Consistency between calculation results of ionized calcium formula method and direct determination results of ion-selective electrode method

doi:10.3969/j.issn.1673-8640.2025.10.002

Abstract

Abstract:

Objective To investigate the consistency between the results of the formulas for calculating ionized calcium（formula method） and the direct determination results using ion-selective electrode（ISE） method. Methods The determination results of total calcium，ionized calcium，total carbon dioxide（TCO₂），bicarbonate ion（HCO₃^-），total protein（TP），albumin（Alb） and chloride ion（Cl^-） for 6 148 patients in the outpatient and inpatient departments of Renji Hospital Affiliated to Shanghai Jiao Tong University School of Medicine from July to December 2023 were collected. The ionized calcium determination results were calculated using 4 formulas [self-built formula 1（multivariate linear stepwise regression method），self-built formula 2（automatic linear modeling），Forster 1985 formula，Nordin 1989 formula] and compared with ISE method. Results The ionized calcium determination results of self-built formula 1，self-built formula 2，Forster 1985 formula and Nordin 1989 formula were all positively correlated with ISE method（r values were 0.660，0.659，0.478 and 0.222，respectively，P<0.05）. Taking the ISE method's ionized calcium determination results as the reference，the compliance threshold of formula method was set as ±10%. When the ISE method's ionized calcium determination results were 0.99-1.40 mmol·L^-1，the consistency of formula method was the highest，from high to low，they were self-built formula 1（95.93%），self-built formula 2（95.52%），Forster 1985 formula（90.78%） and Nordin 1989 formula（52.91%）. When the ISE method's ionized calcium determination results were ≤0.98 mmol·L^-1，the cosistency of formula method was <40%，and the formula method results were higher than that of ISE method（P<0.001）. When the ISE method's ionized calcium determination results were ≥1.41 mmol·L^-1，the consistency of formula method from high to low were Forster 1985 formula（76.19%），self-built formula 2（58.73%），self-built formula 1（41.27%） and Forster 1985 formula（41.27%），and the formula method results were lower than that of ISE method（P<0.001）. Conclusions When the ionized calcium level was 0.99-1.40 mmol·L^-1，except for Nordin 1989 formula，the consistency rates of the other formulas with ISE method are all relatively high. When the ionized calcium was ≤0.98 mmol·L^-1 or ≥1.41 mmol·L^-1，the differences between formula method and ISE method were significant，and the actual level of ionized calcium would be overestimated or underestimated.

Key words: Ionized calcium, Ion-selective electrode method, Self-built formula, Forster 1985 formula, Nordin 1989 formula

CLC Number:

R446.1

LIN Weiwei, XU Jingsong, ZHANG Lele, LI Min, WANG Hua. Consistency between calculation results of ionized calcium formula method and direct determination results of ion-selective electrode method[J]. Laboratory Medicine, 2025, 40(10): 941-945.

Figures/Tables 4

References 13

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项目	总钙/（mmol·L^-1）	Na⁺/（mmol·L^-1）		Cl^-/（mmol·L^-1）	TP/ （g·L^-1）	Alb/ （g·L^-1）	TCO₂/（mmol·L^-1）	HCO₃^-/（mmol·L^-1）
$\bar{x}\pm s$	2.20±0.19	141.42±3.88		105.11±4.74	66.41±9.46	38.48±6.72	33.40±14.52	25.34±3.47
范围	1.13~3.37	108.00~164.00		69.00~129.00	25.80~138.70	10.50~57.80	6.10~89.50	6.40~45.60
项目	AG/（mmol·L^-1）	离子钙/（mmol·L^-1）
项目	AG/（mmol·L^-1）	ISE法	自建公式1	自建公式2	Forster 1985公式	Nordin 1989公式
$\bar{x}\pm s$	10.96±3.07	1.15±0.10	1.15±0.07	1.16±0.07	1.15±0.09	1.15±0.16
范围	1.60~30.00	0.23~1.70	0.77~1.50	0.76~1.56	0.59~1.86	0.49~1.93

项目	总钙/（mmol·L^-1）	Na⁺/（mmol·L^-1）		Cl^-/（mmol·L^-1）	TP/ （g·L^-1）	Alb/ （g·L^-1）	TCO₂/（mmol·L^-1）	HCO₃^-/（mmol·L^-1）
$\bar{x}\pm s$	2.20±0.19	141.42±3.88		105.11±4.74	66.41±9.46	38.48±6.72	33.40±14.52	25.34±3.47
范围	1.13~3.37	108.00~164.00		69.00~129.00	25.80~138.70	10.50~57.80	6.10~89.50	6.40~45.60
项目	AG/（mmol·L^-1）	离子钙/（mmol·L^-1）
项目	AG/（mmol·L^-1）	ISE法	自建公式1	自建公式2	Forster 1985公式	Nordin 1989公式
$\bar{x}\pm s$	10.96±3.07	1.15±0.10	1.15±0.07	1.16±0.07	1.15±0.09	1.15±0.16
范围	1.60~30.00	0.23~1.70	0.77~1.50	0.76~1.56	0.59~1.86	0.49~1.93

公式	ISE法≤0.98 mmol·L^-1		ISE法≥1.41 mmol·L^-1
公式	例数	符合^①/[例（%）]	例数	符合^①/[例（%）]
自建公式1	304	113（37.17）	63	26（41.27）
自建公式2	304	109（35.86）	63	37（58.73）
Forster 1985公式	304	89（29.28）	63	48（76.19）
Nordin 1989公式	304	79（25.99）	63	26（41.27）

公式	ISE法≤0.98 mmol·L^-1		ISE法≥1.41 mmol·L^-1
公式	例数	符合^①/[例（%）]	例数	符合^①/[例（%）]
自建公式1	304	113（37.17）	63	26（41.27）
自建公式2	304	109（35.86）	63	37（58.73）
Forster 1985公式	304	89（29.28）	63	48（76.19）
Nordin 1989公式	304	79（25.99）	63	26（41.27）