COMPARISON OF SERUM CALCIUM ESTIMATION BY DIRECT COLORIMETRIC AND VOLUME / VOLUME COLORIMETRIC METHODS BASED ON O-CRESOLPHTALEIN PRINCIPLE

Introduction: Calcium is the most abundant mineral and fifth most common element in the body. There are many different methods for estimation of serum calcium like spectrophotometeric, ion selective electrode (ISE) and atomic absorption methods. Objective: Aim of our study was to compare serum calcium estimation by using direct colorimetric and volume / volume colorimeteric (v/v) methods based on o-Cresolphtalein principle. Materials and Methods: The study was performed in a tertiary care laboratory in Rawalpindi from March to June ‘2011. It was a comparative prospective study. Seventy commercial quality control samples of Randox laboratories were simultaneously tested by both the methods. Results were analyzed on SPSS version 17. Results: In normal controls, the v/v method kit gave the mean result of 2.34 mmol/L ± 0.04 with a CV of 1.70% while with the direct colorimetric method kit the values were 2.31 mmol/L ± 0.03 with a CV of 1.30%. In abnormal controls, v/v method kit gave the mean value to be 3.09 mmol/L ± 0.04 with a CV of 1.29% while with the direct colorimetric method kit, the mean value was 3.07 mmol/L ± 0.03 with a CV of 0.97%. Conclusion: Both the kits are recommended for use in a tertiary care laboratory as the precision and accuracy of both kits is comparable. But the volume / volume colorimetric kit is more cost effective.