Diagnostic and Laboratory Testing

Diagnostic laboratory testing is used to confirm or rule out particular diseases and disorders. Because modern medicine has become extremely complex, yet is subject to economical restrictions, the interpretation of test results is rarely left to the physician alone. Nurses must also be able to interpret diagnostic test results to help develop effective treatment (Pagana & Pagana, 1999).

This page offers a glossary of some of the major tests. Often the results of a test may be skewed by variations among patients. Some of these variables include:

Age:

Pediatric and geriatric patients may have a range of normalcy that is slightly different from middle-aged patients

Gender:

Values differ between males and females, usually because of the increased muscle mass in males and female hormonal fluctuations.

Race:

While race generally does not affect laboratory test results, it is of more importance regarding certain genetic diseases.

Pregnancy:

The biochemical and hormonal changes of pregnancy can significantly alter test results.

Food ingestion:

Many serum values are affected by what the patient has eaten. Patients are often asked to fast before undergoing diagnostic tests.

A • B • C • D • E • F • G • H • I • J • K • L • M • N • O • P • Q • R • S • T • U • V • W • X • Y • Z

-- A --

ACTH (serum)

ACTH is a blood test used to indicate the causes of hormone imbalances. Secreted by the pituitary gland, ACTH regulates adrenal gland production of cortisol.

Normal range: 9 to 52 pg/ml (picograms per milliliter)

Abnormal ACTH Levels
Greater-than-normal levels	Lower-than-normal levels
Addison's disease related to deficient production by the adrenal gland Cushing's disease related to pituitary tumor ectopic tumor producing ACTH	Cushing syndrome related to adrenal tumor exogenous Cushing's syndrome from prolonged use of steroid hormones pituitary insufficiency

Antinuclear antibodies (ANAs)

The ANA test is used to screen for autoimmune diseases, systemic lupus erythematosis (SLE) in particular.

Common ANAs and Associated Diseases
ANA	Diseases
Anticentromere	CREST syndrome
Anti-ENA	SLE
Antinucleolar	Scleroderma, SLE
Anti-RNP	Scleroderma, SLE
Anti-Smith	SLE

Antiphospolipid antibodies

Found in approximately 40% of patients with SLE (systemic lupus erythematosis), the anti-phospholipid antibodies include anticardiolipin antibodies (ACAs) and lupus anticoagulant. SLE patients with ACAs and lupus anticoagulant are at risk for developing antiphospholipid antibody syndrome: thrombosis, recurrent spontaneous abortion, and thrombocytopenia. They may also develop neuropsychiatric disorders.

ACAs	Normal level
Immunoglobulin G (IgG)	< 23 g/L
Immunoglobulin M (IgM)	< 11 mg/L

Apolipoproteins

A blood test used to evaluate risk of developing atherosclerosis and peripheral vascular disease. Apoplipoproteins are important in lipid transport and facilitating cellular uptake of lipids. Apo A-I is associated with HDL (the "good cholesterol" and Apo B is associated with LDL (the "bad" cholesterol).

Apo Type	Adult Normal Value
Apo A-I	Male: 75-160 mg/dl Female: 80-175
Apo B	Male: 50-125 mg/dl Female: 45-120 mg/dl

Aspartate aminotransferase (AST)

Formerly called serum glutamic-oxaloacetic transaminase (SGOT), this enzyme is concentrated in highly metabolic tissues, such as heart muscle, liver cells, and skeletal muscle cells. Damaged cells release AST, causing serum levels to rise. Serum levels of AST become elevated 8 hours following injury, peak at 24-36 hours, and return to normal levels in 3-7 days. Elevations in AST may be caused by heart attacks (myocardial infarction) or liver damage.

