Red top tubes, also known as red top vacutainer tubes, are commonly used in healthcare settings to collect blood samples for a variety of medical tests. The red top refers to the color of the rubber stopper on the tube, which allows laboratory technicians to easily identify the tube type. But what exactly does a red top tube test for? Here is an in-depth look at what these tubes are used for.
Contents of a Red Top Tube
Red top tubes contain no additives or anticoagulants. This allows the blood to clot naturally after it is drawn. The main contents of a red top tube include:
- Whole blood
- Clot activator – a silicone coating on the interior wall of the tube speeds up clotting
The lack of additives makes the red top tube ideal for tests that require serum, the liquid portion of blood that remains after clotting. Serum contains antibodies, proteins, enzymes, sugars, fats, minerals, hormones, and metabolites.
Biochemical Tests
Many routine biochemistry tests require serum from a red top tube. These include tests for:
- Lipid profile – measures cholesterol, triglycerides, LDL, and HDL
- Blood glucose
- Blood urea nitrogen (BUN) – kidney function test
- Creatinine – kidney function test
- Electrolytes like sodium, potassium, chloride
- Liver enzymes like ALT, AST, ALP
- Total protein
- Albumin
- Bilirubin – evaluates liver function
Red top tubes allow these biochemical analyses to be performed on a patient’s serum sample. The lack of additives ensures there is no interference with the results.
Blood Cultures
Blood cultures are commonly drawn when there is suspicion of bacteremia or sepsis. They require inoculation of blood into special culture bottles that allow microbial growth. Red top tubes provide whole blood needed for blood cultures to check for:
- Bacterial infections like Staphylococcus, Streptococcus
- Fungal infections like Candida
Early detection from blood cultures drawn into red top tubes allows targeted antibiotic treatment for dangerous bloodstream infections.
Hormone Levels
Many hormones are measured from serum derived from red top tubes. This includes tests for:
- Thyroid hormones T3, T4, TSH
- Sex hormones like testosterone, estrogen, FSH, LH
- Cortisol
- hCG to detect pregnancy
- Insulin
- Vitamin D
As hormones can be very sensitive, avoiding any additives ensures accuracy when measuring serum hormone levels.
Therapeutic Drug Monitoring
Levels of certain medications can be measured using serum from a red top tube. This therapeutic drug monitoring helps assess proper dosing and toxicity. Examples include:
- Phenobarbital
- Phenytoin
- Carbamazepine
- Valproic acid
- Digoxin
- Lithium
- Gentamicin
- Vancomycin
Red top tubes allow serum drug levels to be analyzed accurately without interference from additives.
Serology Testing
Serology is the study of blood serum. Red top tubes provide serum needed to evaluate the immune response through antibodies. Serology tests drawn from red tops include:
- Blood typing
- Antinuclear antibody (ANA) for autoimmune diseases
- Rheumatoid factor for rheumatoid arthritis
- C-reactive protein (CRP) to assess inflammation/infection
- Cyclic citrullinated peptide (CCP) antibody for rheumatoid arthritis
These immunologic markers are best measured in plain serum without additives.
Blood Banking Tests
Red top tubes provide the serum needed for fundamental blood banking tests prior to transfusion including:
- ABO typing
- Rh typing
- Antibody screening
- Cross matching
These tests require intact reactivity of serum antibodies and compatibility factors to ensure safe blood transfusions.
Specialized Testing
In addition to routine testing, red top tubes allow specialized analyses including:
- Troponin levels to detect heart injury
- Creatine kinase (CK) to assess muscle damage
- Procalcitonin to evaluate severe bacterial infections
- BNP to measure congestive heart failure severity
Red top tubes give labs the flexibility to perform and add on these unique tests as needed for particular patients.
Considerations for Red Top Tubes
While red top tubes have many uses, there are a few special considerations when drawing and handling them:
- Invert tube multiple times after collection to properly mix with clot activator
- Store upright to maintain tube integrity
- Transport to lab within 2 hours as clot can begin to retract after 1 hour
- Centrifuge sample within 2 hours to obtain optimal serum separation
- Hemolysis can occur with rough handling
- Limited stability for potassium due to cell leakage from clot
Overall, proper collection technique helps maintain sample integrity for the myriad of tests performed from red top blood collection tubes.
The Takeaway
Red top tubes have a wide array of applications in the clinical lab due to their additive-free nature. They provide serum needed for general health screening tests, blood cultures, hormone levels, therapeutic drug monitoring, serology, blood banking, and specialized testing. While handling considerations exist, the versatility of the red top tube makes it a laboratory staple and essential for quality patient care.
| Test | Use |
|---|---|
| Lipid profile | Measures cholesterol, triglycerides, LDL, HDL |
| Blood glucose | Screens for diabetes |
| BUN/Creatinine | Assesses kidney function |
| Electrolytes | Measures sodium, potassium, chloride |
| Liver enzymes | Evaluates liver function |
| Total protein | Screens nutrition status |
| Blood cultures | Detects bloodstream infections |
| Hormone levels | Monitors endocrine status |
| Therapeutic drug monitoring | Assesses medication levels |
| Serology | Measures immunologic markers |
| Blood bank testing | Determines blood type and compatibility |
This table summarizes some of the many tests that can be performed using a red top tube specimen.
