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Dear Dr. Roach, I recently heard someone say that he had had an anaphylactic reaction to a vaccine several hours after administration, for example 14 hours later. Can anaphylaxis actually occur long after exposure to an allergen? This is a general question, not specific to a vaccine. I've always had the impression that a reaction like this is happening much more quickly.
A F.
Anaphylaxis is a serious life-threatening allergic reaction. It is rare. Less than two percent of people will be anaphylactic during their lifetime. This can happen because of medications, such as immunotherapy against allergies, and less frequently because of other drugs, especially those that are injected, including vaccines. This can also happen because of foods, including legumes (peanuts) and nuts.
Anaphylaxis usually occurs within minutes, rarely until one hour after exposure. It is treated with epinephrine (also called adrenaline) to counteract the collapse of the circulatory system that is part of the reaction.
About 20% of people with anaphylaxis will have a second set of symptoms once the initial symptoms have been successfully treated.
These can be avoided, to a certain extent, with the use of steroids. Therefore, anyone with anaphylaxis should be evaluated immediately, even if they have successfully treated with an epinephrine injection.
The second set of symptoms occurs most often within three hours, but cases that may occur 10 hours later have been described.
In the case you are describing, it is possible that the initial symptoms were treated and that the person noticed a second series, although 14 hours were longer than those reported.
Dear Dr. Roach, I had half of my thyroid removed many years ago and I am taking 37.5 mcg of Synthroid since. My last TSH test is 1.28. Even if it is in the normal range, I wonder if it is too low for me, because I have little energy, even for an 88 year old man. But higher doses cause an essential tremor.
HA.
Experienced clinicians know that sometimes it is necessary to individualize thyroid hormone replacement doses and that, in some people, the result obtained may not be optimal, even if it lies in the limits of normal.
On the other hand, too much thyroid hormone is bad for bones; in your case, bad for your tremor; and perhaps the most disturbing, bad for your heart. A thyroid replacement dose too high and you risk developing atrial fibrillation.
Thyroid tests have many moving parts.
T4, also called thyroxine, is converted to T3, triiodothyronine, which is the active thyroid hormone.
FTI, the free thyroxine index, adjusts the level of thyroid hormone to proteins that bind to thyroid hormone). The higher the T3, T4 and FTI, the more thyroid hormone you have.
TSH does not measure the thyroid hormone.
The thyroid stimulating hormone is manufactured by the pituitary gland and, in almost all cases, the higher the TSH is, the lower the level of thyroid hormone is because the pituitary gland produces more of TSH if the body detects that the level of thyroid hormone is too low.
The only exception is the brain producing too much TSH, which is usually due to a tumor.
In the laboratory of my hospital, a normal rate of TSH is between 0.5 and 4.
This would mean that you do not have a lot of leeway to increase your thyroid dose without having a really high level, with its risks.
Finally, a small minority of people have difficulty converting T4 into active T3. The addition of a small dose of T3 or the use of a combination of T4 / T3 preparations has improved the symptoms of some people without a clear increase in thyroid hormone dose.
Dr. Roach regretted that he could not reply to individual letters, but would incorporate them in the column whenever possible. Readers can send questions via email to [email protected].
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