Blood samples for packed cell volume (PCV) estimation are obtained from either the veins or capillaries. However, the volume of red cells in capillary blood varies from venous blood. The extent of this variation as well as its impact on the diagnosis of anaemia has not been studied in pregnancy. To determine whether capillary blood PCV differed from venous blood PCV of apparently healthy pregnant women in Enugu, Nigeria, as well as the effect of the source of blood on prevalence of anaemia in pregnancyPCV was estimated using pairs of venous and capillary blood samples collected from a cohort of 200 consecutive pregnant women at the antenatal clinic of UNTH Enugu. Questionnaires were used to obtain data on participant’s arm preference for blood sample collection. Data analysis was both descriptive and inferential at 95% confidence level. The mean capillary PCV (cPCV) of participants was 33.5 ± 3.57% while that of venous PVC (vPCV) was 34.3 ± 3.74% (P < 0.001). The difference between cPCV and vPCV pairs ranges from -5% to +5% (mean = -0.83 ±1.54). Prevalence of anaemia was 33.5% or 28.0% using the capillary or venous blood respectively [O.R = 1.3 (CI 95%: 0.85, 1.98)]. A majority (47.5%) of participants did not express any specific arm preference for blood sample collection. PCV from capillary blood is significantly lower than that of venous blood among normal pregnant women in Enugu, Nigeria. Likewise the prevalence of anaemia in pregnancy derived from cPCV is higher than that of vPCV. Maternity units should use venous blood for PCV estimation.



1.1       Background
1.2       Study justification
1.3       Study hypothesis
1.4       Aim and objectives
1.41     Aim
1.42     Objectives

2.1       Human blood and pregnancy
2.2       Physiologic anatomy of the capillary and vein
2.3       Anaemia and pregnancy
2.4       Capillary and venous haematocrit

3.1       Study center
3.2       Study area
3.3       Patients
3.4       Eligibility
3.5       Exclusion criteria
3.6       Study design and sample selection
3.7       Sample size determination
3.8       Ethical clearance
3.9       Data collection and analysis
3.10     Quality control measures
3.11     Primary outcome measure
3.12     Secondary outcome measures

4.1       Socio-demographic characteristics
4.2       Capillary and venous packed cell volume
4.3       Anaemia in pregnancy and its variation with source of blood
4.4       Arm preference for blood sample collection

5.1       Discussion
5.2       Conclusion
5.3       Recommendations


1.1     Background                    

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.

1.2     Study justification  

Pregnancy is a physiological condition characterized by lots of systemic changes necessary to support the growth of the fetus. Though most pregnancies are normal, complications often arise causing varying degrees of maternal and perinatal morbidity and mortality. A very important complication of pregnancy in sub-Saharan Africa is anaemia. A report from the study area showed a high prevalence (41.9%) of anaemia among pregnant women at booking (Dim and Onah, 2007).
Blood samples for assessment of PCV are often collected from the veins or the capillaries and the results got are accepted without regards to the source of the specimen. Most often, especially in emergency situations, the capillary blood sample from finger pricks are often used for PCV estimation probably because it is easier and faster. However, because of peculiarities of blood and the capillary microcirculation, it has been shown that the volume of red cells in capillary blood varies from that of the venous blood (Baskurt et al., 2006). This disparity between capillary and venous blood PCV has been reported in several studies (Daae et al., 1988; Daae et al., 1991; Yang et al., 2001) but none of them involved pregnant women. It is not known whether pregnancy state attenuates the disparity or worsens it. The concern is heightened by the fact that PCV results from both capillary and venous blood are used interchangeably in the study area Therefore, it becomes very important to study the similarity or otherwise of capillary and venous PCV in pregnancy. This will ensure uniformity as regards the diagnosis of anaemia in pregnancy.

On the other hand, it is expected that patient’s arm preference should be sought for and respected by a caregiver / phlebotomist during the collection of blood sample for any investigations (University of Virginia (UVA) Health System, 2011); this should be more important during antenatal care because a majority of pregnant women are healthy. However, this consideration does not seem to be the practice in the study area based on the investigator’s personal observation. Therefore, in order to initiate and encourage the practice of seeking for and respecting arm preference during blood sample collection from pregnant women at the study center, it is important to demonstrate that this group of women do have varying arm preferences..... 

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