July 8, 2020
Antibody Testing – What Is It Telling Us?
Many of you have come in for testing to see if you have antibodies to SARS-CoV-2 indicating a previously undiagnosed infection. Although this information isn’t that useful clinically (we do not yet know enough to say if antibodies are protective against reinfection and if so, for how long), we are following the seroprevalence of COVID-19 in our patient population at Wise Patient with interest. The CDC is also trying to learn more about the prevalence of the virus in communities using results of antibody tests. It is partnering with commercial laboratories and state departments of health to conduct a large-scale geographic seroprevalence survey based on unidentified serum samples from patients seeking care for reasons other than COVID-19. They have started with the health departments in 6 states and Washington, specifically Westernal Washington, was one of those first six. Between March 23 and April 1, 3,265 samples from commercial laboratories in King, Snohomish, Pierce, Kitsap and Grays Harbor Counties were collected. Based on these samples, the seroprevalence in these areas was 1.13%. If this represented the true seroprevalence in these counties at that time, there would have been 48,300 cases during that same time. In actuality, 4,300 patients tested positive for COVID-19 in these counties over that time frame. Based on this survey, the seroprevalence would be estimated at 11X higher than the number of diagnosed cases in that time frame.
If you are interested in following what antibody tests are telling us about the prevalence of the virus, you can follow the numbers as they come in from other states here:
Apprehension about Hypertension
This pandemic is a good excuse to start tracking your blood pressure.
Hypertension (high blood pressure) has been associated with worse outcomes in people with COVID-19 infections, but there has been some debate about whether these published observations have adequately adjusted for other conditions that are more often found in patients with hypertension (so-called confounding factors). A recent meta-analysis (a pooled statistical analysis of multiple studies on the same topic) prioritized studies with more thorough adjustment for confounding factors, and found that, yes, hypertension was significantly associated with increased risk of adverse outcomes in patients with COVID-19 (https://www.journalofinfection.com/article/S0163-4453(20)30441-2/pdf).
Association is not causation, to echo the medical epidemiology 101 professor. Yet, you aren’t going to see a study that randomizes people with hypertension to control their blood pressure vs. head-in-the-sand and watches what group gets sicker once infected with SARS-CoV-2. Fortunately, the argument for tracking and attempting to control most people’s hypertension was pretty sound before the pandemic, so we might as well begin with that:
Normal blood pressure:
- Systolic <120 mmHg and diastolic <80 mmHg
Mildly elevated blood pressure:
- Systolic 120 to 129 mmHg and diastolic <80 mmHg
- Stage 1 – Systolic 130 to 139 mmHg or diastolic 80 to 89 mmHg
- Stage 2 – Systolic at least 140 mmHg or diastolic at least 90 mmHg
If there is a disparity in category between the systolic and diastolic pressures, the higher value determines the stage.
Since blood pressure is variable moment to moment, tracking your own at home involves a cool and collected averaging of multiple blood pressure readings. Sit down, relax for 5 minutes, put the cuff on your left arm about at the level of your heart. Measure it three times in a row. Throw out the first reading, average the second and third readings, record that, sleep on it, repeat the next day. Send us your week-long average, then put the blood pressure monitor in the closet for a couple months before repeating.
Chronic hypertension is associated with a significant increase in heart attacks, strokes, and chronic kidney disease (https://www.nejm.org/doi/full/10.1056/NEJMoa1803180, and https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/486523).
According to the American College of Cardiology/American Heart Association (ACC/AHA), roughly half of people with chronic hypertension do not have adequate blood pressure control (https://tinyurl.com/ydzxyyp6).
In a meta-analysis of over one million adults ages 40-90, risk began to rise in all age groups with blood pressures greater than 115/75 mmHg, and for every 20 mmHg higher systolic and 10 mmHg higher diastolic blood pressure, the risk of death from heart disease or strokes doubled (https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(02)11911-8/fulltext).
In next week’s newsletter we’ll discuss what is known about the benefits of using lifestyle and/or pharmacology to lower your blood pressure.
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