Blood test not always needed to regulate meds dose

DEAR DR. ROACH: My son was diagnosed with obsessive compulsive disorder. The doctor prescribed sertraline (Zoloft). When I inquired about a blood test to determine his serotonin levels, the doctor told me it wasn’t necessary. How could a medication be prescribed without knowing what his levels are? My wife has her levels checked each year for her thyroid medication. – M.M.

ANSWER: There are some medications whose effectiveness can be followed using blood tests, and a few that must be. If a medication is being used to treat a symptom, it usually is more important to treat the symptom than to treat a number so sometimes experienced clinicians will use a dose that causes the blood level to be a bit higher or lower than recommended. On the other hand, some medicines – for instance, warfarin to prevent blood clotting – need to be precisely regulated using blood testing to be sure it is both effective and nontoxic.

In the case of sertraline and other selective serotonin reuptake inhibitors, there isn’t a blood test to be followed. It’s not serotonin in the blood that is affected by these medications, but serotonin in the synapses (the connections between brain cells). SSRIs block the clearing of serotonin after it is released, allowing the nerve to increase the rate of firing.

The dose of sertraline depends on the condition treated. Smaller doses are needed for anxiety or depression than usually are needed for obsessive compulsive disorder. Fortunately, sertraline is fairly safe: Even the higher doses needed for OCD generally have few side effects. Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or request an order form of available health newsletters at 628 Virginia Dr., Orlando, Fla., 32803. Health newsletters may be ordered from www.rbmamall.com.