LECTURE 7: PREANALYTICAL CONSIDERATIONS

preanalytical

phase of the testing process begins for the laboratory when a test is ordered and ends when testing begins.

reference range or reference interval.

vary somewhat from person to person, the results used for comparison become a range of values with high and low limits, commonly called a

Basal state

refers to the resting metabolic state of the body early in the morning after fasting for approximately

12 hours.

Basal state refers to the resting metabolic state of the body early in the morning after fasting for approximately

of diet,

exercise, and other controllable factors

A basal-state specimen is ideal for establishing reference

ranges on inpatients because the effects

age, gender, and conditions of the body

Basal state is influenced by a number of physiologic patient variables such as

higher in newborns than in adults.

red blood cell (RBC) and white blood cell (WBC) values are normally

creatinine clearance, a measure of kidney function,

is directly related to the age of the patient, which must be factored in when test results are being calculated.

Decreased oxygen levels at higher altitudes

cause the body to produce more RBCs to meet the body’s oxygen requirements; the higher the altitude, the greater the increase.

hemoglobin (Hgb) and hematocrit (Hct)

have higher reference ranges at higher elevations.

C-reactive protein and uric acid

increase at higher elevations as well

Urinary creatinine and plasma renin

analytes that decrease in value at increased altitude

Dehydration

(decrease in total body fluid)

persistent vomiting or diarrhea, and causes hemoconcentration

Example of Dehydration

RBCs, enzymes, iron (Fe), calcium (Ca), sodium (Na), and coagulation factors.

Blood components affected by dehydration include

ingestion of food and drink.

Blood analyte composition can be altered by the

8 to 12 hours

Patients are typically asked to fast approximately

Fasting

is normally done overnight after the last evening meal, with specimens collected the following morning before the patient has eaten.

NPO

Patients are allowed to drink water during fasting unless they are

Ammonia, urea, and uric acid levels

may be elevated in patients on high-protein diets.

Cortisol and ACTH levels

have been shown to increase with the consumption of beverages containing caffeine.

Glucose (blood sugar) levels

increase dramatically with the ingestion of carbohydrates or sugar-laden substances

2 hours

Sugar laden substance can return ti normal within

Eating carbohydrates

can also increase insulin levels.

Hgb levels

can decrease and electrolyte balance can be altered by drinking excessive amounts of water and other fluids.

Lipid levels

increase with ingestion of foods such as butter or margarine, cheese, cream, and some enteral (tube feeding) preparations.

lipemia.

Abnormally increased blood lipid content is

called

lipemic

Lipids do not dissolve in water and thus high levels of lipids are visible in serum or plasma, causing it to appear milky (cloudy white) or turbid, and the specimen is described as being

Lipemia

can be present for up to 12 hours, which is why accurate testing of triglycerides (a type of lipid) requires a 12-hour fast.

similar substances in meat and certain vegetables

test methods that detect occult (hidden) blood in stool specimens

Triglycerides, certain liver enzymes, and other liver function analytes

are increased by chronic

consumption or recent ingestion of large amounts of

alcohol, which can also cause hypoglycemia.

Malnutrition and starvation

also affect the

composition of blood analytes.

Long-term starvation

decreases cholesterol, triglycerides, and urea levels and increases creatinine, ketone, and uric acid level

diurnal

(happening daily)

circadian

(having a 24-hour cycle)

activity, eating, daylight and darkness, and being awake or asleep.

Factors that play a role in diurnal variations include

melatonin levels are affected by light

increase at night,

daylight hours.

when it is dark, o decrease during

Maximum renin and thyroid-stimulating hormone (TSH) levels

normally occur in the predawn hours of the morning during sleep,

Peak cortisol levels

Normally occur later in the morning, around 8:00 A.M.

aldosterone, bilirubin, cortisol, hemoglobin, insulin, iron, potassium, testosterone, and RBCs.

exhibit diurnal variation with highest levels occurring in the morning include

normally lowest in the morning.

Blood levels of eosinophils, creatinine, glucose, growth hormone (GH), triglycerides, and phosphate are

timed tests

Tests influenced by diurnal variation are often ordered as

Chemotherapy drugs

can cause a decrease in blood cells, especially WBCs and platelets.

Many drugs are toxic to the liver

as evidenced by increased levels of liver enzymes such as aspartate aminotransaminase (AST)—also called serum glutamic-oxaloacetic transaminase (SGOT), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH) and decreased production of clotting factors.

Opiates

such as morphine increase levels of liver and pancreatic enzymes.

Oral contraceptives

can affect the results of many tests.

Steroids and diuretics

can cause pancreatitis and an increase in amylase and lipase values.

Thiazide diuretics

can elevate calcium and glucose levels and decrease sodium and potassium levels.

azotemia

Other thiazide-type medications that lower

blood volume can increase blood levels of

nitrogenous waste such as urea, a condition called

“compounds reacting unfortunately as the desired.”

An acronym for substances that interfere in the testing process is CRUD, which stands for

4 to 24 hours

according to CAP guidelines, drugs that interfere with blood tests should be stopped or avoided

48 to 72 hours

Drugs that interfere with urine tests should be avoided for

Exercise

affects a number of blood components, raising levels of some and lowering levels of others

Arterial pH and PaCO2 levels

are reduced by exercise.

