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A Diffraction Method for Measuring the Average Volumes and Shapes of Red Blood Cells
Author(s) -
Child J. A.,
King J.,
Newman T. H.,
Waterfield R. L.
Publication year - 1967
Publication title -
british journal of haematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.907
H-Index - 186
eISSN - 1365-2141
pISSN - 0007-1048
DOI - 10.1111/j.1365-2141.1967.tb08751.x
Subject(s) - diffraction , repeatability , shrinkage , optics , centrifuge , constant (computer programming) , intensity (physics) , analytical chemistry (journal) , materials science , chemistry , physics , chromatography , computer science , composite material , nuclear physics , programming language
SUMMARY An instrument and technique are described for determining MCV, MCD and D/T from the visual measurement of the diffraction rings produced by red cells; MCV from the unfixed spherical cells and MCD from the fixed discoidal cells. The method eliminates a serious error due to asymmetry in retinal sensitivity near the fovea. The accuracy of the measurements is assessed from the repeatability of the observations of individual observers, and from the agreement between those of different observers. The validity of the optical theory in the deduction of the cell dimensions from the diffraction measurements is confirmed in the case of spherical cells: (1) By the agreement found between the values of MCV obtained with the spherocytometer on the one hand, and with the electronic counter and centrifuge on the other. (2) By showing that the constants for the various diffraction rings produced by spherical cells have their theoretical values. However, the constants found for the rings produced by the fixed discoidal cells differ significantly from their theoretical values. Because of this, and because of the shrinkage of the fixed cells, the values for MCD and D/T are only relative. The same criticism applies to the standard method for determining these data from dried blood films; but in dried films the shrinkage is variable, whereas in the new method described the shrinkage is constant. Error arising from the intensity of light in a diffraction ring being proportional to the fourth power of the diameter of the cell was examined and found to be negligible in the case of D/T, and to reach a significant amount in MCV only when anisocytosis is extreme. The possibility is considered that in abnormal cells variable shrinkage due to fixation may produce spurious variations in D/T. However, low values for D/T are found in spherocytosis, and high values in thalassaemia, in which the cells are flattened. Further, measurements of unfixed discoidal cells suspended in their own serum gave values of D/T closely parallel to those derived from the fixed discoidal cells. Results may be misleading when a microcytic or macrocytic anaemia is responding to treatment, or following transfusion. The error can be recognized and, by centrifugation, the cells present before treatment can be separated from the newly formed cells and measured in the ordinary way.