Abstract
PURPOSE: Lithium (Li) is a well-established drug for the treatment of bipolar affective disorders.
Li as a drug is known to possess a narrow therapeutic index. Thus, regular monitoring
of blood Li in patients receiving Li therapy is essential. Plain tubes with clot activator
are known to interfere with Li estimation. The current study was planned to compare
Li estimation in sera from vacutainers with clot activator, and plasma from sodium
heparinized vacutainers with that of Li estimation in sera from glass vials. The time-dependant
stability of Li estimation on storage at 2°C–8°C for 48 h in these three set of tubes
was also evaluated.
MATERIALS AND METHODS: Blood from the patients on Li therapy (n = 100) was collected in 3 different collection tubes: plain vacutainer with clot
activator (S), Sodium heparinized vacutainer (P) and Glass vial (G) and was analyzed
by ion selective electrode (ISE) analyzer for Li levels. Secondary aliquots were also
taken from each type of collection tube and stored at 2°C–8°C. Time-dependant stability
of Li estimation was checked at 12 h, 24 h, and 48 h. ANOVA followed by Tukey's posttest
was performed to calculate statistical significance taking glass vial as reference
collection tube. Bland–Altman plots were plotted to compare between three collection
tubes at baseline. Stability on storage was defined when >95% of the samples were
within allowable error limit for that time point taking baseline levels as reference.
RESULTS: A mean bias of 0.18 mmol/L and mean percentage bias of 19.9% in Li levels was observed
between serum from (S) than serum from (G). This difference was found to be statistically
significant. However, statistically nonsignificant mean bias of 0.02 mmol/L and mean
percentage bias of 3.34% in Li levels was observed between plasma from (P) and serum
from (G). Time-dependant stability was observed more in glass vials as compared to
vacutainers with clot activator or sodium heparin.
CONCLUSION: Serum from glass vial should be the preferred method for blood collection to determine
Li levels.
Key words
Bipolar disorder - ion selective electrode analyser - lithium
