Annals of Clinical Biochemistry > Volume 46, Number 4 > Pp. 296-301

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Original Articles

Development of a new measurement method for serum calcium with chlorophosphonazo-III

Eisaku Hokazono^1,2, Susumu Osawa¹, Tomota Nakano³, Yukari Kawamoto³, Yuji Oguchi³, Taeko Hotta⁴, Yuzo Kayamori⁴, Dongchon Kang^4,5, Yuichiro Cho², Kiyoko Shiba⁶ and Kenji Sato²

¹ Department of Health Sciences, Division of Biological Science and Technology, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582; ² Anatomy and Physiological Science Department of Life Sciences and Bio-informatics, Division of Biomedical Laboratory Sciences, Graduate School of Health Sciences, Tokyo Medical and Dental University, Tokyo; ³ Clinical Department of Isehara Research Laboratory, Technology & Department, Division, Kanto Chemical Co. Inc., Kanagawa; ⁴ Department of Clinical Chemistry and Laboratory Medicine, Kyushu University Hospital, Fukuoka; ⁵ Department of Basic Medicine, Faculty of Medical Sciences, Kyushu University, Fukuoka; ⁶ Department of Clinical Laboratory Medicine, School of Health Science Technology, Bunkyo Gakuin University, Tokyo, Japan

Corresponding author: Eisaku Hokazono, Anatomy and Physiological Science Department of Life Sciences and Bio-informatics, Division of Biomedical Laboratory Sciences, Graduate School of Health Sciences, Tokyo Medical and Dental University, Tokyo, Japan. Email: hokazono{at}shs.kyushu-u.ac.jp

Background: Although serum calcium has been measured using the o-cresolphthalein complexone (oCPC) method in the clinical laboratory, this method still has some problems regarding linearity and reagent stability. We developed a new measurement procedure using chlorophosphonazo-III (CPZ-III: 2,7-bis (4-chloro-2-phosphonophenylazo) -1,8- dihydroxy-3, 6-naphthalenedisulphonic acid, disodium salt) as a chelator with an acid medium for serum calcium measurement. The present method showed better linearity and reagent stability compared with the oCPC method.

Methods: Characteristics were studied in optimized conditions measuring wavelength by absorption spectra analysis, and interference of protein and metals with Mg²⁺, Fe²⁺, Cu²⁺ and Zn²⁺. The method was applied to an automated analyser (7170; Hitachi High Technologies Corp). The measurement performance was evaluated for accuracy, precision, recovery rate, linearity and reagent stability with a comparison study against atomic absorption spectrophotometry (AAS).

Results: The within-run and between-run variations (coefficient of variation [CV]) were 0.92–1.01% and 0.75–1.43%, respectively. The linearity was 0–7.0 mmol/L. The comparison study obtained y = 1.002x (AAS) – 0.10, Sy/x = 0.18 mmol/L, n = 50. Reagent stability was at least 20 d at 4°C without daily calibration.

Conclusion: The new calcium measurement method in serum was demonstrated to have reliable and acceptable performances as a routine test in clinical laboratory.

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