Measured and calculated erythrogram values

To follow up on what we covered in class today, this is how erythrogram values are determined using an automated hematology analyzer: 

RBCs (x 10⁶/µL) – the analyzer counts the # of RBCs in a given volume of blood, and also determines the size (volume – see MCV) of each RBC. 

Hgb (g/dL) – the analyzer lyses RBCs and measures [Hgb] by spectrophotometry. 

MCV (fL) – the analyzer software calculates an average value based the sizes of all RBCs measured. 

Hct (%) – the analyzer software calculates a value based on RBCs and MCV.  Working through the math on a hypothetical blood sample with an RBC concentration of 6.5 x 10⁶/µL and an MCV of 72 fL:

     RBC               = 6.5 x 10⁶/µL = 6.5 x 10¹²/L  

     MCV               = 72 fL = 72 x 10^-15 L

     Hct                  = RBC x MCV

                             = (6.5 x 10¹²/L) x (72 x 10^-15 L)

                             = 468 x 10^-3 = 0.468 = 46.8%

If you just used the reported values for RBC and MCV without converting the volumes to liters (instead of µL or fL), then it would work out like this: 

     Hct                  = RBC x MCV
                             = 6.5 x 72 = 468 (decimal points are off w/out unit conversions) 

MCH (pg) – the analyzer software calculates a value based on Hgb and RBCs.  Working through the math on a hypothetical blood sample with a Hgb concentration of 15.4 g/dL and an RBC concentration of 6.5 x 10⁶/µL: 

     Hgb                 = 15.4 g/dL = 15.4 g/10^-1 L

     RBC               = 6.5 x 10⁶/µL = 6.5 x 10¹²/L

     MCH               = Hgb ÷ RBCs
                             = 15.4 g/10^-1 L ÷ 6.5 x 10¹²/L
                             = 2.37 g x 10^-11 g = 23.7 g x 10^-12 g = 23.7 pg 

If you just used the reported values for Hgb and RBC without converting the volumes to liters (instead of dL or µL), then it would work out like this: 

     MCH               = Hgb ÷ RBCs
                            = 15.4 ÷ 6.5 = 2.37 (decimal points are off w/out unit conversions)

MCHC (g/dL) – the analyzer software calculates a value based on MCH and MCV.  Working through the math on a hypothetical blood sample with a MCH of 23.7 g/dL and an MCV of 72 fL:

     MCH               = 23.7 pg = 23.7 g x 10^-12 g

     MCV               = 72 fL = 72 x 10^-15 L

     MCHC            = MCH ÷ MCV
                             = 23.7 g x 10^-12 g ÷ 72 x 10^-15 L
                             = 0.329 g/10^-3 L = 32.9 g/10^-1 L = 32.9 g/dL 

If you just used the reported values for Hgb and RBC without converting the picograms to grams and the femtoliters to liters, then it would work out like this: 

     MCHC            = MCH ÷ MCV
                             = 23.7 ÷ 72 = 0.329 (decimal points are off w/out unit conversions) 

RDW (%) – the analyzer software calculates a value (SD/mean) based the sizes of all RBCs measured.