A little story about the journey of body fluids in the clinical laboratory.
Learn about laboratory medicine and clinical chemistry. The complete blood count (CBC) measures the general properties of blood cells to help doctors predict changes in health status.
Imagine the bright lights of a large clinical laboratory where various mechanical beasts lurk. Looming arms pick up samples from fields of racks. The test tubes contain all sorts of body fluids. A long metal arm reaches out to scan samples. The robotic line delivers tubes to the slender silver lanes where specific instruments await.
The instrument scans the sample again before engulfing the tube inside the darkened panels. Deep inside the instrument, magic happens. A sharp pipet needle pierces the top of the tube. A few drops of body fluid are removed.
The pipet arm delivers the drops to a tiny testing vessel. Inside the instrument, specific health marker testing occurs. The results will help guide doctors in healthcare decisions.
Body Fluid Types in the Clinical Laboratory
Clinical laboratories test every fluid inside your body: urine, blood, saliva, cerebrospinal fluid, and genetic material like DNA (Figure 1).
Clinical Lab Testing Groups
Scientists group body fluids to analyze and report test results (Table 1). The categories help laboratory organization.
| CATEGORY | TEST TYPES | |
| CLINICAL CHEMISTRY | Urinalysis, Hematology, Hemostasis | |
| IMMUNOLOGY | Infectious Disease, Toxicology, Drug Monitoring, Point of Care, Cancer, Thyroid, Bone, Kidney, Maternal Screening, Cardiac, Diabetes, Growth Panel, Allergy | |
| MICRO-ORGANISM | Microbiology, Mycology, Parasitology, Pathology, Virology | |
| MOLECULAR | Genetic Analysis, Micro-organism Identification, Viral Testing |
Within clinical testing categories, additional specializations exist. For example, molecular testing can include:
- Maternal screening
- Paternity testing
- Cancer mutation analysis
Clinical Chemistry Testing
Laboratory medicine can be difficult to explain. This article focuses on complete blood count (CBC), a type of clinical chemistry testing. By measuring the general properties of blood (hematological characteristics), doctors screen for illnesses.
Hematology and the Study of Blood
Hematology studies blood components. Viscous red blood carries nutrients, oxygen, and salts to tissues and organs. Blood transports the body’s immune cells and proteins to prevent infection. Blood also takes waste products to organs for excretion. This warm dark fluid sustains life, making up 7 to 8% of total body weight (2).
About 55% of blood exists as plasma, the rest contains cellular material (1):
- Red blood cells (RBCs)
- White blood cells (WBCs)
- Platelets
The blood vessel contains RBCs, WBCs, and platelets swimming in plasma (Figure 2). Plasma consists of 90% water (1, 2). The remaining 10% consists of albumin, fibrinogen, and globulin (1, 2). These proteins help maintain immunity and homeostasis. Homeostasis means keeping elements balanced. Homeostasis balances temperature shifts, acid levels, and blood pressure inside blood vessels.
What is a Red Blood Cell (RBC)?
When total blood volume in the body amounts to 1 ½ gallons (6 Liters), giving a few tablespoons (about 30 mL) to help determine the cause of illness doesn’t seem like much. Clinical chemistry instruments test a few blood drops. The CBC measures the volume, size, number, and types of blood cells.
Imagine being immersed in the bloodstream. Slowly puttering along the passageways an RBC passes. The large red RBC looks like a slightly inflated balloon with the center caving inward (Figure 3).
RBCs act like rafts, traveling about ½ miles per hour. Red blood cells carry oxygen to the body. Red blood cell flexibility makes squeezing through small vessels (capillaries) easy. An RBC lasts about 110 days before recycling and replacement takes place (3).
Diseases can affect the movement of RBCs through the small blood vessels. Illnesses impact the shape and stretch of the RBC (3). Commonly ordered, the complete blood count (CBC) looks at elements of RBCs. Blood analyzers today provide precise measurements of a single RBC (3).
Looking at Complete Blood Count (CBC) Testing
The CBC checks RBCs, WBCs, and platelets in the blood. The test determines the amounts of hematocrit (RBC percentage) and hemoglobin (the oxygen-carrier in RBCs). These help assess the ability to use oxygen. The platelet count is reported. The test counts the number, volume, and size of RBCs and WBCs. The cell differential sorts the WBCs and RBCs (Figure 4).
Gauging the variation between RBCs means comparing size and shape:
- Mean corpuscular volume (MCV)
- Mean corpuscular Hemoglobin (MCH)
- Mean corpuscular Hemoglobin concentration (MCHC)
- Red cell distribution width (RDW)
Is CBC Testing Useful?
Yes, CBC measurements aid doctors in diagnosing a wide range of illnesses:
- Anemia
- Infection
- Cancer
Out-of-range CBC results alert doctors to changes in health (3). Doctors will seek out causes of illness (3). The CBC provides clues to help identify types of anemia: hemolysis (hemolytic anemias) versus deficiency (iron deficiency, pernicious anemia, etc.) (2).
Out-of-range CBC may point to another illness like an infection or anemia (2). These health conditions can alter the shape or quantity of RBCs and WBCs (2). Doctors don’t diagnose a disease based on CBC values alone.
Doctors interpret CBC with clinical history, symptoms, and other test results (2). Discuss any concerns or questions with a healthcare professional for a thorough explanation. And remember, questions lead to better health!
References & Links
References:
1. AlMomani, T.D.; Vigmostad, S.C.; Chivukula V.K.; Al-zube, L.; Smadi, O.; BaniHani, S. Red; Blood Cell Flow in the Cardiovascular System: A Fluid Dynamics Perspective; Critical Reviews in Biomedical Engineering; 40(5): 427-440 (2012)
2. Linne’, Jean J; Ringsrud, Karen M; Basic Techniques in Clinical Laboratory Science, 3rd Edition, Mosby Year Book Inc.; (1992)
3. Higgins, John M; Red Blood Cell Population Dynamics; Clin Lab Med; March; 35(1): 43-57 (2015)
Links to More Lab Testing Information
To learn more about these types of tests, see the links below:
https://medlineplus.gov/lab-tests/
https://www.mayocliniclabs.com/test-catalog
https://www.mountsinai.org/health-library
