Stability of i-Stat EC6+ Cartridges: Effect of Storage Temperature on Shelf Life

Point-of-care testing is a valuable tool in many settings, including remote environments (1). The i-STAT Portable Clinical Blood Analyzer (i-STAT Corp.) has been tested extensively and has been used during spaceflight as both a research (2)(3) and a clinical(4) tool. One disadvantage of the Portable Clinical Blood Analyzer is the requirement for refrigerated storage for consumables (ambient storage is limited to 2 weeks). The effects of re-refrigeration after transient ambient storage are undocumented, but this is discouraged by the manufacturer.We determined the effects of long-term ambient storage and the effects of re-refrigeration on the performance of i-STAT EC6+ cartridges. Cartridges were stored under one of three treatment conditions: controlled temperature (refrigerated; 2–8 °C), room temperature (18–25 °C), or re-refrigerated. The re-refrigerated cartridges started the study at room temperature and were placed in the refrigerator after a specified number of days. For example, cartridges in the re-refrigerated 16-day group were held at room temperature for 16 days and then were placed in the refrigerator. Subsets were analyzed on study day 23, and after 1 month, 2 months, and so forth.We used two levels of aqueous controls (Bionostics Corp.) and two levels of blood controls (Hematronix). Each group consisted of 20 cartridges: 6 Bionostics level 1 controls, 6 Bionostics level 3, 4 Hematronix low controls, and 4 Hematronix high controls. Cartridges and aqueous controls were single lots; blood controls were from three lots (expiration constraints). The limit ranges (levels 1 and 3, respectively) of each lot of each control (from package inserts) were as follows: pH, 7.130–7.230 and 7.647–7.747; ionized calcium (iCa), 1.47–1.69 and 0.71–0.87 mmol/L; glucose, 2.2–3.2 and 13.4–19.8 mmol/L; sodium, 116–124 and 156–166 mmol/L; and potassium, 2.0–2.8 and 5.8–6.8 mmol/L. The overall hematocrit control limit range was 26–30% packed cell volume (PCV) for the …