Mosby’s Diagnostic & Laboratory Test Reference 12th edition Pagana eBook

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  • Published: 2015
  • ISBN-10: 0323225764
  • ISBN-13: 978-0323225762

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Mosby’s Diagnostic and Laboratory Test Reference 12th edition eBook

Alphabetical Diagnostic and Laboratory Test Reference – A – Pages 1 – 10 (Small Sample)

abdominal ultrasound… 1

abdominal ultrasound (Abdominal sonogram) A

Type of test Ultrasound

Normal findings╇ Normal abdominal aorta, liver, gallbladder,

bile ducts, pancreas, kidneys, ureters, and bladder

Test explanation and related physiology

Through the use of reflected sound waves, ultrasonography

provides accurate visualization of the abdominal aorta, liver,

gallbladder, pancreas, bile ducts, kidneys, ureters, and bladder.

The technique of ultrasonography requires the emission of high-Â.

frequency sound waves from a transducer to penetrate the particular

organ being studied. The sound waves are bounced back to

the transducer and are then electronically converted into a pictorial

image (Figure€1). Real-time ultrasound provides an accurate

picture of the organ being studied. Doppler ultrasound provides

information concerning blood flow to those organs.

The kidney is ultrasonographically evaluated to diagnose

and locate renal cysts, to differentiate renal cysts from solid

renal tumors, to demonstrate renal and pelvic calculi, to document

hydronephrosis, to guide a percutaneously inserted needle

for cyst aspiration or biopsy, and to place a nephrostomy tube.

Ultrasound of the urologic tract is also used to detect malformed

or ectopic kidneys and perinephric abscesses. Renal transplantation

surveillance is possible with ultrasound. One advantage of

a kidney sonogram over intravenous pyelography (see p. 778)

is that it can be performed on patients with impaired renal function

because no intravenous contrast is required.

Endourethral urologic ultrasound can also be performed

through a stent that has a transducer at its end. The stent probe

is placed into the urethra to examine that segment for diverticula.

The stent probe can then be advanced into the bladder where the

depth of a tumor into the bladder wall can be measured. With

the╯use of wire lead guidance, the stent probe can be passed into

the ureter where stones (especially those embedded into the submucosa),

tumors, or extraurethral compression can be identified

and localized. Finally, as the probe is advanced in the proximal

ureter, renal tumors or cysts can be better delineated.

The prostate and the testes are discussed on pp. 754 and 816.

Another use of sonography is in the assessment of the

abdominal aorta for aneurysmal dilation. Sonographic evidence

of an aortic aneurysm greater than 5â•›cm or any size

aneurysm that is documented to be significantly enlarging is an

2â•… abdominal ultrasound

Â.indication for abdominal aorta aneurysm resection. Ultrasound

is also an ideal way to evaluate aneurysm patients before and

after surgery.

Ultrasound is used to detect cystic structures of the liver

(e.g., benign cysts, hepatic abscesses, and dilated hepatic ducts)

and solid intrahepatic tumors (primary and metastatic). Hepatic

ultrasound also can be performed intraoperatively by using a sterile

probe. This technique allows for accurate location of small,

nonpalpable hepatic tumors or abscesses. The gallbladder and

bile ducts can be visualized and examined for evidence of gallstones,

polyps, or dilation secondary to obstructive strictures or

tumors. The pancreas is examined for evidence of tumors, pseudocysts,

acute inflammation, chronic inflammation, or pancreatic

abscesses. Ultrasound of the pancreas is frequently performed

serially to document and demonstrate resolution of acute pancreatic

inflammatory processes.

FIGURE€1╇ Ultrasound of the abdomen.

abdominal ultrasoundâ•… 3

Because this study requires no contrast material and has no A

associated radiation, it is especially useful in patients who are

allergic to contrast and in those who are pregnant. Fasting may

be preferred, but it is not mandatory. (See discussion of pelvic

ultrasonography [p. 697] for sonographic evaluation of pelvic

organs.)

Interfering factors

• Air impedes transmission of ultrasonic waves into the body.

