# What is the surface area to volume (SA:V) ratio of a red blood cell?

According to this author, red blood cells (RBCs) are biconcave to allow easier bending. The standard explanation in biology for higher surface area to volume ratios is that it improves reaction rates. When a RBC squeezes through narrow veins I imagine that it gets deformed. Considering that a RBC's function is to exchange oxygen in narrow capillaries, I was wondering whether it is appropriate to reason that the biconcave shape promotes gas exchange. So what is the SA:V of a biconcave RBC and by how much does the SA:V change depending on where in the body the RBC is traveling?

I googled "surface area of a red blood cell" and this paper was the first result. It should answer your first question. Though it was unclear to me what the surface area unit of measure was, which may require a bit further reading. There's also this article, which goes a lot more into the math of calculating these two things.

As for your second question about how much it changes, intuitively I would guess very little and it probably does not significantly change exchange rates. I couldn't find any research on the topic. The hard part is defining all the shapes they may get squeezed into, then either calculating or measuring SA:V. Possible? Surely, a well written computer model could do it at some point. But worth the time/money? Probably not.

• The first article is interesting. SA:V ratio is mentioned a few times but without specific numbers. Table 1 in the article shows RBC volumes and Table 2 shows RBC surface areas. However, there is no approximation of the ratio. Dividing the entries in the tables with each other gives lower than expected results. The SA:V of a sphere, for example, is 4.836 One would expect the SA:V ratio of a RBC to be higher than that. Googling "surface area to volume ratio of a red blood cell" doesn't return the results I'm looking for either. Plenty of references to the SA:V being high, but no approximations. Jan 4 '16 at 11:35
• Can you run me through the calculation you're using to get 4.836? When I run it for a sphere of 6um diameter I get 1,000,000. Jan 4 '16 at 17:09
• See this link. Jan 4 '16 at 17:12
• I see the number, but I'm still unclear on how it's derived. Jan 4 '16 at 17:30
• I don't know either. Jan 4 '16 at 19:07

https://arxiv.org/ftp/arxiv/papers/1403/1403.7660.pdf

human erythrocyte avg dia: 7.2, vol 91.31 cubic microns, surface area 136.55 square microns