NCLEX-RN: Laboratory tests

Laboratory tests: Hematological Tests

Focus topic: Laboratory tests

Laboratory tests: Blood Grouping

Focus topic: Laboratory tests

A. Normal values summary of ABO blood grouping.

B. Purpose—to correctly match donated blood with recipients.

C. Rh blood group.

  •  Positive (85% of the population).
  • Negative (15% of the population).

 

Laboratory tests: Antigens and Antibodies

Focus topic: Laboratory tests

A. Based on type of antigens present in red blood cells as well as type of antibodies in the serum.

B. A and B antigens.

  •  Clients with type A blood have antigen A present; clients with type B blood have antigen B present.
  •  Clients with type AB blood have both A and B antigens present.
  •  Clients with type O blood have no antigens present.

C. Anti-A and anti-B antibodies present.

  •  Clients with type A blood do not have anti-A antibodies because the blood cells would be destroyed by agglutination; they have anti-B antibodies.
  •  Type B blood has anti-A antibodies.

Laboratory tests

Laboratory tests: Blood Coagulation

Focus topic: Laboratory tests

A. Clotting takes place in three phases.

  •  Phase I—prothrombin activator formed in response to ruptured vessel or damage to blood.
  •  Phase II—prothrombin activator catalyzes conversion of prothrombin into thrombin.
  •  Phase III—thrombin acts as an enzyme to convert fibrinogen into fibrin thread.

B. Types of clotting factors.

  • Calcium ions.
    a. Cofactor in coagulation.
    b. Does not enter into reaction.
    c. If absent, neither extrinsic nor intrinsic system will operate.
  •  Phospholipids.
    a. Necessary for formation of final prothrombin activator.
    b. Thromboplastin is phospholipid in extrinsic system.
    c. Platelet factor III is phospholipid for intrinsic system.
  •  Plasma protein all clotting factors from V to XIII.

C. Coagulation mechanisms.

  •  Extrinsic mechanisms.
    a. Extract from damaged tissue is mixed with blood.
    b. Trauma occurs to tissue or endothelial surface of vascular wall, releasing thromboplastin.
  •  Intrinsic mechanisms.
    a. Blood itself comes into contact with roughened blood vessel wall.
    b. Platelets adhere to vessel and disintegrate, which releases blood factor III containing thromboplastin.

D. Fibrinolytic system.

  • Adequate function is necessary to maintain hemostasis.
  • Dissolves clots through formation of plasmin.

Laboratory tests: Prothrombin Time

Focus topic: Laboratory tests

A. Normal values—10–13 seconds (some labs use 11–16 seconds).

B. Purpose—prothrombin time provides data on thrombin generation or how long it takes for a fibrin clot to form after reagent tissue and calcium are added to citrated plasma.

  •  It is a screening test to detect deficiencies in the extrinsic clotting mechanism.
  •  Useful for control of long-term anticoagulant therapy.

C. Critical values.

  • If value is greater than 30 seconds, hemorrhage may occur observe for bleeding.
  •  Administer vitamin K as ordered.

D. Possible causes of prolonged clotting time.

  •  Inadequate vitamin K in premature and newborn infants or in diet.
  • Poor fat absorption (obstructive jaundice).
  •  Liver disease (cirrhosis, hepatitis).
  •  Specific drugs (heparin, Coumadin [warfarin sodium], salicylates [aspirin]).

Laboratory tests: Anti-Factor Xa Activity

Focus topic: Laboratory tests

A. Used to determine the adequacy of anticoagulation in clients receiving agents that interfere with factor Xa activity (e.g., heparin, low-molecular-weight heparin, Xarelto [rivaroxaban], Eliquis [apixaban]).

  •  The direct factor Xa inhibitors (e.g., Xarelto [rivaroxaban], Eliquis [apixaban]) do not require routine monitoring in practice.
  • Two relatively new anticoagulants, low molecular- weight heparin (LMWH) and Orgaran (danaparoid), if present at therapeutic levels, usually do not significantly prolong the activated partial thromboplastin time (APTT). Therefore, when laboratory tests are used to monitor therapeutic anticoagulant levels of LMWH or Orgaran, anti-factor Xa assays are necessary.

B. Purpose: Determine if the client is at the desired level of anticoagulation with therapeutic doses of heparin, LMWH, or Orgaran.

C. Monitoring.

  • Continuous intravenous administration of unfractionated heparin: anti-factor Xa activity can be measured at any time (i.e., as a random level).
  •  Low-molecular-weight heparin (LMWH): anti-factor Xa activity should be tested 4 hours after the dose is administered.
  •  Oral direct anti-Xa drugs can be monitored by anti-factor Xa activity in assays calibrated for he drug; however, there is no established range as these drugs were approved for use without a monitoring requirement.
  •  Results of anti-factor Xa assays may differ between laboratories due to variability in the type of assays used.

