Dietary citrate and plasma ionized calcium: Implications for platelet donors.

Background Platelet donors receive 40 mmol or more of IV citrate anion during donation. When plasma ionized calcium ([Ca2+]) falls by ∼20%, half of the donors report symptoms of hypocalcemic toxicity. Citrus juices contain clinically relevant amounts of citrate anion. We asked whether citrus juice can lower [Ca2+] thus potentially contributing to hypocalcemic toxicity. Method Six volunteers were given 20.4 mmol of citrate anion as grapefruit juice or orange juice. Capillary blood obtained by fingerstick was analyzed for [Ca2+] using an iSTAT point-of-care blood analyzer. [Ca2+] was measured at baseline and then 30, 60, 120, and 180 minutes after drinking juice. Subjects were tested with the alternative juice on a subsequent day. The outcome measure was the percent change in plasma [Ca2+] from baseline. Results [Ca2+] fell −2.2% to −11.5% in four of six subjects 30 minutes after drinking grapefruit juice. The effect persisted up to 3 hours. [Ca2+] fell −2.1% to −12.2% in four of six subjects 30-60 minutes after drinking orange juice. The effect abated after 2 hours. We could not correlate gender or body surface area to these findings. Summary and Conclusions: Citrus juice may lower [Ca2+] for 2-3 hours. This could add to the effect of IV citrate infusion during platelet donation, thus worsening the expected fall in [Ca2+]. This, in turn, would likely increase the rate and severity of hypocalcemic toxicity. It is prudent to advise platelet donors to avoid high citrate anion beverages, such as citrus juice, for at least 4 hours prior to donation.