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Quest Diagnostics Quest Diagnostics

Lithium

Blood
Optimal Result: 0.6 - 1.2 mmol/L.

Lithium Blood Test – What It Measures and Why It Matters

This test measures the amount of lithium in your blood to help manage treatment for mood disorders like bipolar disorder. Lithium is a naturally occurring element used as a mood stabilizer, especially for controlling mania and preventing mood swings. Because lithium has a very narrow therapeutic range, levels must be carefully monitored to ensure the dose is effective—not too low (ineffective) and not too high (toxic).

Why This Test Is Done

Monitoring lithium levels helps:

  • Ensure treatment for bipolar disorder is working

  • Adjust dosage safely

  • Prevent lithium toxicity, which can be dangerous

Your doctor may order this test if you're taking lithium and experiencing symptoms like:

  • Fatigue or drowsiness

  • Dizziness or confusion

  • Muscle weakness or tremors

  • Nausea, vomiting, or diarrhea

  • Slurred speech or lack of coordination

  • Unusual restlessness

How Lithium Works in the Body

  • Lithium is fully absorbed within 6–8 hours after oral intake.

  • Its effects may take 5–10 days to become noticeable.

  • The drug is processed almost entirely by the kidneys, and its half-life (how long it stays in your body) ranges from 17 to 36 hours.

  • Lithium is distributed in total body water and accumulates differently in various tissues, including the brain.

  • In steady state, cerebrospinal fluid levels are about 40% of serum levels.

  • Lithium is not protein-bound, meaning it moves freely in the body.

What Affects Lithium Levels

  • Sodium balance: Low sodium levels can cause the body to retain lithium, while high sodium levels increase its excretion. Regular plasma sodium checks are recommended.

  • Kidney function: Since lithium is cleared by the kidneys, variations in kidney health can affect blood levels.

  • Intracellular activity: Lithium acts inside cells, so red blood cell (erythrocyte) levels may better reflect its activity than serum levels in some patients.

Side Effects and Long-Term Considerations

  • Digestive symptoms (nausea, vomiting, diarrhea) can happen at any stage and at any serum level.

  • Nephrogenic diabetes insipidus (a kidney-related condition affecting water balance) occurs in about 33% of patients.

  • Thyroid effects: Lithium can slightly lower thyroid hormone (T4) levels and raise TSH levels. About 4% of patients may develop goiter or hypothyroidism.

  • These effects are often manageable with dose adjustments or additional treatment.

Key Takeaway

Because of its narrow therapeutic window, lithium therapy requires regular blood tests to balance effectiveness with safety. Always follow your doctor’s instructions for timing your dose and test, and report any unusual symptoms. With proper monitoring, lithium can be a highly effective treatment for mood stabilization.

References:

  • Gelenberg AJ et al. N Engl J Med. 1989;321(22):1489–1493. PMID: 2811970

  • American Medical Association, Drug Evaluations Subscription, 1992.

What does it mean if your Lithium result is too high?

Intoxication never occurs suddenly. Several days to a week before full-blown symptoms develop, a patient will experience lethargy, drowsiness, tremor, muscle twitching, dysarthria, anorexia and vomiting or diarrhea. A fully developed case of intoxication shows coma to semicoma, rigidity, hyperactive reflexes and seizures at times. There is a high incidence of pulmonary complications.

What does it mean if your Lithium result is too low?

Low Lithium Levels – What It Means and What to Do

What does a low lithium level mean?
Low blood levels of lithium typically mean the medication is not at a high enough level in your body to be effective. This can reduce its ability to manage conditions like bipolar disorder, mania, or as an add-on for depression. Lithium needs to stay within a specific therapeutic range (usually 0.6–1.2 mmol/L) to work properly and safely.

Common Reasons for Low Lithium Levels

  • Missed or irregular doses

  • Starting lithium recently or having a recent dose change

  • Fast kidney clearance (some people naturally eliminate it faster)

  • Drug interactions (like with caffeine, certain diuretics, or NSAIDs)

  • Too much or too little fluid intake (affects lithium balance)

  • Malabsorption issues (e.g., GI conditions that affect absorption)

Why It Matters

If your lithium level is too low, it may not provide its full mood-stabilizing benefits. This can increase the risk of relapse, mood swings, or worsening symptoms. Regular blood tests are important to make sure your level stays in the right zone—not too low, and not too high.

What to Do Next

  • Talk to your doctor: They may adjust your dose or repeat the test in a few days.

  • Check the timing: Lithium blood tests should be done 12 hours after your last dose. Testing too early can give a falsely low reading.

  • Take your medication consistently: Same time every day, no skipped doses.

  • Mention all medications: Let your doctor know if you're taking any new prescriptions, over-the-counter drugs, or supplements—these can impact lithium levels.

  • Stay hydrated: Drink a steady, moderate amount of water daily. Avoid extremes.

Bottom Line

Low lithium levels are common and often easy to fix with a dose adjustment or lifestyle tweaks. Always follow your doctor’s guidance and tell them if your mood changes or if you notice any side effects. Keeping your lithium in the right range is key to staying well.

Frequently asked questions

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