Evaluation of the O-cresolphthalein complexone procedure in comparison with the atomic absorption spectrophotometry for serum calcium determination

ABSTRACT

The automated 0.cresophthalein complexone dye method was recently introduced in the calcium chemistry module of the ASTRA-8 system present in Ain Shams University Hospital. This method was evaluated in comparison with the atomic absorption spectrophotometer reference method. Quality control material [normal and pathological levels] and 40 patient samples were used in the evaluation study. The coefficients of variation for the within batch precision were 1.5% and 1.1%, while those for the day to day precision were 3.2% and 2.3% for the normal and pathological levels respectively. Accuracy study showed minimal bias [0.12 mg/dl] and no statistically significant difference was observed between the two methods. Recovery was excellent. Linearity was 4.5 - 13 mg/ dl. No interference was detected by magnesium, while haemoglobin at a level of 1 g/dl showed a decrease in calcium concentration with an average of 0.6 mg/dl. The throughput was 70 samples/ hour, Very small sample size [12 micro l] or reagent [150 micro l] was required. There was good correlation between the ASTRA calcium method and atomic absorption spectrophotometry [Y = 1.97 + 0.8 X r=0.92]. The goals of analytical reliability, simplicity and convenience were nearly achieved by the -ASTRA-8 calcium method: