# Help with renal plasma flow, derivation?

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#### axeon123

##### New Member
15+ Year Member
FA 2009 p437 for reference

RBF = RPF / (1 - Hct)

This is the equation they give for renal blood flow. Can someone explain how the equation works? RPF = amount of plasma that passes through the kidney, and RBF I am guessing is the amount of whole blood passing through. Why did they divide by (1 - Hct) term? It'll make it easier to understand what is going on. Thanks.

#### lord_jeebus

##### 和魂洋才
Moderator Emeritus
20+ Year Member
HCt is the percentage of blood that is not plasma, so (1 - HCt) is the percentage of blood that is plasma.

#### axeon123

##### New Member
15+ Year Member
HCt is the percentage of blood that is not plasma, so (1 - HCt) is the percentage of blood that is plasma.

Ooo okay, so then to make it simpler

RBF * (1 - Hct) is the same as multiplying the blood by the fraction that is *not* blood, ie plasma, so you get RPF. Now I don't have to memorize the equation then because it makes more sense this way. #### lord_jeebus

##### 和魂洋才
Moderator Emeritus
20+ Year Member
Ooo okay, so then to make it simpler

RBF * (1 - Hct) is the same as multiplying the blood by the fraction that is *not* blood, ie plasma, so you get RPF. Now I don't have to memorize the equation then because it makes more sense this way. I would not remember it as "the fraction that is not blood" because plasma is part of blood. Rather, (1 - Hct) = "the fraction that is not cells" = "the fraction that is plasma."

I'm sure you understood it that way, but this might avoid some confusion among someone who encounters this thread in the future.