Lab Diagnostics: Blood

GM unit 7

Learning Targets

• Identify common blood tests and their purpose in diagnostics.

• Discuss lab skills, safety, and procedure.

Blood as a Diagnostic Tool

• Blood is often used as a diagnostic for several reasons: – Blood is easily accessible. It is relatively harmless

to obtain and low risk. It is also not expensive to test blood.

– Blood can give us lots of information. It contains cells and plasma, and gives a good general status of the body function.

Limitations of Blood Tests

• Cannot be treated as absolutes in most cases, due to margin of error. – When we test blood we take only a small sample,

which should be representative, but is not always. – Lurking variables can skew results. – Issues in the central nervous system are hard to

see with blood tests due to blood brain barrier.

Lab Safety Basics

• Remember Standard Precautions– Just because the patient is not standing their, you

should still observe all appropriate precautions with body fluids.

• Be especially careful with transferring blood and obtaining specimens. – Higher risk for contamination.

• Sharps are common. – Lots of needles are used and disposed in the lab setting.

Do it correctly.

Lab Skills• Venipuncture – obtaining blood via a peripheral stick.

– This is adequate for most lab requests. – Involves locating, accessing, and then de-accessing a vessel

near the peripheral surfaces of the skin. • Arterial Puncture – obtaining blood from an artery.

– This is higher risk due to pressurized blood in these vessels. – After care is especially important. Lack of appropriate care can

lead to bleeding or hematoma. • Obtaining Blood from a Central Line

– This is a special skill, usually only performed by an RN. – Proper technique and precautions use to high risk of infection.

What are those colored tubes about?

• They are called “Vacutainers”– Test tubes used in the tests are voided of air, and therefor will

pull a specimen in, only until the appropriate amount is present. • The color to indicates what type of additive is in the tube.

– Some tubes have enzymes that prevent clotting, cause separation of blood parts, etc.

– This is needed depending on the different test to be run. • Draw order:

– It does matter what order tubes are drawn in. – Some tests need to be drain first, others should have blood

wasted (or used in other tests) before hand.

Blood Components

• When we test blood, we have several factors to look at: – Plasma, which contains lots of solutes (hormones,

nutrient levels, sugar, waste products, electrolytes, chemical factors etc.)

– Red Blood Cells (which we can count, test for reaction properties, shape, etc.)

– Platelets (tell us about blood clotting)– White blood cells (there are many types, and different

levels of each can indicate disease or infection)

Hematocrit

Manual Blood Counts

A Closer Look at Blood Components

Red Blood Cells• We can look at the

shape/size of the cells, the number of cells or even specific chemical factors about the cells to give us information about the body.

• The normal range for RBC is: 4.2 to 6.1 million per microliter.

Hemoglobin• This usually corresponds to

RBC, but is specifically is the oxygen carrying molecules in the cell.

• Normal range: 12-18 grams per deciliter.

• In both of these, men tend to run higher than women.

A Closer Look at Blood Components

Albumin• Albumin is the prime

protein in blood, and creates the appropriate level of osmotic pressure to prevent loss of excess blood into the tissues.

• Low levels can indicate liver disease or starvation.

Platelets• Platelets are a key part of

the clotting cascade. They are cell fragments made from special bone marrow cells.

• These cells must work together with the various clotting factors to stop bleeding when it occurs.

White Blood Cells

Elevated Total WBCs• This is a count of all white

blood cells (5 types). Further more specific counts may be used to figure out specific problems.

• Increased levels indicate stress, or infection. Decreased levels indicate immune suppression.

Elevated Individual Types of WBCs

• Certain types of WBCs respond to different needs in the body. – Elevated Eosinophils may

indicate a parasite infection or allergic reaction.

– Immature white blood cells indicate a serious systemic infection called sepsis.

– Decreased levels of Killer T Cells indicates advancing HIV

Common Blood Tests: The Blood Count (CBC)

• A complete blood count (CBC) is a blood test used to evaluate your overall health and detect a wide range of disorders, including anemia, infection and leukemia.

• A complete blood count test measures several components and features of your blood, including:– Red blood cells, which carry oxygen– White blood cells, which fight infection– Hemoglobin, the oxygen-carrying protein in red blood cells– Hematocrit, the proportion of red blood cells to the fluid component, or plasma,

in your blood– Platelets, which help with blood clotting

• Abnormal increases or decreases in cell counts as revealed in a complete blood count may indicate that you have an underlying medical condition that calls for further evaluation.

Common Blood Tests: BMP and CMP

CMP – gives basic blood chem, plus information about liver and kidney function. • Albumin – blood protein• Alkaline Phosphatase – liver test• ALT - liver test• AST - liver test• BUN – kidney function indicator• Creatinine – kidney function test• Calcium• Chloride• Carbon Dioxide• Glucose• Potassium• Sodium• Serum Bilirubin• Total Protein

BMP – gives a basic picture of blood chem, plus kidney function.

• BUN – Blood Urea Nitrogen• Creatinine• CO2• Glucose• Chloride• Potassium • Sodium

Common Blood Tests: ANA and ESR

ESR – Erythrocyte Sedimentation Rate

• Literally measures o how fast the RBCs sink to the bottom of the tube.

• Faster Rates occur in diseases that result in systemic inflammation (autoimmunity issues especially)

ANA – Antinuclear Antibody• This test measures the

presence of antibodies in the blood that are targeted at the body’s own tissues.

• These rates are elevated in autoimmune issues, liver disease and inflammatory issues.

Common Blood Tests: Coomb’s Test

• This test measures antibodies that are in the blood (indirect) or are bound to the red blood cells (direct). – Elevated levels may occur in reactions to

transfusion, infectious disease, autoimmune disease.

Common Blood Tests: Liver Function Tests

• Measures of several blood components can give indication to liver function: – ALP – AST/ALT– Bilirubin

• These markers and enzymes indicate either directly or indirectly damage to the liver.

• Liver disease may also result in elevated inflammation markers, low blood counts or blood protein.

Common Blood Tests: Kidney Function

• Tests that monitor the function of the kidneys mainly rely on measuring levels of waste product in the blood. As levels rise, it indicated the kidneys are not working. – BUN– Creatinine

• Other indicators of kidney issues can be found in urine, or be expressed as electrolyte imbalance or anemia.

Common Blood Tests: Blood Culture

• If a septic infection is suspected (an infection which is spreading in the blood), blood cultures can be performed. – Just like cultures of wounds or other fluids, blood

is obtained and allowed to “grow out” on a medium.

– Then, any growth is tested as to what it is and what medication is effective.

Common Blood Tests: Blood Clotting Studies

• Other than the number of platelets present, several other measures can be made concerning how long it takes the blood to clot. This can be used to identify a problem or to see if medication meant to slow clotting is effective. – INR: international normalized ratio is a measure of how

long it takes certain factors to begin working in the clotting cascade. It is used to monitor medication levels.

– PT/PTT – measures how long it takes for Prothrombin and thrombin to activate in the clotting cascade.