CHAPTER ONE INTRODUCTION 1.1 Background of the study Blood is a specialized fluid made up of cells suspended in plasma. It is essentially confined within the blood vessels which vary in structure and function, depending on the type. The capillaries connect the arterial to the venous vascular system and are responsible for the exchange of gases and nutrients between cells and the blood. Only 5% of the blood is in the capillaries and in dilated state, the calibre of the capillary is just sufficient to permit red blood cells (RBC) to squeeze through it in a single file (Ganong, 2005). Some sites such as the fingers, ear lobes, and the heels have extensive capillary network and are often used for the collection of blood samples for laboratory investigations, especially packed cell volume (PCV) or haematocrits (Hct), which is one of the most widely measured parameters in medical practice (Baskurt et al., 2006). On the other hand, the veins have intact walls and transmit blood from the capillaries, through the venules, to the right chamber of the heart. They are superficial when compared to the arteries, especially in the limbs, and are used for collection of blood specimen for haematological and other investigations. Anaemia is defined as having below normal values for the total volume of red blood cells, the number of normal red blood cells, or the amount of hemoglobin in these cells (USAID, 1997). The proportion of blood made of red blood cells is referred to as the Hct or PCV. In pregnancy, anaemia implies a PCV of less than 33% or a haemoglobin concentration of less 11gm% (WHO, 1992). Anaemia in pregnancy continues to be a major health problem in many developing countries and is associated with increased rates of maternal and perinatal mortality, premature delivery, low birth weight, and other adverse outcomes (Mahomed, 2004; Nyuke and Letsky, 2000). More than half of the pregnant women in the world have haemoglobin levels indicative of anaemia (WHO, 1992). However, while only 15% of pregnant women are anaemic in developed countries, the prevalence of anaemia in developing countries is relatively high (33-75%) (Dim and Onah 2007; Massawe et al., 1999; Nyuke and Letsky, 2000; WHO, 1992). The commonest cause of anaemia in pregnancy worldwide is iron deficiency (Nyuke and Letsky, 2000). The predisposing factors include grandmultiparity, low socio-economic status, malaria infestation, late booking, Human Immunodeficiency Virus (HIV) infection, and inadequate child spacing amongst others (Adinma et al., 2002; Aimaku et al, 2003; Aluka et al., 2001; Amadi et al., 2000). Pregnant women are therefore screened for anaemia during antenatal service and placed on prophylactic oral iron therapy. This is an important secondary preventive health strategy aimed at early detection and treatment of anaemia in pregnancy.
It has been shown that the red cell volume of capillary blood is less accurate when compared to that of venous blood, especially in severe anaemia (USAID, 1997). In pregnancy, there is marked physiological and anatomical changes including the disproportionate increase in blood volume and red blood cell mass (Koos and Moore, 2003). These changes may affect the accuracy of capillary blood PCV which may negatively influence the diagnoses and management of anaemia in pregnancy.