Part 1: The CBC

Knowledge is power. I think most people would agree with this statement. We collect knowledge over the course of our careers, in order to gain power. Maybe it is the power to recognize the changes in patterns or at least recognize that something is “off” or doesn’t make sense. Maybe it is the power to more fully understand our patient’s situation or the situation a crew finds themselves in. Hopefully, it is the power to act – to make wiser, more accurate, more “therapeutic”or “helpful” decisions.

“With great power comes great responsibility (attributed to Voltaire, but more famously: Uncle Ben). So, if we attain information, don’t we have the responsibility to act on that information? What if we only have half of the information? Holy cow, get to the point woman! What are you trying to say?

As flight crew members we are in a unique role. We have more required education and a higher scope of practice than our comrades on the ground. We are put in positions where we get to essentially function like physicians without the depth of education, credentials and … let’s face it… insurance. We are taught a lot of “stuff” … but do we always necessarily know how to apply it? How does it all translate?

This was a long, drawn-out introduction to the subject of serum lab values. Frankly, not a lot of disciplines seem to have in-depth education on how to interpret serum lab values. Sure, we learn the basics – High WBC count = bad. High or low serum potassium = bad. High lactate = bad. A lot of times we are charting these values, but do we really understand what they mean? If we did, would it change how we take care of patients? I believe the answer is yes.

I think lab values intimidate many Critical Care Transport Providers. It’s partially because we just don’t get enough education and practice working with these values. We never develop a level of comfort required to incorporate lab interpretation into our transports.  So… in other words, everyone should have a basic understanding of serum lab values, but how much you want to use them to direct your care is up to you. I like the power that this knowledge brings – power to provide the very best patient care within my ability and scope. Hopefully, I can live up to that.

Let’s begin. The format of this series of articles is going to be strange, in order to keep the content straightforward. Stay with me. The objectives?

  • Learn normal and abnormal for common labs
  • Identify patients at-risk for lab abnormalities
  • Correlate abnormal lab values to disease processes
  • Use lab values to create a patient-specific plan of care

The rules?

  1. As we rule one diagnosis in, we are looking to rule other diagnoses out at the same time.
  2. Learn what the rules are, before you learn when to break them.
  3. Remember that the body doesn’t always read the book: Just because we say that it should behave a certain way, or because it does most of the time… it doesn’t’ mean that it always will.
  4. When you see a value followed by “-ish,” it just means that there are different resources that give different ranges.

First thing’s first … Let’s look at The Complete Blood Count (CBC.)

White Blood Cell Count (WBC’s):

Normal: 4000-10,000-ish

Most people are familiar with the WBC count and we all look to see if the WBC count is up or down. A decrease in the WBC count indicates that neutrophil consumption surpasses supply or immunosuppression has occurred. An increase in the WBC count can indicate infection, but it also may just indicate insult. What counts as an insult? Anything that can cause inflammation for sure: surgery, asthma, myocardial infarction, burns, allergic reactions, smoking (Riley & Rupert,2015). There can be metabolic causes for increasing WBC’s, such as Diabetic Ketoacidosis (DKA) or pre-eclampsia… maybe your patient experienced some type of poisoning? Did you know the act of hemorrhaging alone can cause an elevation in WBC’s? Leukemias can… no brainer. Anything that causes extreme physical stress can cause the WBC count to increase, such as strenuous exercise or pregnant moms experiencing labor. Moral of the story? Elevated WBC count does not necessarily equal infection!

Remember that infections need a source. If you see an elevated WBC count and want to diagnose your patient as infected, there needs to be at least a “suspected”source.  If a source can’t be identified, then maybe it’s not an infection.

If bands are present, they are shown in the differential of the CBC. Bands are baby WBC’s (neutrophils). If bands show up, it means that the adults are dying off and the kids are going to war (never good). Segs are the mature guys. If you have a high number of bands present, you have bandemia, which indicates a “left shift” has occurred. (There is a graph that the lab looks at and bands are represented on the left – more bands present? Left shift). The band count is not always available on a CBC, but bands are neutrophils – so if the percentage of neutrophils on your CBC is high, you may indirectly come to the conclusion that your patient has a left shift and has been fighting an infection for at least a couple of days.

Hemoglobin/Hematocrit (H/H)

Normal: Pregnancy: 28-40%, NormalWomen: 37-48%, Men: 45-52%,

We always want to be aware of what the H/H is, because obviously, it’s important to know how many red blood cells are banging around in there. But when we are determining whether our H/H is high or low, we want to look at what’s called the “Rule of the 3”s. Basically: The Hematocrit (HCT) should be roughly 3 times that of the Hemoglobin (Hgb) and the Hgb should be roughly three times that of the Red Blood Cell (RBC) count. Example:HCT=27, Hgb=9 and the RBC’s=3. 27/3=9/3=3. Make sense? (Keep in mind that this rules only applies if your RBC Indices are normal.)