The use of a lubricant is essential to ensure good transmission

of sound waves to and from the body.

• Barium blocks transmission of ultrasonic waves. For this reason,

ultrasonography of the abdomen should be performed

before any barium contrast studies.

• Large amounts of gas in the bowel distort visualization of

abdominal organs because bowel gas reflects sound. Likewise,

ultrasonic evaluation of the lungs yields poor results.

• Obesity may affect the results of the study because sound

waves are altered by fatty tissue.

• Movement causes artifacts. Some patients may need to be

sedated to remain still. Uncooperative patients (especially

children) may not be candidates for ultrasonography.

• Because ultrasonography requires direct contact of the transducer

and the skin, it may not be possible to perform this

study in postoperative patients with dressings.

• The quality of the ultrasound image and the sufficiency of the

study depend to a very large part on the abilities of the ultrasound

technologist performing the study.

Procedure and patient care

Before

Explain the procedure to the patient.

Tell the patient that fasting may or may not be required,

depending on the organ to be examined. No fasting is

required for ultrasonography of the abdominal aorta, kidney,

liver, spleen, or pancreas. Fasting, however, is preferred for

ultrasound of the gallbladder and bile ducts.

During

• Note the following procedural steps:

1. The patient is placed on the ultrasonography table in the

prone or supine position, depending on the organ to be

studied.

4â•… abdominal ultrasound

2. A greasy conductive paste (coupling agent) is applied to

the patient’s skin. This paste is used to enhance sound

wave transmission and reception.

3. A transducer is placed over the skin.

4. Pictures are taken of the reflections from the organs.

• The test is completed in approximately 20 minutes, usually by

an ultrasound technologist, and is interpreted by a radiologist.

Tell the patient that this procedure causes no discomfort.

After

• Remove the coupling agent from the patient’s skin.

• Note that if a biopsy is done, refer to biopsy of the specific

organ (e.g., liver or kidney biopsy).

Abnormal findings

Kidney

Renal cysts

Renal tumor

Renal calculi

Hydronephrosis

Ureteral obstruction

Perirenal abscess

Glomerulonephritis

Pyelonephritis

Perirenal hematoma

Gallbladder

Polyps

Tumor

Gallstone

Liver

Tumor

Abscess

Intrahepatic dilated bile ducts

Pancreas

Tumor

Cysts

Pseudocysts

Abscess

Inflammation

Bile ducts

Gallstone

Dilation

Stricture

Tumor

Abdominal aorta

Aneurysm

Abdominal cavity

Ascites

Abscess

notes

acetylcholine receptor antibody panelâ•… 5

acetylcholine receptor antibody panel╇ (AChR Ab, A

Anti–AChR antibody)

Type of test╇ Blood

Normal findings

ACh receptor (muscle) binding antibodies: ≤0.02â•›nmol/L

ACh receptor (muscle) modulating antibodies: 0 to 20% (reported

as % loss of AChR)

Striational (striated muscle) antibodies: <1:60

Test explanation and related physiology

These antibodies may cause blocks in neuromuscular transmission

by interfering with the binding of acetylcholine (ACh)

to ACh receptor (AChR) sites on the muscle membrane, thereby

preventing muscle contraction. It is this phenomenon that characterizes

myasthenia gravis (MG). Antibodies to AChR occur

in more than 85% of patients with acquired MG. Lower levels

are seen in patients with ocular MG only. The presence of these

antibodies is virtually diagnostic of MG, but a negative test does

not exclude the disease. The measured titers do not correspond

well with the severity of MG in different patients. In an individual

patient, however, antibody levels are particularly useful in

monitoring response to therapy. As the patient improves, antibody

titers decrease. In adults with MG, there is at least a 20%

occurrence of thymoma or other neoplasm. Neoplasms are an

endogenous source of the antigens driving production of AChR

autoantibodies.

