Reference value of immunoglobulins in healthy school children of Bangladesh.

The reference value of immunoglobulins (Igs) should be known for a population concerned because it is influenced by many clinical and local conditions. As yet the reference value of the Igs have not been determined in Bangladeshi children. This study determined the reference value of Igs in apparently healthy 261 rural Bangladeshi primary school children (aged 5 to 14 years, mean 9.3 years). IgG, IgM and IgA were determined by an auto-analyzer. The mean (standard deviation) value of IgG was 1728 (344) mg/dl. The corresponding values for IgM and IgA were 200 (88) and 163 (63) mg/dl, respectively. The 95% reference value calculation in all subjects showed that the range for IgG was 1103 to 2524, IgM was 92 to 390, and IgA was 72 to 325 mg/dl. These values could be used to evaluate Ig status in children with a variety of clinical conditions.


INTRODUCTION
Human body is equipped with a special system of defense mechanism. The chief armor of the defense mechanism is immunoglobulins (Ig), which are the effector products of dif- Therefore, it is necessary to determine the reference value in the population under question.
In Bangladesh, no report is available on normal level of Igs in children. This study was done to find out the normal level of IgG, IgM and IgA in healthy school children of Bangladesh.

MATERIALS AND METHODS
Primary education in Bangladesh consists of five years from grades I through V and is free of cost. Usually children enroll in to primary schools at 5 to 6 years of age, but there is no strict rule. This study was done, during February through May 1992, in Sanora Government Primary School located in Sanora village of Dhamrai upazilla (sub-district) in Dhaka district. Children of all socioeconomic status from the nearby area attend this school. It is run by a management committee, which consists of representatives of parents, teachers and government officers. A meeting was held between the investigators and management committee, which also included the local health authority. Consent was obtained from the management committee. Then class teachers explained the purpose of the study to the students and requested them to participate in the study. A total of 450 boys and girls of all grades participated in the study. We excluded those who suffered from fever and sore throat during the last four weeks, and those who had clinical evidence of tons illo-pharyngitis on physical examination. None of them suffered from immunodeficiency diseases. Thus, 361 (80.2%) children were selected for laboratory investigation. Among them 261 (72.2%) subjects were finally selected for this study after excluding those with C-reactive protein more than 0.05 mg/dl 1) and yielded bacteria on throat culture (mostly streptococci and staphylococci). Blood samples were collected in fasting condition and sera were separated within two hours of venepuncture and preserved in -80°C until mea-  Table 2. Mean (standard deviation) and percentile distribution of immunoelobulins (mg/dl) childhood. Therefore, they attain adult level of Igs before adulthood, and age-dependent changes in childhood become masked.

Possible bias:
To recruit healthy children we have excluded those who had fever during last month, and tested positive for throat swabs and C-reactive protein. This definition for healthy children does not necessarily ensure inclusion of healthy children (and exclusion of sick children).

Implication:
In absence of a recognized reference range of Ig, determination of immune status would vary among physicians. We believe that the reference values suggested here would reduce such variations and may help in diagnosis and therapeutic decision making. On the other hand, the cut-off points for the reference value on a continuous test result is an arbitrary decision 9). This is true for any test result that takes on a range of values 10) Physicians should use their clinical judgement for decision making. As the immunoglobulin distributions are heterogeneous among the population, it is necessary to determine the distribution of Igs for the population concerned. However, in absence of data for the population under question, present data may provide some information for developing countries especially South Asian countries.

ACKNOWLEDGMENTS
This analysis is based on the routine work done by many other investigators of the National Center for Control of Rheumatic Fever and Heart Diseases. We are indebted to them. We extend special thanks to JICA (Japan International Cooperation Agency) experts who worked as counterpart in this Center during the study period. We are grateful to the teachers, parents and students of Sanora Primary School for their cooperation.