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CASE REPORT |
From the California Poison Control System San Diego, Division of Medical Toxicology, University of California, San Diego, San Diego, CA.
Address reprint requests to: Sean Patrick Nordt, PharmD, ABAT, California Poison Control System San Diego, Division of Medical Toxicology, University of California, San Diego, 200 West Arbor Dr., San Diego, CA 92103-8925. Email: snordt{at}ucsd.edu
ABSTRACT
INTRODUCTION: We present the case of a minimally symptomatic patient found to have an elevated lithium level after a blood sample was inadvertently obtained in a green-top tube containing lithium heparin.
CASE REPORT: A 33-year-old woman presented 8 hours after ingesting an unknown quantity of sustained-release lithium carbonate, venlafaxine, clonazepam, and valproic acid. The patient was noted to be slightly drowsy but could be easily aroused. No gastrointestinal symptoms or electrocardiographic changes were observed. The patient was admitted to the intensive care unit for observation. The patient’s lithium level 21 hours after ingestion was 5.6 mEq/liter, but she was clinically asymptomatic. The disagreement between symptoms and lithium level led to the discovery that this blood sample had been collected in a lithium heparin tube, thereby falsely elevating the level.
CONCLUSIONS: This case illustrates the wisdom of the old adage to "treat the patient, not the levels." Caution should be used by physicians, nurses, technicians, and other personnel when obtaining blood samples.
Key Words: lithium • poisoning • laboratory error
Lithium toxicity still remains a common occurrence (1). The hallmark symptoms of acute lithium poisoning include severe neurologic and gastrointestinal symptoms. Classically, nystagmus, ataxia, tremors, nausea, vomiting, and diarrhea are seen. Patients may progress to coma, but death rarely occurs, even after large ingestions (1, 2). We present a case of an elevated lithium level in a patient who had minimal symptoms after a blood sample was inadvertently drawn in a green-top collection tube preserved with lithium heparin.
CASE REPORT
A 33-year-old woman presented to the emergency department 8 hours after ingesting an unknown quantity of venlafaxine, clonazepam, valproic acid, and sustained-release lithium carbonate (Eskalith CR). The patient was alert and orientated and had a heart rate of 70 bpm and a systolic blood pressure of 130 mm Hg. A single dose of activated charcoal was administered orally. A 12-lead electrocardiogram did not reveal any abnormalities. Initial electrolyte levels were as follows: sodium, 140 mEq/liter; potassium, 3.1 mEq/liter; chloride, 106 mEq/liter; bicarbonate, 24 mEq/liter; blood urea nitrogen, 24 mg/dl; creatinine, 1.1 mg/dl; and glucose, 83 mg/dl. The initial lithium level was 2.7 mEq/liter, and the valproate concentration was 93 mg/liter. An intravenous infusion of normal saline with 20 mEq/liter potassium chloride was initiated. The second lithium level, obtained approximately 2 hours later, revealed an increase in the lithium level to 3.1 mEq/liter. The patient was noted to be slightly drowsy but could be easily aroused. She was treated supportively and had no symptoms other than drowsiness. The patient’s serum sodium level was 144 mEq/liter; potassium, 2.1 mEq/liter; blood urea nitrogen, 6 mg/dl; and creatinine, 0.8 mg/dl. The patient was admitted to the intensive care unit for observation. A third lithium level, obtained 16 hours after ingestion, was 3.6 mEq/liter. The patient had no gastrointestinal symptoms or electrocardiographic changes. Intravenous hydration was continued. A fourth lithium level, obtained 21 hours after ingestion, was 5.6 mEq/liter; however, the patient was clinically asymptomatic. Because of the disagreement between the elevated lithium level and the absence of any clinical symptoms, a laboratory error was suspected. It was then realized that the fourth blood sample had been inadvertently drawn in a green-top collection tube containing lithium heparin as a preservative. A fifth sample was drawn 25 hours after ingestion and demonstrated a lithium level of 2.2 mEq/liter. The patient remained asymptomatic. No gastrointestinal symptoms were noted. The only clinical manifestation noted during the patient’s admission was slight drowsiness, which resolved over the first 10 hours of admission.
DISCUSSION
Lithium has been used for many years in the treatment of bipolar disorder. Historically, lithium has been used to induce leukocytosis in neutropenic patients and as a salt substitute (3–5). Lithium carbonate is the most commonly used salt form because of its larger content of elemental lithium (3). Many of the lithium carbonate products available are sustained-release products (e. g., Eskalith CR and Lithobid), which may prolong the duration of symptoms.
The most commonly reported symptoms with supratherapeutic levels include both gastrointestinal and neurologic complaints (4, 6). Nausea, vomiting, and diarrhea may be seen with dosages at the higher end of the therapeutic range and increase in severity as lithium levels increase. Central nervous system effects include somnolence, ataxia, nystagmus, and confusion (5–7). These patients may become comatose (1, 2). Many patients with lithium toxicity will exhibit a fine resting tremor, although this can also be seen at therapeutic levels. Severe cardiotoxic effects are rarely observed, although nonspecific, clinically insignificant electrocardiographic changes may be seen (eg, T-wave inversion, ST-segment depression, or prolongation of the QT interval) (3, 4, 8). The patient in this case report had also ingested other substances; therefore, it is possible that some of the clinical manifestations of lithium poisoning may have been masked.
Gastric lavage is rarely of any benefit more than 60 minutes after ingestion and is further complicated by the large diameter of the various dosage forms of lithium (eg, sustained-release tablets) (9). In addition, lithium poisoning is often accompanied by gastrointestinal symptoms, such as vomiting. Whole-bowel irrigation with GoLytely (polyethylene glycol 3350) has been used to remove many different sustained-release medications after large, acute ingestions (2, 10). Whole-bowel irrigation was not performed in our patient because of her delayed presentation. More recently, the administration of an ion exchange resin, sodium polystyrene, has been used with varied success (1, 11). Limitations of sodium polystyrene include the requirement of relatively large dosages and potential hypokalemia (11). Because of limited plasma protein binding and low molecular weight, hemodialysis rapidly removes lithium from the bloodstream, giving a false impression of the drug being removed as serum levels decrease. Unfortunately, hemodialysis is inefficient at removing lithium. This is further complicated by a posthemodialysis redistribution phenomenon, in which serum levels approach predialysis levels 6 to 8 hours after dialysis and may require redialysis (1, 6, 7, 12).
A laboratory error was suspected in this case because the patient had an extremely high lithium level (5.6 mEq/liter) but only mild clinical symptoms. The patient’s fourth sample was drawn in a green-top tube containing lithium heparin, which falsely increased the lithium level. Lithium heparin blood collection tubes (7 ml) contain 14.3 USP standard units of lithium heparin (13). We were able to identify only one previous report of an elevated lithium level after inadvertent collection of the sample in a tube preserved with lithium heparin (13). These authors reported lithium levels of 1.2 to 2.0 mEq/liter (mean, 1.5 mEq/liter) in blood samples of adult volunteers not taking lithium that were collected in green-top tubes (13). Lithium serum samples should be collected in a red-top tube containing no anticoagulants.
CONCLUSION
We present the case of a minimally symptomatic patient with an apparently elevated lithium level after a blood sample was inadvertently collected in a green-top tube containing lithium heparin. This case illustrates the wisdom of the old adage to "treat the patient, not the levels." Without clinical correlation, this patient may have had to undergo hemodialysis on the basis of lithium level alone. The laboratory should be consulted if there are any questions about which tube to use to obtain a blood sample.
Received for publication January 29, 1999.
Accepted for publication April 29, 1999.
REFERENCES
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