There are several AChR antibodies that can be associated with

MG. The AChR-binding antibody can activate complement and

lead to loss of AChR. The AChR-modulating antibody causes

receptor endocytosis, resulting in loss of AChR expression,

which correlates most closely with clinical severity of disease. It is

the most sensitive test. A positive modulating antibody test may

indicate subclinical MG, contraindicating the use of curare-like

drugs during surgery. The AChR-blocking antibody may impair

binding of acetylcholine to the receptor, leading to poor muscle

contraction. It is the least sensitive test (positive in only 61% of

patients with MG). Not all of the antibodies impair neuromuscular

transmission. For example, striational antibodies are directed

at sarcomeric proteins that don’t impair neuromuscular function.

Anti-striated muscle antibody (striated muscle antibody, IgG)

titers greater than or equal to 1:80 are suggestive of myasthenia.

This antibody is detectable in 30% to 40% of anti-AChR-negative

6â•… acetylcholine receptor antibody panel

patients (particularly those with bulbar symptoms only). However,

striated muscle antibody can be found in rheumatic fever, myocardial

infarction, and a variety of postcardiotomy states.

Interfering factors

• False-positive results may occur in patients with amyotrophic

lateral sclerosis who have been treated with cobra venom.

• False-positive results may be seen in patients with penicillamineinduced

or Lambert-Eaton myasthenic syndrome.

• Patients with autoimmune liver disease may have elevated

results.

Drugs that may cause increased levels include muscle paralytic

medicines (succinylcholine) and snake venom.

Immunosuppressive drugs may suppress the formation

of╯these antibodies in patients with subclinical MG.

Procedure and patient care

• See inside front cover for Routine Blood Testing.

• Fasting: no

• Blood tube commonly used: red

Abnormal findings

╇ Increased titer levels

Myasthenia gravis

Ocular myasthenia gravis

Thymoma

notes

acid phosphataseâ•… 7

acid phosphatase╇ (Prostatic acid phosphatase [PAP], A

Tartrate-resistant acid phosphatase [TRAP])

Type of test╇ Blood

Normal findings

Adult/elderly: 0.13-0.63 units/L (Roy, Brower, Hayden; 37â•–°â•›C)

or 2.2-10.5 units/L (SI units)

Child: 8.6-12.6 units/mL (30 °â•›C)

Newborn: 10.4-16.4 units/mL (30 °â•›C)

Test explanation and related physiology

Acid phosphatase is found in many tissues, including liver, red

blood cells, bone marrow, and platelets. The highest levels are

found in the prostate gland—the PAP isoenzyme. Usually (but

not always) elevated levels are seen in patients with prostatic cancer

that has metastasized beyond the capsule to other parts of

the body, especially bone. The degree of elevation indicates the

extent of disease.

Because acid phosphatase is also found at high concentrations

in seminal fluid, this test can be performed on vaginal secretions

to investigate alleged rape. This is now the primary use of PAP

testing. High levels of acid phosphatase also exist in white blood

cells (mostly monocytes and lymphocytes). They are helpful in

determining the clinical course of patients with lymphoproliferative

diseases and hairy cell leukemia. Acid phosphatase is a

lysosomal enzyme. Therefore, lysosomal storage diseases (e.g.,

Gaucher disease and Niemann-Pick disease) are associated with

elevated levels.

Interfering factors

• Alkaline and acid phosphatase are very similar enzymes that

differ in the pH at which they are identified. Any condition

associated with very high levels of alkaline phosphatase may

falsely indicate high acid phosphatase levels.

• Falsely high levels of acid phosphatase may occur in males

after a digital examination or after instrumentation of the

prostate (e.g., cystoscopy) because of prostatic stimulation.

Drugs that may cause increased levels of acid phosphatase

include alglucerase, androgens (in females), and clofibrate.

Drugs that may cause decreased levels include alcohol, fluorides,

heparin, oxalates, and phosphates.

8â•… acid phosphatase

Procedure and patient care

• See inside front cover for Routine Blood Testing.

• Fasting: no

• Blood tube commonly used: red

• Avoid hemolysis. Red blood cells contain acid phosphatase.

• Note on the laboratory slip if the patient has had a prostatic

examination or instrumentation of the prostate within the last

24 hours.

