Short-term Effects of Lithium on White Blood Cell Counts and on Levels of Serum Thyroid-stimulating Hormone and Creatinine in Adolescent Inpatients: a Retrospective Naturalistic Study

Objective: The purpose of this study was to determine if the known side effects of lithium in adults may be generalized to younger patients with psychiatric disorders.

Methods: A retrospective naturalistic study design was used. Data were collected from the database of a tertiary pediatric medical center covering the years 1994-2010. Included were patients hospitalized for bipolar and non-bipolar disorders and treated with lithium, alone or in combination with other medications. The electronic medical files were reviewed for changes in thyroid and kidney function and for hematological parameters during the course of treatment.

Results: Sixty-one patients 12.5-20.4 years of age (mean 16.94±1.66) met the study criteria: 33 with bipolar disorder and 28 with a non-bipolar disorder. Mean duration of lithium treatment (mean lithium blood level, 0.73±0.24 mEq/L) was 193.68±254.35 days. Mean levels of thyroid-stimulating hormones (TSH) rose significantly from baseline to last measurement (3.16±2.68 vs. 1.52±0.92 mU/L; paired t=-5.19, df=50, p<0.001); in 25% of patients, TSH levels at the last measurement were above normal (≥4 mU/L). Only one patient developed TSH values >10 mU/L (the threshold considered clinically significant). Positive correlation was found between pre- and posttreatment TSH levels (Pearson's r=0.60; n=51, p<0.05). White blood cell count (WBC) also increased significantly following lithium treatment (7195±2151 vs. 7944±2096 cells/mm(3); t=2.83, df=60, p=0.006). No significant changes were noted in serum creatinine levels. There was no difference in these parameters between patients treated with lithium alone or in combination with other medications.

Conclusions: Lithium treatment in adolescents with bipolar or non-bipolar disorders is associated with a significant increase in blood TSH levels and WBC count. Lithium-treated adolescent inpatients with a high basal TSH level may be at risk of developing pituitary-thyroid axis dysregulation. Therefore, baseline measurement of thyroid functions and serial monitoring throughout treatment are recommended.