Age	Normal Value (U/L)
0-5 days	35-140
< 3 yrs	15-60
3-6 yrs	15-50
6-12 yrs	10-50
12-18 yrs	10-40
Adult	8-20
Females	Slightly higher than males
Elderly	Slightly higher than adults

-- B --

Blood pressure

Blood Pressure and Age Group
Age Group	Normal	Hypertensive
Infants	80/40	90/60
Children 7-11 yrs	100/60	120/80
Teenagers 12-17 yrs	115/70	130/80
Adults 20-45 yr 45-65 y Over 65 yr	120-125/75-80 135-140/85 150/85	135/90 140/90 - 160/95 160/90 (borderline)

-- C --

Cardiac enzymes

Used to determine the time of a recent MI, the cardiac enzyme series comprises AST (aspartate transaminase), CPK (creatinine phosphokinase), and LDH (lactate dehydrogenase).

Timing of Appearance and Clearance of Cardiac Enzymes
	Hours		Days
Enzyme	Rises	Peaks	Returns to normal
Total CPK	4-6	18	2-3
AST	8	12-48	4
LDH	24	72	8-9
Troponin T	4-6	10	2-3
Troponin I	4-6	4	2-3

Calcium

Calcium is required for muscle contractility, cardiac function, neural transmission, and blood clotting.

Normal Blood Calcium Levels
Adults	8.7-10.6 mg/dl
Children	8.8-10.8 mg/dl
Infants (10 days-2 yrs)	9.0-10.6 mg/dl
Newborns (<10 days)	7.6-10.4 mg/dl

Potential Critical Values
< 8.5 mg/dl	Hypocalcemia	Increased neuromuscular excitability (Trousseau and Chvostek signs) Skeletal muscle cramps Tetany, larygospasms, asphyxia, death
> 10.5 mg/dl	Hypercalcemia	Decreased neuromuscular excitability (weakness, CNS depression, stupor, coma) EKG may show shortened QT May have increased risk of fractures

Carbon dioxide (CO₂)

Carbon dioxide levels indicate serum levels of bicarbonate ions (HCO₃^-). Both are important in regulating acid-base balance.

Normal Values of Carbon Dioxide
Adults	23-30 mEq/L
Children	20-28 mEq/L
Infants	20-28 mEq/L
Newborns	13-22 mEq/L

Cholesterol

This blood test is used to screen patients for risk of developing atherosclerosis. In addition to total cholesterol, lipoproteins and triglycerides are also measured. Elevated cholesterol levels are associated with higher risk of heart disease, and lower than normal levels are associated with liver disease and malnutrition.

Age (yrs)	Normal Value	Low Risk	Moderate Risk	High Risk
2-19	120-200	< 170	175-185	> 185
20-29	< 200	< 200	201-220	> 220
30-39	< 200	< 220	221-240	> 240
>40	< 200	< 240	241-260	> 260

Chvostek sign

An indicator of hypocalcemia, a postive Chvostek sign is seen when a facial spasm occurs after tapping the facial nerve about 2 cm. in front of the ear.

Cortisol (24-hour urine)

Cortisol levels are tested to confirm hypercortisolism, then further tests are done to determine the cause.

• Normal Levels: 10 to 100 mcg/24 h. (micrograms per 24-hours)

Abnormal Cortisol Levels
Increased levels	Decreased levels
ACTH-secreting tumor Cushing's syndrome pituitary tumor	Addison's disease hypopituitarism congenital adrenal hyperplasia

Creatinine (24-hour urine)

Normal values : 0.8 to 1.4 mg/dl.

• Urine creatinine levels are used to evaluate kidney function and muscle metabobolism.
• Creatinine is a breakdown product of creatine, which is an important constituent of muscle. Daily production of creatinine depends on muscle mass, which fluctuates very little in normal conditions. However, when muscle is being used as an energy source, creatinine levels are altered.

CT scan (Computerized tomography or CAT scan)

CT scans (or possibly an MRI or Ultrasound) are used to detect tumors in the brain or the rest of the body. For examples, see X-ray tests for adrenal gland tumors.

