Today’s article has been written by our physician contributor.
In this age of technology patients have unparalleled access to their own health information, such as laboratory test results. But what do those results mean?
That’s where your physician comes in. We are experts in helping you interpret information about your health and your body, diagnosing, and helping you manage complications.
What do basic labs include?
When a doctor orders basic labs, this usually includes a complete blood count (CBC) with a differential, electrolytes, urea, and creatinine.
The CBC is a profile of the cells in your blood. The cells in your blood can be broken down into three main types:
- Red blood cells (RBC), which carry oxygen bound to a molecule called hemoglobin (HGB)
- White blood cells (WBC), which make up your immune system and have various roles
- Platelets, which help your blood clot
The “differential” is where the white blood cells are broken down into their subtypes, primarily neutrophils, lymphocytes, eosinophils, basophils, and monocytes.
A CBC includes several other values such as the mean cell volume (MCV), mean cell hemoglobin (MCH), hematocrit (HCT), and red blood cell distribution width (RDW). These are ways of quantifying size, shape and constituents of the red blood cells. Today we will focus on the CBC as well as MCV (the average volume of the red blood cells).
Lab reports often flag a numerical value if it is higher or lower than a normal range based on an average across a population. Sometimes a value might be a little bit high or low with minimal significance; other times, a value might be in the normal range but actually indicate an underlying diagnosis when taken in your clinical context. This is why your physician is an indispensable tool when interpreting these values!
When evaluating your red blood cells, your physician will focus on hemoglobin and MCV. If the hemoglobin is lower than the normal range, this is a condition called anemia. If the value is significantly low, some people notice symptoms such as fatigue, lack of energy, lightheadedness, or shortness of breath. Anemia may have a multitude of possible causes. A few examples are listed below.
- Bleeding in the stool, urine, or anywhere else
- Iron deficiency (generally also associated with a low MCV)
- Vitamin B12 or folate deficiency (generally associated with a high MCV)
- Chronic disease which suppresses the production of blood cells
- Inherited conditions such as sickle cell anemia or thalassemia
- Certain medications such as methotrexate, hydroxyurea, or chemotherapy agents
A high hemoglobin value can be normal if you live at a high altitude. It may be seen in smokers. It can be a clue that you have trouble breathing while asleep, a condition called obstructive sleep apnea. Or, it may indicate an overproduction by the bone marrow, the factory that produces your blood cells.
White blood cells (WBC) make up an important part of our immune system. The WBC may be elevated if you have an infection (such as pneumonia, bladder infection, even the common cold), or chronic inflammation (rheumatoid arthritis, fatty liver disease, among many others). Looking at the differential, your physician may discover a clue about the kind of infection; for example, if the neutrophils are elevated, it is likely a bacterial cause.
The WBC may be low in certain kinds of infections (for example, lymphocytes may be low in viral infections) and in liver disease. Sometimes having abnormal WBC may indicate a problem in the bone marrow and may prompt your physician to order additional tests.
Platelets form an important part of your clotting system which prevents you from bleeding excessively. The platelets may be high in infection, inflammation, or if the bone marrow is inappropriately producing too many platelets. Platelets can be low if they are being used up (e.g. active bleeding), or in patients with enlarged livers or spleens from a variety of causes. Some people develop an autoimmune condition where they inappropriately produce antibodies that target their own platelets for destruction. Sometimes low platelets might indicate a problem in the bone marrow. If your platelet count is less than 50, you may notice easy bruising or bleeding, and your physician may need to investigate further before you have any surgeries to avoid excess bleeding risk.
If your hemoglobin, white blood cells, and platelets are all low, this is a condition called pancytopenia. This generally indicates a problem in the factory (bone marrow), but can also be seen in some stages of liver disease. In this case, your physician may refer you to a hematologist for an expert opinion and further investigation.
What are electrolytes?
Electrolytes are the salts in your blood. They are necessary for chemical reactions, energy production and general function of various cells, including nerve cells and heart cells. The primary electrolytes measured are sodium (Na), potassium (K), and sometimes calcium (Ca), magnesium (Mg), and phosphate (PO4). Each of these may be low in malnutrition.
Sodium may be low in liver, kidney or heart disease. It may be elevated in states of dehydration. Potassium may be low in patients with chronic diarrhea or vomiting. It can be elevated in kidney disease. The other electrolytes (Ca, Mg, PO4) can give clues about a new problem with your diet, your kidneys, or whether a chronic condition is present. Derangement of each of these electrolytes has a specific set of symptoms your physician may ask you about, ranging from muscle weakness to breathing difficulties or heart palpitations.
Urea is derived from the breakdown of protein in your body. It may be elevated if you eat a lot of protein-rich food, but more commonly in kidney disease. A low urea is not of particular importance, although it may be a clue you do not have enough protein in your diet.
Creatinine is a molecule in your blood produced from the turnover of muscle cells. We use it as a marker to tell us about kidney function. It is not perfect particularly in underweight or overweight people, but provides an estimate of kidney function. When the creatinine value is combined with age, the glomerular filtration rate (GFR) can be calculated (a more accurate quantification of kidney function). A high creatinine means your body is not eliminating this molecule at a fast enough pace. A high creatinine and low GFR may indicate dehydration, bleeding, an obstruction of the urinary system, or a primary problem with the kidney itself. Your doctor may choose to do additional tests, such as urine tests or an ultrasound of the kidneys if creatinine is elevated. A low creatinine generally has no clinical significance, and can be seen in patients with low muscle mass.
Knowledge is power. We hope you feel empowered today to be more involved with your care and have gained some confidence in understanding blood basics. Remember, any information you read on the internet, including this post, is not meant to replace a visit with your doctor. That is the only setting where you can be examined and results can be placed in your specific context. Consult with your physician and don’t be afraid to ask about the significance of your results – after all, they are from your body!
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