July 1989, Volume 39, Issue 7



Farida Agha  ( PMRC Research Centre, Jinnah Postgraduate Medical Centre, Karachi. )

Diagnostic distinction between iron defi­ciency anaemia and other causes of a falling hae­moglobin level is a problem in antenatal care1. Anaemias occurring during pregnancy are known to increase maternal and perinatal morbidity and mortality2 and, therefore, it would be of thera­peutic importance to select women who are iron deficient prior to their developing a frank iron deficiency anaemia. However, diagnosis of iron deficiency is difficult, even in non-pregnant wo­men3,4. A large overlap exists in the distribution of haemoglobin concentration between normal in­dividuals and those who are iron deficient. Chan­ges in the blood volume and composition (eg. haemodilution) make the diagnosis of iron defi­ciency in pregnancy even more difficult than that in non-pregnant state.2,3,5,6 The use of non-preg­nant standards to define normality or deficiency during pregnancy is often misleading. During pregnancy, the rate of iron metabo­lism increases in many ways. Enhanced absorp­tion, increased mobilization of storage iron and elevated serum transferrin concentration accle­rate iron turn over1. Red cell mass is considerably increased7,8 but because of a greater rise in plasma volume, a certain degree of haemodilution almost always occurs. This results in a fall of baemoglobin concentration and haematocrit values as well as in the red cell count, even though red cell mass ac­tually increases, invalidating the diagnostic value of these conventional laboratory measurements. Serum iron and TIBC or serum transferrin con­centrations are used to identify iron deficiency10. However, serum iron values show much day to day and even hour to hour variation11 and transferrin concentration is always increased during pregnan­cy10-13. The most sensitive way of measuring iron deficiency is the assessment of body iron stores. Measurement of actual iron stores and their chan­ges in pregnancy are of crucial importance when distinguishing between iron deficiency and other causes (eg. haemodilution) of a falling haemo­globin level13. The falling concentration of blood haemogjobin cannot be attributed to iron deficien­cy if there are demonstrable stores of unused iron in the body. Until recently there has not been any simple way of estimating iron stores or quantitating the changes of storage iron during pregnancy. 13,14 Es­timation of the bone marrow stainable iron has been used to evaluate iron stores during pregnan­cy, but the method is semiquantitativ; laborious and also inconvenient to the patient12,15,16. Ob­viously, there is need for better diagnostic criteria for iron deficiency during pregnancy. Serum fer­ritin assay adds a new tool for investigating iron metabolism during pregnancy, its concentration accurately reflects the level of body iron stores during pregnancy16-21. The procedure is far easier than other methods for estimating iron stores. A low serum ferritin concentration always indicates depleted iron stores, and iron deficiency seems to be the only condition associated with decreased serum ferritin concentration. 14,16 it is sometimes difficult to distinguish between iron deficiency an­aemia and infectious anaemia, since the serum iron and transferrin saturation can be low in both the conditions3,4,10,14, but the fact that serum fer­ritin concentration is increased with infections adds to its diagnostic value. The changes that occur in serum ferritin concentration during and after normal pregnancy are in accordance with the iron balance calculations for iron needs during pregnancy17. Serial measurements of serum fer­ritin concentration during normal pregnancy show that if no exogenous iron is given, all women, irrespective of the initial size of their iron stores have depletediron stores at the time of delivery17,18,21. Serum ferritin determination is, at present, the best single measurement to detect iron defi­ciency during pregnancy. If anaemia (low blood Hb.) is associated with a low serum ferritin con­centration during pregnancy, diagnosis of iron de­ficiency anaemia can almost invariably be made.


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