds 38%. Ifsuch a result is obtained, the test should be repeated.9.4.2 Macro-scale methodPrincipleThe blood (mixed with anticoagulant) is placed in a graduated tube and centrifugedto pack the erythrocytes. The level of the column of erythrocytes is then readdirectly in the graduated tube (Fig. 9.36).Materials and reagents (Fig. 9.37)●●●●CentrifugeSpecial graduated tubes (Wintrobe tubes), 9.5cm long with a 0.6-cm bore, calibratedfrom 0 to 100Long fine capillary Pasteur pipette (long enough to reach the bottom of thetube) with rubber teatAnticoagulant — EDTA dipotassium salt, 10% solution (reagent no. 22) orWintrobe solution (reagent no. 65).Fig. 9.36 Principle of themacro scale forestimating theerythrocytevolume fractionMethodCollection of specimens1. Collect a venous blood specimen as described in section 9.2 and add it to agraduated tube containing anticoagulant (see above).2. Using the capillary pipette, fill the graduated tube with blood up to the 100mark, making sure that no air bubbles form (Fig. 9.38).Fig. 9.37 Materials for estimating theerythrocyte volume fraction usingthe macro scaleFig. 9.38 Using a capillarypipette to fill agraduated tubewith blood