Establishment of reference intervals of clinical chemistry analytes for the adult population in Egypt

Abstract

Background: This is the first Egyptian nationwide study for derivation of reference intervals (RIs) for 34 major chemistry analytes. It was conducted as a part of the global initiative by the IFCC Committee on Reference Intervals and Decision Limits (C-RIDL) for establishing country-specific RIs based on a harmonized protocol.

Methods: 691 apparently healthy volunteers aged ≥18 years were recruited from multiple regions in Egypt. Serum specimens were analyzed in two centers. The harmonization and standardization of test results were achieved by measuring value-assigned serum panel provided by C-RIDL. The RIs were calculated by parametric method. Sources of variation of reference values (RVs) were evaluated by multiple regression analysis. The need for partitioning by sex, age, and region was judged primarily by standard deviation ratio (SDR).

Results: Gender-specific RIs were required for six analytes including total bilirubin (TBil), aspartate and alanine aminotransferase (AST, ALT). Seven analytes required age-partitioning including glucose and low-density lipoprotein cholesterol (LDL-C). Regional differences were observed between northern and southern Egypt for direct bilirubin, glucose, and high-density-lipoprotein cholesterol (HDL-C) with all their RVs lower in southern Egypt. Compared with other collaborating countries, the features of Egyptian RVs were lower HDL-C and TBil and higher TG and C-reactive protein. In addition, BMI showed weak association with most of nutritional markers. These features were shared with two other Middle Eastern countries: Saudi Arabia and Turkey.

Conclusion: The standardized RIs established by this study can be used as common Egyptian RI, except for a few analytes that showed regional differences. Despite high prevalence of obesity among Egyptians, their RVs of nutritional markers are less sensitive to increased BMI, compared to other collaborating countries.

Fig 1. Sex and age-related changes of selected parameters.

RVs were partitioned by sex (male: M, female: F) and age-subgroups (~29, 30~39, 40~49, 50~). The box in the center of each scattergram indicates the mid 50% range of RVs, and its central vertical bar represents the median. The data size is shown at the right bottom of the age group labels. Because no secondary exclusion was done for RVs, the range of the scatter plot may not match to the RI to be determined.

Fig 2. Side-by-side comparison of RVs for TBil, TG, HDL-C, and CRP between Egyptian and other population.

RVs of ten countries were compared by box-whisker charts. The box represents central 50% ranges, the vertical bar at the box represents the median. The span of the horizontal bar represents central 95% interval. The countries were subgroups by ethnicity: Middle Easterners: “Saudi Arabia, Turkey” with the central box shaded in red, Asians: “Japan, China, India” shaded in blue, and Caucasians: “USA, Russia, Argentina, South African Caucasians (ZA-Cau)” shades in green. The full-range vertical line represents median RV of Egyptian male (blue) and female (red).

Fig 3. Ethnic differences in regression line between BMI and RVs of nutritional markers.

Comparison of least-square linear regression lines between BMI and RVs of six nutritional markers among ten countries: Middle Easterners: “Egypt, Saudi Arabia, Turkey” in graded red, Asians: “Japan, China, India” in graded blue, and Caucasians “USA, Russia, Argentina, South African Caucasians (ZA-Cau)” in graded green.