How to Interpret Your Complete Blood Count (CBC)
The Complete Blood Count is one of the most commonly ordered blood tests. Do you have your results? Let’s learn how to interpret them and when to determine if it’s something more serious.
Jackie is a 36-year-old female accountant who comes to see me for her annual physical. She is generally very healthy. Her employer has enrolled the employees into a work wellness program, in which a discounted health insurance plan rate is provided to those who complete a physical exam once a year. Other than to obtain birth control, it’s the only time of year I see Jackie in the office. 
I run routine blood work as part of her physical and surprisingly find an abnormal result. Jackie was not expecting to the need to return so early after her last visit. My nurse schedules an appointment for her for to discuss her abnormal Complete Blood Count (referred to as a “CBC”). Specifically, her “white blood cell count” (or WBC) component within her CBC was slightly elevated at 13.0 (the abnormal cut-off at this particular lab was 11.5).
What does this mean? Should Jackie be worried? Let’s learn what the CBC is, how to interpret it as a patient, and how to understand when you should be concerned.
What Is a CBC?
A CBC is one of the most commonly run blood tests. Most patients have had at least one at some point in their lives. Doctors may run them during routine physicals or if they are investigating a symptom that warrants a check, such as:
- Fatigue
- Depression
- Increased menstrual bleeding
- Bleeding in the stool, or any orifice (urine, nose, vomit, etc)
- Easy bruising
- Fever of unknown origin
- Recurrent fevers
- Unintended weight loss
- Infections
However, most mildly abnormal results are not concerning and are common. But occasionally, results can reflect something more serious.
Jackie tells me that she has indeed been experiencing some mild fatigue—not enough to keep her from functioning, but enough to serve as a noticeable difference in her daily activities. She also tells me that she’s “always” suffered from mild depression on and off throughout her life, and although she’s been experiencing some relationship difficulties recently, that it’s not necessarily anything out of the ordinary for her.
She denies any skin bruising or abnormal bleeding from any orifice. Except that her periods have been irregular—but again, this is not anything new. She’s had an irregular menstrual cycle since “menarche” (the term doctors use to note the onset of periods).
She also hasn’t experienced any recent illnesses or fevers. Besides inquiring about symptoms of urinary tract infections, pneumonias, upper respiratory tract viruses (the common cold and flu), skin infections, and stomach flu viruses, I also make certain to ask about a common but often ignored source of infection – dental decay. Jackie reassures me that she’s last seen a dentist 6 months ago and that her dental hygiene is up to par.
I also track Jackie’s weight through time in the electronic medical record (EMR) system, since I’ve been taking care of Jackie as a physician for at least seven years now. If anything, she’s actually gained some weight over the holidays. She reports having gained about six pounds since her mom has been visiting her and baking throughout the holiday season.
Interpreting a CBC
A CBC has various components, but the most important values that doctors look for most involve the following:
White Blood Cell Count (WBC):
According to Dr. Edward Ferrer, a primary care doctor and vasectomist in San Diego, he refers to these vital cells as the “Ninja’s” of the immune system. You need them “to ward of infections,” he says. Indeed. These are the cells that your immune system generates when foreign bodies (viruses, bacteria, etc.) are located.
WBCs can be mildly elevated during an infection, but when it’s severely elevated it can be a potential sign of something more serious that requires a more of an urgent care.
We also don’t like it when it’s too low, especially when it’s accompanied by other abnormal values within the CBC as well. However, it is common to see a WBC that chronically and normally sits right below the normal range for some adults, and not necessarily a sign of concern other than to observe through time.
Hemoglobin:
This is one of the most commonly abnormal lab values within the CBC. Primary care doctors (and hematologists) see this one every single day. Is it always concerning? No. But it should not be ignored either.
Infrequently, a low hemoglobin can be a sign of malignancy—the first etiologic thought is colon since microscopic (meaning, naked to the eye) bleeding in the stool can be released stealthily by the colon, and very gradually through time. Another potential malignancy that causes anemia is the blood disorders—any disorder that affects the bone marrow can stop producing red blood cells. These are the cells that carry hemoglobin and oxygen. Examples include myelodysplastic syndrome, leukemias, and lymphomas.
In young child-bearing aged women like Jackie, however, the most common cause of anemia is due to increased vaginal bleeding. Hormonal imbalances, such as Polycystic Ovarian Syndrome, or anatomical challenges with the uterus, such as those with benign fibroid tumors of the uterus, can experience excessive vaginal bleeding. And hence, anemia.
Those who are deficient in Vitamin B12 or Folate, most commonly in those who drink excessive amounts of alcohol, can also experience anemia.
Whatever the cause may be, it’s important to find it and understand why you are anemic.
Platelets:
Platelets are vital to the cessation of the bleeding process. They clump together and stop the bleeding as a team. If there’s not enough of them, the risk of bleeding is high—most especially if there is a traumatic event. When there’s too many, it may be a reflection of excessive production by the bone marrow, rendering the exclusion of blood disorders as a potential cause.
CBC Conclusion
Knowing all of this, it’s important to see Jackie face-to-face in order to not only obtain a thorough history (including symptoms and signs of those with an elevated WBC), but also a thorough physical exam that also assess for the various causes mentioned previously.
Jackie’s exam was normal. After obtaining a second set of labs, I not only repeated the CBC that revealed a relatively unchanged WBC, but also included a pregnancy test, which very surprisingly was positive. Pregnancy is also another cause of a leukocytosis.
Jackie has had abnormal periods her entire life, so she was quite surprised to find that she was pregnant. She did admit to inconsistent use of her birth control since she’s had some relationship mishaps along the way.
Another mystery diagnosis solved.
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Please note that all content here is strictly for informational purposes only. This content does not substitute any medical advice, and does not replace any medical judgment or reasoning by your own personal health provider. Please always seek a licensed physician in your area regarding all health related questions and issues.
Image courtesy of Shutterstock.
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About the Author
Dr. Sanaz Majd is a board-certified Family Medicine physician who graduated from Drexel University College of Medicine in Philadelphia. Her special interests are women’s health and patient education.
