Assessment of iron deficiency and anemia

Numerous indicators for assessing anemia and iron status are available. These include serum ferritin, transferrin concentration and saturation, transferrin receptor, erythrocyte protoporphyrin, hemoglobin, hematocrit, and erythrocyte morphology and color (Table 22.2).

Assessment of Iron Deficiency and Iron-Deficiency Anemia [9, 11]

Indicator

Measure

Cutoffs

Indication

Commonly used methods

Special considerations in developing countries

Serum Ferritin

Total body iron stores

<12mcg/P

Depleted iron stores

Venous or capillary blood, dried blood spots (DBS) ELISA method

Infection and inflammation may cause inflated ferritin values Use of DBS convenient for field work

Serum transferrin concentration (TIBC)

Concentration of iron-transport protein

360mcg/dl

390mcg/dl 410mcg/dl

Depleted iron stores

Iron-deficient erythropoiesis Iron-deficiency anemia

Venous blood

Assay in which transferrin is saturated with excess iron; chromogenic methods

Influenced by infection and inflammation

More complicated laboratory procedure that requires quality-control sera

Serum transferrin saturation

Iron transport protein

<15%

Iron-deficient erythropoiesis

Venous blood

Calculated from TIBC and serum iron values

Influenced by infection and inflammation

Diurnal variation

Soluble serum transferrin receptor (STfR)

Expression of STfR, which bind ferritin for uptake in cells

>8.5mg/l 14mg/l

Iron-deficient erythropoiesis

Iron-deficiency anemia

Venous blood ELISA method

Possible to quantify STfR using a dried blood spot

Generally not significantly influenced by infection and inflammation

Can be influenced by other nutritional deficiencies such as B12 and folate deficiency and specifically by acute malaria infection

(continued)

Free erythrocyte protoporphyrin

(FEP)

Serves as an intermediate in heme biosynthesis

>70mmol FEP/ mol heme

Iron-deficient erythropoiesis

Whole blood (drop) Hemotofluorometry

Influenced by infection and inflammation

Portable hemafluorometer available

Hemoglobin

Blood hemoglobin concentration

<11 g/dl

Anemia in pregnant women

Venous or capillary blood Dried blood spot

Influenced by certain parasitic infections and other micronutrient deficiencies

<12g/dl

Anemia in nonpregnant women >15 years

HemoCue or cyanmethemoglobin method

It is necessary to make adjustments to cutoff values for persons living in high altitudes

Less expensive, field friendly equipment available

Hematocrit

Packed red blood cell volume

36% 33%

Anemia in nonpregnant women >15 y

Anemia in pregnant women

Whole blood Centrifugation method

Less expensive, but methods can be difficult to standardize in a field setting

Erythrocyte

Color and shape or erythrocyte

Microcytic or hypochromic

Anemia

Whole blood Microscopy

aWHO recommends using a serum ferritin cutoff of <15mcg/l in areas where infections such as malaria are prevalent aWHO recommends using a serum ferritin cutoff of <15mcg/l in areas where infections such as malaria are prevalent

As outlined below, certain indicators are more appropriate for use in field settings in developing countries with limited resources and laboratory capacity and high rates of parasitic diseases. In very resource-poor settings where access to a laboratory or laboratory equipment is limited or not possible, clinical examination to detect iron-deficiency anemia might be the only option [3].

Iron is stored in the body primarily in the protein ferritin, which is an indicator used to determine iron stores [8]. Serum ferritin concentrations are commonly determined in venous or capillary blood or dried blood spots using enzyme-linked immunosorbent assays (ELISA) or two-site immunoradiometric assays [9, 10]. Infection and inflammation can falsely elevate serum ferritin concentration, and this is a concern in developing countries where parasitic diseases are common [11]. Iron is transported through the body bound to the transport plasma protein transferrin, which can be measured in venous blood. Both transferrin saturation and transferrin concentration (total iron binding capacity [TIBC]) can serve as indicators for iron deficiency. Transferrin can be measured using chromogenic methods. Ferritin uptake into cells is regulated by transferrin receptors, which are expressed on cell surfaces and can be measured. Elevated expression of serum transferrin receptors, measured using ELISA techniques, can indicate iron-deficient erythropoiesis [12, 13].

Free erythrocyte protoporphyrin (FEP) serves as an intermediate in heme biosynthesis. Elevated FEP concentrations can indicate an interruption in heme synthesis due to iron deficiency and a subsequent build-up of the FEP precursor. FEP can be measured in whole blood, using hematofluorometry [11].

Seventy percent of iron in the body is contained in hemoglobin, an erythrocyte protein that transports oxygen from the lungs to tissues in the body. Hemoglobin concentration is commonly used to diagnose anemia in developing countries because the determination is relatively inexpensive and generally does not require complicated laboratory procedures. Hemoglobin can be measured using a portable photometer such as a HemoCue™, which is battery operated and can be used in a field setting. Determination of hemoglobin concentration using a HemoCue™ requires a capillary blood sample, obtained from either a finger, ear, or heel prick, or a small amount of blood from a whole blood sample (10 |l) (www.hemocue.com). Hemoglobin concentration can also be determined using the cyanmethemoglobin method, which requires the dilution of venous blood and analysis by a spectrophotometer. Hematocrit, the packed red cell volume in whole blood, can be determined by centrifugation using venous or capillary blood. Although this method is relatively simple, factors, including measurement error, can influence the precision, specificity, and sensitivity of the test [9]. Both hemoglobin and hematocrit concentrations can be influenced by other factors that might influence erythrocyte production and cause anemia. These include parasitic infections and other nutritional deficiencies (i.e. B12, folate, vitamin A), which are of special concern in developing countries.

Ideally, these indicators should be used in combination to determine iron deficiency and iron-deficiency anemia. For example, serum ferritin and transferrin receptor measures can be used in conjunction with hemoglobin measures to determine whether anemia is caused by iron deficiency. The most recent recommendations by WHO for monitoring programs that aim to prevent and control iron deficiency and anemia have been to include hemoglobin and serum ferritin [14].

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