Glucose, creatinine, insulin, lactic acid, and total protein

can be elevated by moderate muscular activity.

Potassium (K+)

is released from the cells during exercise, increasing levels in the plasma. Levels generally return to normal after several minutes of rest.

Skeletal muscle enzyme levels

are increased by exercise, with levels of creatine kinase (CK) and lactate dehydrogenase (LDH) remaining elevated for 24 hours or more.

Vigorous exercise shortly before blood

collection

can temporarily increase cholesterol levels by 6% or more.

hemostasis.

Vigorous or sustained exercise can also affect

Fever-induced hypoglycemia

increases insulin levels, followed by a rise in glucagon levels and also increases cortisol and may disrupt its normal diurnal variation.

RBC, Hgb, and Hct normal values

are higher for males than for females.

patient’s gender

affects the concentration of a number of blood components.

Jaundice, also called icterus

is a condition characterized by increased bilirubin (a product of the breakdown of RBCs) in the blood, leading to deposits of yellow bile pigment in the skin, mucous membranes, and sclerae (whites of the eyes), giving the patient a yellow appearance

icteric

means relating to or marked by jaundice and is used to describe serum, plasma, or urine specimens that have an abnormal deep yellow to yellow brown color due to high bilirubin levels

Jaundice

in a patient may indicate liver inflammation caused by hepatitis B or C virus.

10%

standing position causes blood fluids to filter into the tissues, decreasing plasma volume in an adult up to

30 minutes of standing

a significant increase in potassium (K􏰌) levels occurs within

30 minutes

Plasma aldosterone and renin change more slowly but can double within an hour. ▪ Consequently, patients are required to

15 minute

The RBC count o

Pregnancy

causes physiologic changes in many body

systems. Consequently results of a number of laboratory

tests must be compared with reference ranges

established for pregnant populations.

increased cholesterol, cortisol, glucose, growth hormone, and triglyceride levels and WBC

Patients who smoke prior to specimen collection may have

Chronic smoking

often leads to decreased pulmonary function and increased RBC counts and hemoglobin levels.

Stress

is also known to decrease serum iron levels and increase adrenocorticotropic hormone

Other hormones

that can be affected include aldosterone and TSH, and GH in children.

hemoconcentration

Extensive sweating without fluid replacement, on the other hand, can cause

burned, scarred, or tattooed areas

Veins are difficult to palpate or penetrate in these areas.

does

not contain dye.

if you have no choice but to draw in an area with a tattoo, try to insert the needle in a spot that

Edema

a is swelling caused by the abnormal accumulation

of fluid in the tissues.

hematoma

is a swelling or mass of blood (often clotted) that can be caused by blood leaking from a blood vessel during or following venipuncture.

lymphostasis

Lymph node removal, which is typically part of the

procedure, causes

lymphedema

Impaired lymph flow makes the arm susceptible to swelling, called

Obese (extremely overweight)

patients often present a challenge to the phlebotomist. Veins on obese patients may be deep and difficult to find.

long length of new Penrose drain tubing or a long Velcro closure strap

often works better than a latex or vinyl strap. A blood pressure cuff can also be used.

arterial line

is a catheter that is placed in an artery. • It is most commonly placed in a radial artery and is typically used to provide accurate and continuous measurement of a patient’s blood pressure. • It may also be used to collect blood gas and other blood specimens and for the administration of drugs such as dopamine.

arterial or central venous catheter

A needleless closed blood sampling device is sometimes connected to an

heparin or saline lock

is a catheter or cannula connected to a stopcock or a cap with a diaphragm (thin rubber-like cover) that provides access for administering medication or drawing blood.

48 hours.

It is often placed in a vein in the lower arm above the wrist and can be left in place for up to

saline lock

is sometimes flushed with heparin also. Heparin readily adheres to surfaces; therefore it is difficult to remove all traces of it.

Intravenous

IV) means “of, pertaining to, or within a vein.”

central vascular access device (CVAD)

consists of tubing inserted into a main vein or artery.

Central venous catheter (CVC) or central venous line

a line inserted into a large vein such as the subclavian and advanced into the superior vena cava, proximal to the right atrium. The exit end is surgically tunneled under the skin to a site several inches away in the chest. One or more short lengths of capped tubing protrude from the exit site which is normally covered with a transparent dressing.

Implanted port

a small chamber attached to an indwelling line that is surgically implanted under the skin and most commonly located in the upper chest or arm. The device is located by palpating the skin and accessed by inserting a special needle through the skin into the self-sealing septum (wall) of the chamber. The site is not normally covered with a bandage when not in use.

Peripherally inserted central catheter (PICC)

→ a line inserted into the peripheral venous system (veins of the extremities) and threaded into the central venous system (main veins leading to the heart). It does not require surgical insertion and is typically placed in an antecubital vein just above or below the antecubital fossa.

Coban.

One solution is to place a clean, folded gauze square over

the site and wrap it with self-adherent bandaging material

such as

15 minutes

Care must be taken not to wrap it too tightly, and the patient should be instructed to remove it in

5 minutes

If the patient is alert, mentally competent, and willing,

another alternative is to instruct him or her to hold

pressure for

special armbands or have allergy-specific warning signs

Patients with known allergies often wear

appropriate personnel should be notified.

Pressure must be maintained over the site until the bleeding stops. If the bleeding continues after 5 minutes,