How Many Red Blood Cells Do We Lose A Day?

Quote of the Day

Well, did we pass?

— Paul Samuelson's PhD adviser to the rest of Paul's dissertation committee after his thesis defense. Samuelson, arguably the greatest economist of his generation, was intimidating to his professors even as a student.


Introduction

Figure 1: Image of Human Red Blood Cells.

Figure 1: Image of Human Red Blood Cells (Source).

I regularly visit the RefDesk website to pick up general information. Refdesk has a section that contains a Fact of the Day from the Random History website. Unfortunately, these "facts" are occasionally just plain wrong (example). Today, another one of these random facts did not seem correct and I thought I would perform a quick Fermi analysis here to show that it cannot be correct. I assume that they confused hours and minutes in their analysis. I will present my argument below.

The questionable random "Fact of the Day" is a simple one.

Every hour, about 180 million newly formed red blood cells enter the bloodstream. Red blood cells are basically shells. Before being released from the bone marrow, most of a red blood cell's internal structure is ejected, creating a disc-shaped balloon that is ideal for carrying oxygen and a small amount of the body's carbon dioxide.

A rough mental calculation told me that this number was way too small. I will perform a more detailed calculation below that supports my argument that this number is low by a factor of ~60. Did they really mean to say one minute instead of one hour? That is my theory.

Analysis

Figure 2 shows my detailed calculations with links that support each result.

Figure 2: My Calculations for the Average Number of Blood Cells Lost Per Minute.

Figure 2: My Calculations for the Average Number of Blood Cells Lost Per Minute.

Number of Red Blood Cells in a Cubic mm Average Lifespan of a Red Blood cell Blood Volume in a Human Male Total Number of Red Blood Cells in a Human Male Red Blood Cells Lost Per Second

Conclusion

My calculations show that ~180 million red blood cells are replaced every minute – not ~180 million every hour as stated in the "Fact of the Day."

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2 Responses to How Many Red Blood Cells Do We Lose A Day?

  1. timhughes@ieee.org says:

    People with artificial heart valves loose even more cells. The early caged ball valves (The ones that made an annoying loud click) were particularly bad for causing haemolysis.

    The design of heart valves is fascinating. The natural valves are an amazingly efficient design.

    Tim Hughes

     
  2. Barbara Kalbus says:

    You are correct. 2 million per second!

     

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