|Methods for the Evaluation of the Impact of Food and Nutrition Programmes (UNU, 1984, 287 p.)|
|4. Measuring impact using laboratory methodologies|
Haemoglobin concentration can be measured in venous or capillary blood by colorimetric determination of derivatives of hemoglobin such as cyanmethemoglobin, oxyhemoglobin, or acid hematin. Various automated methods exist that are based on some of these principles. The preferred method, as recommended by the International Committee of Standardization in Hematology (14), involves the conversion of ail hemoglobin derivatives except sulfhemoglobin to cyanmethemoglobin by dilution of blood in a solution containing potassium cyanide and potassium ferricyanide. Absorbance is then measured in a photoelectric colorimeter or spectrophotometer at a wavelength of 540 nm. Reference standards of cyanmethemoglobin that conform to the specifications of the ICSH are commercially available.
Comparable information to that obtained from hemoglobin determinations can be obtained by the measurement of the packed red-cell volume, a simple technique that only requires a microcentrifuge and capillary tubes. However, due to changes in the mean corpuscular hemoglobin concentration that occur in iron deficiency anaemia, changes in hemoglobin concentration are more marked than those in the packed cell volume.
Choice of methods for serum iron and total iron-binding capacity (TIBC) will depend on equipment and amount of specimen available. Most current methods consist of the colorimetric measurement of an ironchromogen complex and require a spectrophotometer. The TIBC is determined by adding excess iron to the serum sample and removing unbound iron by some absorbent such as magnesium carbonate. Percent saturation of the TIBC (transferrin) is then calculated. Careful handling of specimens with iron-free material is essential. The Iron Panel of the ICSH has recommended reference methods employing bathophenathroline sulfonate as the colour reagent (15-16). These methods have recently been reviewed in detail (17).
Recommended methods for the determination of FEP (18-19) require a fluorometer and relatively elaborate extraction stages. An alternate method determines Zn protoporphyrin directly from a blood smear using a special apparatus called a hematofluorometer (20). This method is simple, inexpensive, and well adapted for field work, but needs further validation. According to some authors (19), the instrument does not have the precision or accuracy to detect small changes in fluorescence that occur with mild iron deficiency.
Ferritin can be determined in a small amount of serum or plasma by radio-immunoassay (21), and there are several commercial kits that give satisfactory results. The need for radio-isotope facilities has been recently eliminated by the introduction of enzyme immunoassays that only require a spectrophotometer. EIA methods seem to give results comparable to those obtained by RIA. The relatively large variability of results that currently exists among different laboratories may be reduced in the future by the use of ferritin standards that are becoming available from the ICSH.