Dear Doctor: I had a coronavirus test, and it was negative. Then I had the antibody test, and I was surprised when it came back positive because I hadn’t been sick. How do these coronavirus tests work? Are they accurate?

Dear Reader: There are two testing goals related to SARS-CoV-2, the coronavirus that causes COVID-19. One is to learn whether or not you are currently infected. The other is to see whether or not you have been infected in the past.

By far, the most common test being conducted at this time is for the coronavirus itself. This involves the use of a nasal swab, which is a long, thin stick with soft brushlike material on the tip. The swab is carefully inserted deep into the nose, to the passageway that connects to the back of the throat. (It’s uncomfortable, but not painful.) The goal is to gather a sample that includes cells and secretions from the back of the throat and from all along the length of the nose. Although there’s a less-invasive COVID-19 test that relies on just a throat swab, similar to the test used for strep throat, it’s not considered to be as accurate as the nasal swab. A newly developed saliva test, which requires just a sample of spit and returns a result within 30 minutes, has been submitted for regulatory review. Each of these tests look for genetic markers specific to SARS-CoV-2. Meanwhile, on July 3, the Centers for Disease Control and Prevention announced the development of a single test able to diagnose influenzas A and B as well as the novel coronavirus.

When you become sick with a virus, the immune system sends specialized proteins known as antibodies to mount an attack. Since antibodies are specific to the invader they are fighting, it’s often possible to identify when someone’s immune system has fought off a particular pathogen. It usually takes at least one week, and can take up to three weeks or longer, for the body to develop antibodies. Although it’s rare, despite being infected by a pathogen, some people don’t develop antibodies at all.

An antibody test is performed by screening a blood sample for specific markers of the antibody in question. Unfortunately, in the case of the novel coronavirus, the accuracy of these tests is in question. The CDC has found that up to half of antibody test results may be inaccurate, giving either a false positive or a false negative. A recent study examined 40 different types of antibody tests and found a wide disparity in their accuracy. The researchers suggested that until these tests are improved, people should not rely on the results.

As for having antibodies to SARS-CoV-2 despite not having been physically ill, that’s entirely possible. A hallmark of this virus is that some people, despite being infected, don’t develop symptoms. However, they can still pass along the virus, which is known as asymptomatic transmission. That’s why, in order to protect the people around us, it’s so important for each of us to wear a face covering in public, social distance and wash our hands.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My 36-year-old son has recently been diagnosed with primary lymphedema. He has developed open wounds on both of his legs and is in a lot of pain. The condition limits his movement, and he has become depressed. Can you provide information about treatment, and where to seek it?

Dear Reader: Lymphedema is chronic and progressive swelling that occurs because the lymphatic system, which is part of the immune system, isn’t working properly.

The lymphatic system is made up of a network of minute, thin-walled tubes known as lymphatic vessels, and by hundreds of lymph nodes, which work together to carry and filter lymph throughout the body. Lymph is a clear fluid, rich in white blood cells, which helps fight infection and transport waste, toxins and debris. If you’ve ever had a scrape and seen a clear, watery fluid seep out of the wound, that was lymph. Unlike the blood circulatory system, which uses the force of the heartbeat to propel blood, the lymph system is largely dependent on muscle movement to keep things flowing. When either the lymph vessels or the lymph nodes become damaged, lymph begins to back up in that part of the body and causes swelling.

Swelling that arises due to lymphatic injury or obstruction is called secondary lymphedema. It’s often seen in cancer patients whose treatment involved the surgical removal of lymph nodes. Swelling that occurs independent of surgery or other damage, as in your son’s case, is known as primary lymphedema. It’s a rare inherited condition in which the lymphatic vessels are not properly formed and can’t carry out their task.

There is no cure for lymphedema at this time. Instead, the focus is on managing the condition. This includes specialized massage to help with drainage, the use of compression garments, light exercise focusing on muscle contraction to encourage lymph movement, limb elevation and pneumatic compression.

An effective treatment approach known as complete decongestive therapy, or CDT, which originated in Europe and Australia, is now becoming popular in the U.S. It combines a number of lymphedema therapies into a comprehensive program that focuses on swelling reduction, maintenance and self-care. Although your son will benefit from lymphedema treatment, your first priority is helping him get appropriate wound care. Due to swelling and skin tension, patients with lymphedema are at high risk of having a nick or a scratch develop into an open wound. If there’s a wound clinic in your area, the health care providers there can initiate treatment and teach you and your son how to care for the wounds at home. Your family doctor can help as well.

Lymphedema is a complex and challenging condition, so it’s important to seek out someone with expertise in the condition. Most cancer centers and hospital-based cancer programs offer lymphedema support or therapy, and can often provide referrals. Two organizations, the National Lymphedema Network (NLN) and the Lymphology Association of North America (LANA), oversee certification programs for lymphedema therapists. They also offer excellent resources, including directories of therapists. You can find them at lymphnet.org and clt-lana.org.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My husband and I ate more junk food than usual during the coronavirus lockdown, and we both gained a few pounds. We’re trying for a healthier diet, with more fresh fruit and vegetables, but now I’m getting bloated after meals. What causes that? How can I make it stop?

Dear Reader: Whether it’s due to stress, boredom or simply experimenting in the kitchen to help pass the time, many people during the lockdown began taking in more fuel than their bodies were burning. At the same time, physical activities that had been hardwired into our daily routines were suddenly absent. Visits to the gym, the two-block walk from the parking space to the office, the staircase you choose rather than taking the elevator, those quick, darting runs as you chase a toddler through the park -- they all add up. For many, the increase in food and the loss of activity have resulted in what has been dubbed the “quarantine 15.” And as you have experienced, dietary changes to address the weight gain can lead to abdominal bloating.

Although bloating can be a symptom of gastrointestinal disorders, including irritable bowel syndrome, Crohn’s disease and ulcerative colitis, more often, the condition is associated with a buildup of excess gas in the digestive tract. Symptoms can include a feeling of fullness that causes discomfort or pain, and which can cause the stomach to become distended. This is often accompanied by an increase in belching or passing gas and rumbling sounds in the stomach or bowels. If bloating leads to nausea, diarrhea, fever or blood in the stool, it’s important to seek medical care.

One of the most common reasons for a sudden onset of bloating is a change to the diet. For people who are lactose intolerant, even a small amount of a dairy product can set off an episode. Unfortunately, many of the foods we turn to when cleaning up our diets are notorious for causing gas. Cauliflower, kale, broccoli, Brussels sprouts and other cruciferous vegetables contain a sugar known as raffinose. It gets digested by the bacteria in your gut, which produce gas as a byproduct of their meal. Beans, legumes and certain grains also contain indigestible fiber and sugars that feed our gut bacteria and earn us a bout of bloating.

With a bit of detective work in the form of an elimination diet, it’s possible to pinpoint the foods causing your episodes of bloating. Remove all suspect foods from your diet for a few days. Then, day by day, reintroduce one of the suspected culprits. You can then either skip the difficult food altogether, or reintroduce it very gradually and see if your body adjusts. Some people who can’t tolerate raw broccoli or kale find that breaking it down through cooking helps mitigate the aftereffects.

Carbonated beverages, eating too much or too quickly, and meals high in salt and fat can also contribute to bloating, so be aware of your behaviors as well. And if the bloating continues or gets worse, please check in with your doctor to eliminate other potential causes.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)