The Hematocrit is what we call a dilutional value. Overhydrated? Hematocrit may break the rule of threes and result low – Dehydrated? The Hematocrit may break the rule of threes and result high (Pagana &Pagana, 1999) – the other value that can be dilutional is the Blood Urea Nitrogen(BUN) on your chem panel. We aren’t going to talk about it a lot, but you can look to see if it is moving in the same way as your hematocrit, in order to corroborate your theory.

One potential way to use this information in transport is a patient with renal failure. We may expect the BUN to be high in a renal failure patient (failing kidneys can’t filter urea) so we can’t count on its accuracy in determining dilution. However, if the hematocrit is high and the patient has signs and symptoms of dehydration or fluid loss, along with a supporting history…this may direct you to a “pre-renal” cause of failure. This patient needs fluid and we can do that!


Basic anemias are fun because you will figure things out and stump other people. Anemias can get detailed, but let’s keep it simple: I like to look at the Mean Corpuscular Volume (MCV). You will find the MCV in the RBC Indices.  The MCV basically describes the size of RBC’s. If the patient’s MCV is low, we call that “microcytic.” Many times, this represents an iron deficiency anemia. Is the MCV high? We call this “macrocytic (Doig& Zhang, 2017).” Macrocyticanemias are many times caused by alcohol abuse or a B12/folate deficiency. Are you wondering if your patient is a drinker? This might give you a clue. Is the MCV normal or “normocytic” and the patient is anemic? This represents acute blood loss or an RBC production problem.


Normal: 0.5 – 1.5%

Reticulocytesaren’t actually part of the CBC, but they apply to our discussion. Reticulocytes are baby RBC’s. If the reticulocyte count is high, this means that the RBC supply is not meeting the demand and the “retics” get kicked out of the nest. This happens because of an ongoing anemia or is a product of the body’s attempt to compensate at high altitude. A low retic count indicates that there is a production problem (Doig & Zhang). Ever heard of Epoetin? So… if we bring this all back together: Normocyticanemia and low retic count? Production problem! Normocytic anemia and high retic count? Blood loss!


Normal: 150,000-400,000-ish

I’m sure someone cares if the platelet count is high, but for us? We care if the platelet count is low (thrombocytopenia). Why? Because without platelets, patients bleed! The low end of normal is 150,000, but we don’t really transfuse patients until they are down to less than 50,000 with signs of bleeding (Kaufman, et al., 2015). There isn’t a lot of magic that a flight crew is going to perform here, However, it helps to understand what’s going on, because it gives us a better picture of our patient. We want to know why the platelets are low. Are they on heparin and their platelets have been trending down? Think HIT (Heparin-Induced Thrombocytopenia!) When the heparin is removed, eventually the platelets go back up. Some disease processes where we would expect to find low platelets include: Disseminated Intravascular Coagulation (DIC) and Thrombocytopenia Purpura (TTP). Still no smoking gun? Let’s look at how the liver is functioning. Liver disease, especially End Stage Liver Disease (ESLD), causes thrombocytopenia. Still no reason for your patient to have low platelets. Could they have cancer? 

Holy crap Johnson! This was probably enough information about the CBC that you are glad to have it, but you don’t want to know any more, am I right? Stay tuned for Part Two: The Metabolic Panel and Liver stuff – even more fun than anemias!


Doig, K.& Zhang, B. (2017). A methodical approach to interpreting the red bloodcell parameters of the complete blood count. Clinical Laboratory Science, 30(3), 173.1

Ishimine,N.,Honda, T., Yoshizawa, A., Kawasaki, K., Sugano, M., Kobayashi, Y., et al.Combination of White Blood Cell count and left shift level real-timely reflectsa course of bacterial infection. (2013). Journal of Clinical Laboratory Analysis, 27:407-411.3

Kaufman, R.M, Djulbegovic, B., Gernsheimer, T., Kleinman, S; Tinmouth, A.T.,  K.E., et al. (2015). Platelet Transfusion: Aclinical practice guideline from the AABB. TheAnnals of Internal Medicine, 162:205-213.

Nader,N.D. (2015). Neutrophilia. Retrieved on January 28, 2017 from

Pagana, K.D. & Pagana, T.J. (1999). Hematocrit. Mosby’s Diagnostic and Laboratory TestReference, 4th Ed. Pgs. 463-464. Elsevier.

Riley, L.K. & Rupert, J. (2015). Evaluation of patientswith leukocytosis. American Family Physician, 92(11), p. 1004-1011.

Schnell, Z.B., Van Leeuwen, A.M. & Kranpitz, T.R.(2003). Davis’s Comprehensive Handbook of Laboratory and Diagnostic Tests withNursing Implications. 2nd Edition. Philadelphia:F.A. Davis Co.Toggle panel: Monarch Sharing Stats


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