Potential over-the-limit correction of serum sodium concentration owing to device performance
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CE-RESEARCH LETTER TO THE EDITOR
Potential over‑the‑limit correction of serum sodium concentration owing to device performance Masayuki Tanemoto1,2 · Hiroaki Tsubata3 · Hikaru Oouchi3 · Yukio Okazaki3 Received: 7 November 2019 / Accepted: 2 April 2020 © Società Italiana di Medicina Interna (SIMI) 2020
Dear Editor, Dysnatremia, derangement in serum sodium concentration ([Na+]) is a common electrolyte disturbance in clinical practice [1]. During its treatment, [Na+] needs to be corrected slowly, since its rapid correction may cause severe brain damage [1]. Hence, availability of timely and reliable results of [Na+] influences the prognosis in dysnatremia. Blood gas analyzers (BGAs), which are used at a patient’s point of care location, can provide [ Na+] timelier than serum chemistry analyzers (SCAs), which are used in the hospital central laboratory. In addition, BGAs, which use the direct ion-selective-electrode method (ISEM), are assumed to measure [Na+] more reliably than SCAs, which use the indirect ISEM; the pre-analytical sample dilution in the indirect ISEM will increase variation in the measurement [2]. In this report, the variation was examined. The [Na+] in a certified Ringer’s solution containing 131 mmol/L sodium (SOLACET D, Terumo Corporation, Tokyo, Japan), in a certified normal saline (NS) solution containing 154 mmol/L sodium (Hikari Pharmaceutical CO., LTD. Tokyo, Japan), and in 2 serum samples was measured by using an SCA, the TBA-c8000 analyzer (Cannon Medical Systems, Tochigi, Japan), and a BGA, the GEM premier 4000 analyzer (Instrumentation Laboratory Company, MA, USA). The SCA measurement was performed as the following: twice a day before and after its manual calibration for 7 days in the Ringer’s solution, once a day before the * Masayuki Tanemoto mtanemoto‑[email protected] 1
Division of Nephrology, Department of Internal Medicine, International University of Health and Welfare School of Medicine, 13‑1 Higashi‑Kaigan‑Cho, Atami, Shizuoka 413‑8790, Japan
2
Dialysis Unit, Shin-Kuki General Hospital, Saitama, Japan
3
Central Laboratory Unit, Shin-Kuki General Hospital, Saitama, Japan
calibration for 5 days in the NS solution, and twice a day for 3 days in the serum samples. The BGA measurement was performed as the following: once a day for 7 days in the Ringer’s solution, once a day for 5 days in the NS solution, and twice a day for 3 days in the serum samples. Data presented by the devices in mmol/L were rounded to the nearest whole number. The difference between the measured [Na+] and the prepared concentration (∆[Na+]) was calculated by subtracting 131 and 154 from the measured [ Na+] in the Ringer’s solution and in the NS solution, respectively. Variables were reported as the range with the median and inter-quartile range (IQR). Figure 1 presents ∆[Na+] in the electrolyte solutions. In the Ringer’s solution, the ∆[Na+] of the BGA measurement ranged from − 5 to 7 (median 4, IQR 3 ~ 5) mmol/L, and that of the SCA measurement ranged from − 6 to − 2 (median − 4, IQR − 5 ~ −
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