-- D --

Dexamethasone suppression test

This test is performed when adrenal disease is suspected; it can differentiate adrenal disease (altered response to ACTH) from pituitary disorders (altered production of ACTH). Dexamethasone mimics the action of cortisol and, through negative feedback, it suppresses ACTH production in normal people. If a patient is given Dexamethasone and the pituitary gland responds by reducing production of ACTH, then we can surmise that (1) the pituitary gland is functioning and (2) the problem lies with the adrenal glands' response to ACTH.

-- E --

Electrocardiogram (EKG, ECG)

An electrodiagnostic test, the EKG measures heart rate and rhythm. The normal heart rate is 60-100 beats/minute.

Electrolytes

See specific serum electrolytes: calcium, potassium, or sodium.

-- G --

Glucose (Blood)

Normal range: 64 to 128 mg/dl (milligrams per deciliter)

Abnormal Glucose Levels
Hyperglycemia	Hypoglycemia
acromegaly Cushing's syndrome diabetes mellitus hyperthyroidism pancreatic cancer pancreatitis pheochromocytoma (very rare) insufficient amount of insulin excessive food intake	hypopituitarism hypothyroidism insulinoma (very rare) injection of too much insulin insufficient dietary intake

-- H --

Heart Rate

(see pulse rate)

-- L --

Lipoproteins

The lipoproteins high density lipoproteins (HDL), low density lipoproteins (LDL), and very low density lipoproteins (VLDL) transport cholesterol, triglycerides, and other fats through the blood stream. HDL is thought to carry cholesterol out of the body by transporting it to the liver for excretion. Cholesterol carried by LDL is deposited in body tissues and associated with peripheral vascular disease.

Cholesterol-HDL Ratio as an Indicator Coronary Artery Disease Risk
	Ratio
Risk	Male	Female
Half average	3.4	3.3
Average	5.0	4.4
2 x average	10.0	7.0
3 x average	24.0	11.0

-- P --

Potassium (K)

The major cation inside the cells, potassium is important in maintaining neuromuscular excitability. Potassium levels are regulated by

1. Aldosterone - increases loss through urination
2. Sodium reabsorption - as sodium is conserved, potassium is lost.
3. Acid-base balance - alkaline states tend to lower serum potassium levels. Acidic conditions tend to raise serum potassium levels.

Normal Potassium Levels
Adults	3.5-5.5 mEq/L
Children	3.4-4.7 mEq/L
Infants	4.1-5.3 mEq/L
Newborns	3.9-5.9 mEq/L

Potential Critical Values
< 2.5 mEq/L	Hypokalemia	Decreased muscle contraction (weakness, paralysis, hyporeflexia, ileus) Cardiac arrhythmias (flattened T wave, prominant U wave)
> 6.5 mEq/L (adults) > 8.0 mEq/L (newborns)	Hyperkalemia	Irritability, nausea, vomiting, intestinal colic, diarrhea EKG: peaked T-wave, wide QRS complex, depressed ST segment

Pulse Rate

The pulse is the rate at which your heart is beating. As the heart forces blood through your body, you can feel a throbbing in the arteries wherever they come close to the skin surface. The pulse can be taken at the wrist, neck, or upper arm.

• Count the pulse after the person has been sitting or resting quietly for 5 to 10 minutes.
• Place two fingers gently against the wrist as shown (don't use your thumb).
• If it is hard to feel the pulse in the wrist, locate the carotid artery in the neck, just to either side of the windpipe. Press gently.
• Count the beats for 30 seconds, then double the result for beats per minute.

Normal Resting Heart Rate (beats/min.)
Infant - 1 year	100-160
1 - 6 years	65 - 140
7 - 10 years	60 - 110
11 - 20 yrs	50 - 100
20-40	70-75
50	70
60	65
70	62
80	59

Sources:

• Healthwise Handbook
• Bullock, B.L.(1996)

-- R --

Respiration Rate

The respiration rate is how many breaths are taken in one minute.

