Development of a new measurement method for serum calcium with chlorophosphonazo-III.
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 Mg(2+), Fe(2+), Cu(2+) and Zn(2+). 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 degrees C without daily calibration.


CONCLUSIONS
The new calcium measurement method in serum was demonstrated to have reliable and acceptable performances as a routine test in clinical laboratory.
Hokazono
Eisaku
E
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, Japan. hokazono@shs.kyushu-u.ac.jp
Osawa
Susumu
S
Nakano
Tomota
T
Kawamoto
Yukari
Y
Oguchi
Yuji
Y
Hotta
Taeko
T
Kayamori
Yuzo
Y
Kang
Dongchon
D
Cho
Yuichiro
Y
Shiba
Kiyoko
K
Sato
Kenji
K
D002118:Calcium / Q000097:blood* / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry*; D006801:Humans; D007202:Indicators and Reagents / Q000737:chemistry*; D015394:Molecular Structure; D013054:Spectrophotometry, Atomic
D002614:Chelating Agents; D007202:Indicators and Reagents; D002118:Calcium