DEAR DR. ROACH: I am a 58-year-old male. Several months ago, I lost 17 pounds, and even though I have gained back about 2 pounds in the past month, I cannot gain the weight back, even by increasing my food intake. I feel tired all the time, and my energy level is not good. My doctor did a CBC, and my white blood cell count is low, at 3.1 (range is 4-11). He asked me if I recently had a cold, and I told him I had not. Since it was a new doctor, there are no previous results for comparison. The doctor did not tell me anything or instruct me to do anything else, which concerns me. There are two other results with low readings: lymphocytes are 0.1 (range is 1.2-3.4), and lymphocyte percent is 3.4 (range is 20-45).

I would like to know what, if anything, I should do next, other than waiting a few months for another blood test. Do I have to be worried about this? — V.B.

ANSWER: I am sorry, but you do have to be worried about this. Your lymphocyte count is extremely low. There are many potential causes, some of which are serious. Infections are the most common cause. Any serious infection can temporarily reduce lymphocyte count, but most of these are acute, to the point that people need hospitalization.

One common infection to cause a low lymphocyte count is HIV. In the early days of the epidemic, a low lymphocyte count was a clue to either acute or advanced HIV. The Centers for Disease Control and Prevention recommends, and I agree, that all adults should get an HIV test as a part of their routine checkups, and that people with ongoing risk should get a test annually.

A partial list of other causes for low lymphocyte count include medications (usually powerful anti-immune-system medicines or chemotherapy), autoimmune diseases such as lupus or rheumatoid arthritis, lymphoma and other cancers, and primary diseases of the immune system, such as aplastic anemia. Previous results would help indicate whether this is a new condition.

This can’t wait a few months for a follow-up test. If your doctor isn’t looking aggressively for the cause, you need a second opinion.

The arthritis booklet discusses rheumatoid arthritis, osteoarthritis and lupus. Readers can order a copy by writing: Dr. Roach — No. 301, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. ROACH: While reading your recent article about sulfites, a question came to mind: What are sulfites? Are they mineral, chemical, organic? Do they grow on trees? How do they affect food? — M.C.

ANSWER: Sulfites are chemicals found naturally at low levels in wine and some foods, and are used as preservatives at significantly higher levels.

Most people are not sensitive to sulfites even at high levels, but some people have significant reactions even at fairly low levels. People with severe allergies need to know that sulfites are not always indicated on the label and should educate themselves about all the foods containing sulfites. One resource I found is at https://edis.ifas.ufl.edu/fy731.

Everything we eat, drink and breathe is composed of chemicals. The difference between a “bad” chemical and a “good” one is one of dosage: We can’t live without oxygen, but too much oxygen is toxic. Most medications are useless at extremely low doses, helpful for some people with certain conditions at the proper dosage, and toxic if taken at too high a dose. Sulfites are no exception to this rule and, like any other chemical, some people are more sensitive to toxic effects at lower doses than others.

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 P.O. Box 536475, Orlando, FL 32853-6475. Health newsletters may be ordered from www.rbmamall.com.