Antigens after COVID remain in system, but they aren’t infectious

Dear Dr. Roach: Will I continue to test positive for COVID-19 antigens even after I recover from the virus? I tested positive using the free, at-home COVID-19 antigen self-test a week ago, and I tested positive again yesterday. Once you have the antigens in your system, don’t they stay there for a while? — R.L.M.

Dear R.L.M.: It is frequent that people will have persistently positive COVID-19 tests after infection, sometimes for weeks, but that does not mean that they are still infectious. It is quite rare for a person with a normal immune system and mild or moderate disease to continue to be infectious more than 10 days after the onset of infection. People who have had severe disease (such as those who required inpatient hospitalization with a ventilator) or those with severe immune system disease (such as those taking cancer chemotherapy or other powerful drugs to suppress the immune system) may continue to be infectious 20 or more days after infection and should consult an expert for information on duration of isolation.

Dear Dr. Roach: I have low sodium levels running between 128 and 131 mEq/L for several years. I was on hydrochlorothiazide for many years, but I was taken off some time ago. My sodium remained low. I don’t feel like I drink an excess of water. Should I be concerned, and is there anything I can do to improve my numbers? — S.H.

Dear S.H.: A normal sodium level in the blood is between 135 and 145 mEq/L. You have a slightly low sodium level, which is common. There are many different causes. Diuretics, like hydrochlorothiazide, is a common one, but you are no longer on that. One condition that physicians are frequently concerned about is the syndrome of inappropriate anti-diuretic hormone secretion. In this condition (SIADH), a hormone called antidiuretic hormone, or arginine vasopressin, is secreted all the time, causing the urine to be too concentrated and the sodium level to be too high. The problem is really about water, not salt; therefore, water restriction is the primary treatment when the diagnosis is SIADH.

The brain has an area responsible for maintaining sodium levels (called the “osmostat”). One possibility is that the years you spent on hydrochlorothiazide “reset” your osmostat to this slightly lower sodium level. At a level of around 130, I wouldn’t expect you to have symptoms, and you haven’t mentioned any, so you may not need any treatment at all. Still, some people who seem to have no symptoms with a sodium level of less than 130 can have subtle improvements in brain functioning if the level is above 130, and at least one study showed a reduction in falls among people whose low sodium levels are corrected. You are already right about the goal for treatment of low sodium levels.

You should talk to your regular doctor about whether you need treatment and whether some moderate fluid restriction is the right treatment for you. A kidney specialist is the expert in diagnosis and management of SIADH and a reset for the osmostat.