Articles, The Olive: September

Biometric Numbers: False Positives


goldfish with shark fin is example of a false positiveBiometric screenings provide numbers that are important for understanding your health status. But unfortunately sometimes the objective data can give what are known as a “false positive”. This means that your data may show that you have medium or even a high risk level for a chronic disease like obesity, cholesterol, or hypertension. But even though the data are correct, the interpretation is not.

Below are three examples of biometric screening data that can give you false positives, leading you to believe that you may have a chronic condition when you may not at all. As with all medical topics, always consult your doctor for any questions or clarifications that you need.


The Body Mass Index (BMI)

The BMI is a measure of overweight and obesity. However, this biometric has a serious flaw because it basically compares your height to your weight, gets a ratio of one to the other, and uses that determine whether you are of normal weight, overweight, or obese.

On the face of it, it seems completely commonsensical. For example, if two people are both exactly the same height at six foot tall, but the first one weighs 200 pounds while the other person weighs 180 pounds. Clearly, the first one should be more overweight.

But the problem with the logic is that our muscle weighs more than our fat. So people who lift weights or even those who have more muscle tone will read higher on the BMI scale. Athletes who are obviously fit and healthy can have a BMI reading that puts them into the overweight or obese category.

This is a clear false positive.



Many things can impact your cholesterol levels and produce a temporary change in your body’s chemistry. If you get your screenings down during a swing in your cholesterol, the number read may not reflect the actual value. Here are some ways that could happen:

Short term reductions in lipid levels:

  1. If you have had a recent cardiac event like a heart attack or stroke.
  2. If you have had recent surgeries or infections.

Short term increases in lipid levels: 

  1. Corticosteroids and estrogen hormones can temporarily raise your lipid levels. If you have been prescribed these medications, let your doctor know.
  2. Pregnancy can increase cholesterol levels. In fact, tests for cholesterol are not considered reliable until 3 months after the baby is born.

Short term changes:

  1. Eating before you get your blood drawn can create these alterations in cholesterol. The safest way to take your cholesterol reading is to fast for 12 hours beforehand so there is no food on board to muddy the waters.
  2. Along this line, drinking alcoholic beverages also can change the cholesterol readings.


Blood Pressure

Your blood vessels have tiny muscles around them like little sleeves. And when these mini-muscular sleeves contract, it can pinch down the bore of the blood vessel. When the vessel squeezes in on the blood, suddenly the space inside gets much smaller, even though the amount of blood stays the same!

When that happens, the blood presses harder on the walls of the vessels and this causes your blood pressure reading to increase. When the vessels relax again, the pressure comes back down as well.

In addition to constriction of the blood vessels, many things cause temporary changes in blood pressure: when you wake up in the morning, go from sitting to standing, walk a flight of stairs, and even when you are nervous. All these variables can cause false positives as well, as when the reading is correct but the interpretation is not.

Consult your doctor of course, but also understand that you can have the most confidence in your blood pressure reading if you take it multiple times in the same way each time. Be calm, not winded, and sitting down. Also, having those multiple readings taken to confirm your values can provide more certainty in your actual blood pressure.


Will Clower

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