How Much Blood is "One Tiny Drop"?
Photo of One Drop, the First of About Six

How Much Blood is "One Tiny Drop"?

Do you know how much blood is really in one tiny drop? Ever since the rise and fall of Theranos, the public has been enthralled (and skeptical) with the notion that a full routine panel of blood tests could be performed with just “one tiny drop” of blood of capillary blood. We see drops of liquid all the time, so we have an intuitive sense of the size of a drop, and many people who test their blood glucose at home have experience seeing drops of blood on their fingertips. But in quantitative terms, how big is a drop of blood?

Relatively few sources actually attempt to quantify the size of a drop. Scientists often measure small liquid volumes in microliters, abbreviated μL (or uL when you don’t want to use special symbols). A microliter is one-thousandth the volume of a milliliter. A milliliter is one cubic centimeter, whereas a microliter is one cubic millimeter.

I’ve seen articles estimate the size of a drop of blood as 25uL, 35uL, and 50uL. That’s a pretty broad range…so what’s the truth? We ran the experiment, and the answer (as usual) is that it depends. When dispensing blood using a pipette with a narrow aperture, we measured 25uL, and when dispensing blood using a pipette with a wide aperture, we measured 40uL. When we squeezed blood straight from the finger we measured 34uL, but with a pretty wide variance in size (standard deviation 4uL). Drops can be very different in size depending on who and where they come from, which you may think about the next time you look at a wet sink or windshield.

So when people ask if a full routine panel of blood tests can be run with just a drop of blood, we round to 35uL to answer the question. We collect two different kinds of samples for BetterWay. Our serum samples are collected using a gold tube with a minimum fill volume of 435uL, which rounds to 12 drops. Our whole blood samples are collected using a lavender tube with a minimum fill volume of 225uL, which rounds to 6 drops. To run a full panel of blood tests, we need one serum sample and one whole blood sample, which you could estimate at about 18 drops.

So what’s the answer to “can you run a full panel of blood tests with just a drop of blood?” The answer is no. But with BetterWay, we are working to create a reality where our customers can think in terms of drops of blood instead of having to think about giving vials of blood.

It's great to see such enthusiasm for making blood testing more understandable! Your determination to share knowledge is inspiring and can truly make a difference in the field. Looking forward to seeing the articles you share. What specific topics are you planning to cover first?

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Insightful! Thanks, Eric Olson!

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Hugh Chisholm ( Retired )

Director, North American Automation/Implementation.

9 个月

Love this. Hope all Is well. Enjoy following you and your team’s continued successes.

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Hari Nair

PhD/D(ABCC)/MBA I Co-Founder Rhythm Medical I CEO Nyla Laboratories (Acquired) I Advising startup clinical laboratories I Building socially and financially meaningful products, services and companies.

9 个月

Eric Olson great topic. As “a drop” is a subjective quantity (depends on many variables such as the thickness of the orifice, exerted pressure etc), this is a useful approach. Perhaps another way to think about this problem might be to use the standardized dried blood spot circle area (used in routine new born screening) as a defining metric, for example, number of drops (or volume) needed to fill a spot.

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