DEAR DR. DONOHUE: Our daughter paid us a visit last year. During her stay she became sick. A large red spot appeared on her leg, and it grew in size. Lyme disease was suspected. When she returned to her home, blood tests indicated that she could have the disease, and she was treated with antibiotics. We would like to know more about Lyme disease and its treatment. – S.H.

ANSWER: Lyme disease is an infection that peaks in the warm months, when the tick population is at its height. Ticks carry the germ that causes it.

Three to 32 days following the bite of an infected tick, people break out with a circular spot (or spots) that has a red border that keeps enlarging. The center of the spot generally turns pale. In addition to the rash, people feel exhausted and often have headaches and a rise in temperature. They can also experience joint and muscle pain.

Those symptoms lessen, but weeks to months later, a new set of symptoms appears. One side of the face might droop, and the eye on that side stays opened. That condition is Bell’s palsy, and it is one manifestation of the second stage of Lyme disease. Other nerve troubles are more common. In addition, the heart can become inflamed, and it might develop irregular beats. The rash seen in the first stage can come back.

The third stage of Lyme disease occurs weeks to years after the second stage, and its salient symptom is painful, swollen joints — arthritis.

Lyme disease does not follow this script in all instances. One or two of the above symptoms might be its only signs.

Blood tests for Lyme disease must be interpreted with caution. They can be falsely positive or falsely negative. Two different tests should be done before declaring a diagnosis of Lyme disease.

Early antibiotic treatment can usually bring a cure. Some must contend with it for long stretches.

DEAR DR. DONOHUE: I have been told that a free-PSA test is a better test for prostate cancer than the regular PSA test. I’ve never heard of this test. Will you please tell me about it? – W.S.

ANSWER: The PSA test (prostate-specific antigen) is a widely used test for detection of prostate cancer. In most labs, PSA values below 4 ng/mL are considered normal. Values greater than 10 suggest prostate cancer. Numbers between 4 and 10 are in a no man’s land.

The free-PSA test can shed light on the ambiguous results in the 4 to 10 zone.

“Free” indicates blood PSA that is not glued to blood proteins. When the free PSA is higher than 25 percent, the probability of prostate cancer is not great. Low free-PSA numbers – those less than 10 percent – are suggestive of cancer. As you can see, that still leaves men whose values lie between 10 and 25 in a gray zone.

Free PSA provides information that the regular PSA test does not. But it is not a perfect test. Doctors are working to find the perfect test. In the meantime, we have to struggle with the available tests to predict the presence of prostate cancer.

DEAR DR. DONOHUE: I will really appreciate your writing a statement about human gestation. I read in an encyclopedia that human gestation takes 267 days or approximately 9 months. Two hundred and sixty-seven divided by 30 or 31 is less than nine months. What is the truth? – M.G.

ANSWER: Let me give you the numbers used in two prominent textbooks of obstetrics. A normal pregnancy lasts 280 to 281 days. If you consider that an average month has 31 days, then the division yields nine months — the commonly quoted length of a pregnancy.

No one can predict the length of an individual woman’s pregnancy. Pregnancy does not follow a strict timetable.

When a doctor estimates a woman’s date of delivery, the actual delivery date can fall two weeks before to two weeks after the estimated date.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475.