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

9. Haematology 285concentration is about 8.0mmol/l, and the erythrocyte volume fraction will be about8.0 ¥ 0.05 = 0.4.Additional information provided by the erythrocyte volume fraction testExamine the layer of leukocytes just above the column of erythrocytes (see Fig.9.34). It is normally very thin; if it seems thick, determine the leukocyte numberconcentration (see section 9.6). The layer will seem abnormally thick if the leukocytenumber concentration is greater than 20 ¥ 10 9 /l. In cases of leukaemia, when theleukocyte number concentration may be 100–200 ¥ 10 9 /l, the layer may be severalmillimetres thick.Mean erythrocyte haemoglobin concentrationThe mean erythrocyte haemoglobin concentration is a measure of the average haemoglobincontent of the erythrocytes. It is expressed either in grams of haemoglobinper litre or in millimoles of haemoglobin(Fe) per litre 1 and is calculated bydividing the haemoglobin concentration of the blood by the erythrocyte volumefraction.Example:●If the haemoglobin concentration is expressed in grams of haemoglobin perlitre:haemoglobin concentration = 150g/lerythrocyte volume fraction = 0.43mean erythrocyte haemoglobin concentration = 150/0.43 = 349g/l (or 34.9%).● If the haemoglobin concentration is expressed in millimoles of haemoglobin(Fe)per litre:haemoglobin(Fe) = 9.3mmol/lerythrocyte volume fraction = 0.43mean erythrocyte haemoglobin concentration = 9.3/0.43 = 21.6mmol/l.Note: to convert values in g/l to values in mmol/l, multiply by 0.06206. Thus, usingthe above example, 349g/l ¥ 0.06206 = 21.6mmol/l.Reference valuesNormally the mean erythrocyte haemoglobin concentration lies between the followinglimits:— lower limit: haemoglobin 322g/l or haemoglobin(Fe) 20mmol/l;— upper limit: haemoglobin 371g/l or haemoglobin(Fe) 23mmol/l.When the value falls within this range, the erythrocytes are said to be “normochromic”(i.e. of normal colour).Values below the lower limit of the reference range indicate that the erythrocytesare “hypochromic” (i.e. less coloured than normal). Low values are found in patientswith hypochromic anaemia.If the value is higher than the upper limit of the reference range, the mean erythrocytehaemoglobin concentration should be determined again. Haemoglobin formsabout 95% of the erythrocyte mass. Therefore, erythrocytes are never “hyperchromic”(i.e. more coloured than normal), but they may increase in volume and thusbe capable of containing more haemoglobin than normal; in this case the mean1See note about expression of haemoglobin concentration on page 284.