1/8 This always confused me as a trainee, so I figured it would be worth reviewing! What parameter should you interpret to determine if a patient is generating an appropriate amount of RBCs?
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2/8 While you need all this information, the answer is Reticulocyte Index (RI)! This is an underutilized test and should be one of the first tests you use when working up anemia. So how do we calculate this and what are those other terms? Let's review.
3/8 An Absolute Reticulocyte Count (ARC) is often calculated by your lab, but you need to be sure you are looking at the right parameter. Lots of folks use MDCalc to calculate RI, but the calculator gives you an ARC and RI.
Look at the first parameter to enter - it's a %!
4/8 That means if your lab only gives you an ARC and does not give you a % of reticulocytes, you shouldn't use MDCalc. Ready for some math?
5/8 We first need to calculate a Corrected Reticulocyte Count (CRC) using the following equation. If you use the equation below, make sure you to convert the % (i.e. an ARC of 2% should be input as 0.02).
6/8 We're almost there! To calculate an RI, you have to take the CRC and divide it by the Maturation Correction.
7/8 What the heck is a Maturation Correction?
Prematurely released reticulocytes will have a LONGER lifespan than your average reticulocyte, so we have to adjust for that.
8/8 And now you can finally interpret your RI! To summarize:
🩸Calculate an RI as a first step in assessment of anemia
🩸Check if your lab calculates an ARC for you
🩸Pay VERY close attention when using percentages for your calculations
🩸Don't forget about the maturation factor!
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