RBC shape abnormalities

There was a good question in class today about abnormal erythrocyte shape.  The catch-all term for RBC shape abnormalities is poikilocytosis.  I mentioned that the types of "poik" that you should know for the purpose of the course are spherocytes (which usually indicate extravascular hemolysis), schistocytes (RBC fragments, also called schizocytes, which are often seen in patients with DIC or other types of "microangiopathies"), and eccentrocytes (which, like Heinz bodies, are a manifestation of oxidative damage to RBCs).  Your textbook has a nice section on poikilocytosis, summarized in Table 3.7, and some good images in Plates 5 and 6.  The poikilocytosis section of Cornell's e-ClinPath website is also a good resource.

Hope y'all have a great Labor Day weekend.  See you on Tuesday.

1st v. 2nd edition of required textbook

I had a good question about the required text:  "Does it matter if we buy the 1st or 2nd edition of the required textbook?  The second edition is obviously much more expensive, and I was wondering if you knew of any significant differences in the newer edition?"

This was my response:  The differences in the content of the 1st and 2nd editions are relatively small, but not irrelevant.  I think the library has copies of both, so I suggest you take a look at them yourself before you decide.  Remember, you have free access to the e-book of the 2nd ed.

Plasma protein terminology: "globulins" v. "immunoglobulins"

As Dr. Flatland indicated, the value for globulin concentration on a serum or plasma chemistry panel is determined mathematically:

[Total protein] - [Albumin] = [Globulins]

So, in the context of clinical chemistry, "globulins" means any proteins detected by the biuret method, except albumin.

Sometimes people say "globulins" when they really mean "immunoglobulins", which means antibodies.  An immunoglobulin (Ig) is a type of globulin, but the terms are not synonymous because the globulin fraction also comprises many non-Ig proteins, including coagulation factors, acute phase proteins, transport proteins, enzymes, hormones, cytokines ... and I'm probably leaving some out.

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.

About this blog

This blog is an optional resource for VM888 (Clinical Pathology) in 2014, not an official part of the course. It’s a forum to address issues that arise in lectures and labs, answer questions and exchange ideas, share thoughts about how the class is going, and provide links to other websites relevant to veterinary clinical pathology. I encourage you to be an active participant and post questions or comments. 

All VM888 students and course instructors will soon receive an invitation by e-mail to become members of this blog. If you'd like to be able to post to the blog, please accept the invitation. Only members will be allowed to make postings. If you're not interested in being an active blog participant you can still follow the discourse by visiting this website.

See you soon.