Lithium Blood Level Test: Uses, Ranges, Side Effects

What Is the Lithium Blood Level Test?

Lithium is a mood stabiliser commonly prescribed for bipolar disorder. In my clinical practice, I often tell patients that this simple blood test is the cornerstone of safe and effective lithium therapy. It measures the amount of lithium in your blood, usually drawn as a trough level—just before your next dose—to ensure you're in the therapeutic window.

The test is essential because lithium has a narrow therapeutic index: too little won't control mood swings, and too much can be toxic. By monitoring regularly, we strike a balance that keeps you stable and safe.

Why Is Lithium Blood Level Monitored?

Preventing Toxicity While Ensuring Efficacy

Lithium levels can fluctuate due to hydration, kidney function, diet, and drug interactions. I've seen patients whose levels spike after a bout of vomiting or a salty meal. That's why we check levels every 3–6 months in stable patients, and more often when starting or adjusting the dose.

Monitoring Kidney and Thyroid Function

Long-term lithium use can affect the kidneys and thyroid. The blood level test is paired with renal and thyroid panels to catch early changes. My patients appreciate knowing that this surveillance keeps them one step ahead of complications.

What Is the Therapeutic Range for Lithium?

The target concentration depends on the condition being treated. For maintenance therapy in bipolar disorder, most guidelines recommend a trough level between 0.6 and 1.2 mmol/L. For acute mania, we may aim slightly higher (0.8–1.5 mmol/L) but only temporarily.

What Happens If Lithium Levels Are Too High?

Early signs of lithium toxicity include nausea, vomiting, diarrhoea, drowsiness, and a fine tremor. At higher levels (above 1.5 mmol/L), confusion, slurred speech, and muscle twitching appear. Levels above 2.0 mmol/L can lead to seizures, coma, or permanent kidney damage. If you experience any of these symptoms, stop the medication and seek urgent medical attention.

Lithium During Pregnancy

Pregnancy changes how the body handles lithium. Blood volume increases and kidney clearance alters, so levels can drop unexpectedly. We monitor more frequently—often every month—and adjust the dose to keep both mother and baby safe. Lithium has been linked to a small risk of Ebstein's anomaly in the first trimester, so preconception counselling is crucial.

How to Prepare for a Lithium Blood Test

To get an accurate trough level, the blood draw should be performed exactly 12 hours after your last dose. I advise patients to take their evening dose as usual, then come in the next morning before taking the morning pill. Stay well hydrated, avoid extreme salt changes, and let your doctor know about any new medications (including over-the-counter painkillers like ibuprofen, which can raise lithium levels).

Factors Affecting Lithium Levels

Many things can alter your lithium level: dehydration, sweating from exercise or fever, a low-salt diet, kidney problems, and interactions with ACE inhibitors, diuretics, or NSAIDs. Even caffeine and alcohol can have subtle effects. That's why I tell my patients, 'Don't make sudden changes to your diet or fluid intake without letting me know.'

How Often Should You Be Tested?

After starting lithium, we check levels every 1–2 weeks until stable. Once you're on a steady dose and your mood is controlled, testing every 3–6 months is standard. If you have kidney disease, are elderly, or take interacting medications, we test more often. Always carry a lithium card with your current dose and last level—it can be life-saving in an emergency.