Normal Resting Respiration
Infant - 1 year	40 - 60 breaths/minute
1 - 6 years	18 - 26 breaths/minute
7 - adult	12 - 24 breaths/minute

Source: Healthwise Handbook

-- S --

SGOT

Serum glutamic-oxaloacetic transaminase. See AST.

Sodium (Na)

Serum sodium is balanced by dietary intake and renal excretion. Sodium levels are regulated by aldosterone (conserves sodium) and natriuretic hormone that encouarges sodium excretion.

Normal Sodium Values
Adults	135-145 mEq/L
Children	135-145 mEq/L
Infants	134-150 mEq/L
Newborn	134-144 mEq/L

Potential Critical Values
< 120 mEq/L	Hyponatremia	Weakness, confusion, lethargy, stupor, coma
> 160 mEq/L	Hypernatremia	Dry mucous membranes, thrist, agitation, restlessness, hyperreflexia, mania, convulsions

-- T --

Triglycerides

Measured by a blood test, triglyceride profiles are used to assess the risk of developing coronary and peripheral vascular disease. Triglycerides are produced by the liver and carried in the blood stream by lipoproteins LDL and VLDL. Excess triglycerides are deposited in fatty tissues (including the blood vessels!) as stored energy.

Normal Values (mg/dl)
Age	Male	Female
Adult	40-160	35-135
16-19 yrs	40-163	40-128
12-15 yrs	36-138	41-138
6-11 yrs	31-108	35-114
0-5 yrs	30-89	32-99

Trousseau's sign

Characteristic of hypocalcemia, Trousseau's sign is a carpopedal spasm that occurs when the blood supply is reduced to the arm for 3 minutes. Typically happens when a blood pressure cuff is applied.

-- U --

Urinalysis

Urinalysis (UA) comprises multiple tests on a urine specimen. The urine appearance, color, and odor are observed. A dipstick test measures pH and the presence of proteins, glucose, ketones, blood, and hemoglobin. Microscopic examination reveals the presence of RBC's, WBC's, casts, crystals, and bacteria.

Normal Values (mg/dl)
Characteristic	Value	Indications
Appearance	Clear	Pathological: pus, RBCs, or bacteria can cloud urine. Physiological: Ingesting certain foods (large amounts of fat, ureates, or phospates
Color	Amber yellow	Concentration. Dilute urine is straw colored and concentrated urine is deep amber
Odor	Aromatic	Normal: slight ammonia. Diabetic ketoacidosis: Acetone (strong, sweet odor) UTI: may have a foul odor
pH	4.6 - 8.0	Acidic acidosis starvation dehydration Diet high in meat products or cranberres Alkaline Alkalosis UTI Diet high in citrus fruits or vegetables
Specific gravity	1.005-1.030	Low specific gravity may be caused by renal disease, overhydration High specific gravity indicates dehydration
Proteins	0-8 mg/dl 50-80 mg/24 hrs at rest < 250 mg/24 hrs after strenuous exercise	Glomerulonephritis (damaged glomerular membrane) due to pregnancy (preeclampsia), diabetes mellitis, amyloidosis, multiple melanoma.
Ketones	Negative	A breakdown product of fat metabolism, excess ketone production is assoiciated with uncontrolled diabetes, starvation/fasting, high protein diets, and alcholism.
Glucose	Negative	Physiological causes: ingestion of high-carbohydrate meal Pathological: Diabetes mellitus
RBCs	< 2 per slide	Increases may indicate renal trauma, damage to renal tubules, or bladder irritation
WBC's	0-4 per low power field	Increased WBC's may indicate a UTI
Urobilinogen	0-4 mg/24 hrs	Liver damage, tumor, or gallstones
Crystals	Negative	Kidney stones, parathyroid abnormalities, malabsorption
Casts	Negative	Proteinuria and stasis within renal tubules.
Bacteria	Negative culture	UTI