• Do not leave the specimen at room temperature for 1 hour or

longer, because the enzyme is heat- and pH-sensitive and its

activity will decrease.

Abnormal findings

╇ Increased levels

Prostatic carcinoma

Benign prostatic hypertrophy

Prostatitis

Multiple myeloma

Paget disease

Hyperparathyroidism

Metastasis to the bone

Sickle cell crisis

Thrombocytosis

Lysosomal disorders (e.g., Gaucher disease)

Renal diseases

Liver diseases (e.g., cirrhosis)

Rape

notes

activated clotting timeâ•… 9

activated clotting time╇ (ACT, Activated coagulation time) A

Type of test╇ Blood

Normal findings╇ 70-120╛sec

Therapeutic range for anticoagulation: 150-600â•›sec

(Normal ranges and anticoagulation ranges vary according to

type of laboratory procedure and particular therapy.)

Possible critical values╇ Depends upon use for the test and

clinical situation

Test explanation and related physiology

The ACT is primarily used to measure the anticoagulant effect

of heparin or other direct thrombin inhibitors during cardiac

angioplasty, hemodialysis, and cardiopulmonary bypass (CPB)

surgery. This test measures the time for whole blood to clot after

the addition of particulate activators. It is similar to the activated

partial thromboplastin time (APTT, p. 693) in that it measures

the ability of the intrinsic pathway to begin clot formation by

activating factor XII (see Figure€ 10, p. 264). By checking the

blood clotting status with ACT, the response to unfractionated

heparin therapy can be monitored.

Both the APTT and the ACT can be used to monitor heparin

therapy for patients during CPB. However, the ACT has several

advantages over the APTT. First, the ACT is more accurate than

the APTT when high doses of heparin are used for anticoagulation.

This makes it especially useful during clinical situations

requiring high-dose heparin, such as during CPB, when highdose

anticoagulation is necessary at levels 10 times those used for

venous thrombosis. The APTT is not measurable at these high

doses. The accepted goal for the ACT is 400 to 480 seconds

during CPB.

Second, the ACT is both less expensive and more easily performed,

even at the bedside. This allows for immediate accessibility

and decreased turnaround time. The capability to perform the

ACT at the point of care makes the ACT particularly useful for

patients requiring angioplasty, hemodialysis, and CPB.

A nomogram is often used as a guide to reach the desired level

of anticoagulation. This nomogram is used in determining the

dose of protamine to neutralize the heparin upon completion of

these procedures. The ACT is used in determining when it is safe

to remove the vascular access upon completion of these procedures.

The benefits of the modified ACT test are that it requires

a smaller-volume blood specimen; it can be automated; it can use

10â•… activated clotting time

standardized blood/reagent mixing; and it provides faster clotting

time results than the conventional ACT. The modified ACT

is now being used more frequently.

Interfering factors

• The ACT is affected by biologic variables, including hypothermia,

hemodilution, and platelet number and function.

• Factors affecting the pharmacokinetics of heparin (e.g., kidney

or liver disease) and heparin resistance can affect ACT

measurements.

• A clotted specimen can increase ACT measurements.

Procedure and patient care

• See inside front cover for Routine Blood Testing.

• Fasting: no

• Blood tube commonly used: verify with lab

• Less than 1â•›mL of blood is collected and placed in a machine

at the bedside. When a clot forms, the ACT value is displayed.

• If the patient is receiving a continuous heparin drip, the blood

sample is obtained from the arm without the intravenous

catheter.

• The bleeding time will be prolonged because of anticoagulation

therapy.

• Assess the patient to detect possible bleeding. Check for blood

in the urine and all other excretions, and assess the patient for

bruises, petechiae, and low back pain.

Abnormal findings

╇ Increased levels ╇ Decreased levels

Heparin administration Thrombosis

Clotting factor deficiencies

Cirrhosis of the liver

Lupus inhibitor

Warfarin administration

notes

Mosby’s Diagnostic and Laboratory Test Reference 12th edition eBook