D. Normal values.

  •  Clients not on anticoagulants: 0 units/mL.
  •  Therapeutic range for treatment of existing deep venous thrombosis (DVT):
    a. Heparin 0.3–0.7 units/mL.
    b. LMWH: 0.4–1.1 units/mL for twice daily subcutaneous dosing.
    c. For once daily subcutaneous LMWH dosing, the therapeutic range is less certain but is approximately 1–2 units/mL.
    d. Orgaran: 0.5–0.8 units/mL.
  •  Target range for DVT prophylaxis (prevention): There is no defined target range for prophylaxis of DVT because such anticoagulation is not usually monitored. When anti-Xa levels have been measured, mean values have been < 0.45 units/mL.

Laboratory tests: Activated Partial Thromboplastin Time

Focus topic: Laboratory tests

A. Normal values—20–38 seconds with standard technique; different activators will yield different values.

B. Purpose—best single screening test for coagulation disorders.

  •  Test evaluates adequacy of plasma clotting factors intrinsic clotting mechanism.
  •  Test of choice for monitoring heparin therapy.
  •  Used for clients with hemophilia.

C. Arterial values if activated partial thromboplastin time (APTT) is very prolonged (100 seconds), assess for spontaneous bleeding coagulant disorder.

D. Possible causes of prolonged clotting time.

  • Vitamin K deficiency.
  • Liver disease.
  •  Hemophilia.
  •  Specific drugs (heparin, Coumadin [warfarin], salicylates).

E. When APTT is prolonged, MD may order protamine sulfate (or in severe cases, whole blood or plasma transfusion).

Laboratory tests: International Normalized Ratio

Focus topic: Laboratory tests

A. Designed to standardize values and improve monitoring process. Test provides a more accurate assessment of client’s anticoagulant; a uniform value in which client’s PT is expressed as a ratio.

B. Standardizes PT ratio by allowing all thromboplastin reagents to be compared to an international standard thromboplastin (sensitivity index) provided by the World Health Organization (WHO).

  •  International normalized ratio (INR) is a mathematical correction to prothrombin time ratio (PTR).
  •  Value is calculated using client’s PT divided by the mean normal PT. Target range is 2.5 to 3.5.
  •  INR is calculated by raising the observed PT ratio to the power of the sensitivity index, depending on the reagent used.

C. The INR is the best lab value for monitoring anticoagulation therapy; improves the effectiveness of the medication.

D. Should be used only after client has been stabilized on Coumadin (warfarin) (which takes at least a week).

E. Often, both PT and INR values are reported for monitoring Coumadin (warfarin) therapy.

Laboratory tests: Prostate-Specific Antigen Test

Focus topic: Laboratory tests

A. Values.

  • Normal: 0 to 4–6 ng/mL.
  •  Benign prostatic hypertrophy: 4 to 9 ng/mL.
  •  Prostate cancer: 10 to 120 ng/mL.

B. Purpose—shows concentration of glycoprotein from prostate tissue.

  •  Increases with benign prostatic hypertrophy (BPH).
  •  Markedly increases with cancer of the prostate.
  •  Used to diagnose or to monitor effect of treatment with chemotherapy or radiation.
  •  Collect 5 mL of venous blood before rectal or prostate exam (exam irritates tissue).

Laboratory tests: Serum Protein Electrophoresis Test

Focus topic: Laboratory tests

A. Normal values:

  •  Total serum protein: 6.3 to 7.9 g/dL.
  •  Albumin: 3.5 to 5.0 g/dL.
  •  Alpha1 globulin: 0.1 to 0.4 g/dL.
  • Alpha2 globulin: 0.4 to 1.0 g/dL.
  •  Beta globulin: 0.5 to 1.1 g/dL.
  •  Gamma globulin: 0.5 to 1.7 g/dL.

B. Purpose: To differentiate between protein fractions  serum proteins are made up of albumin and globulins. Test indicates the size, shape, and electrical charge of the major blood proteins (fractions) to diagnose certain diseases.

C. Abnormal results.

  • Elevated levels.
    a. Albumin: dehydration, exercise.
    b. Alpha1 and alpha2, globulins: myocardial infarction, hepatic disease, myeloma, collagen diseases, and acute and chronic infections.
  •  Decreased levels: liver disease, malnutrition, leukemia, renal failure, emphysema, anemia.

Laboratory tests: Renal Function Tests

Focus topic: Laboratory tests

A. Phenolsulfonphthalein (PSP) test indicates the functional ability of the kidney to

  •  Excrete waste products.
  •  Concentrate and dilute urine.
  •  Carry on absorption and excretion activities.
  •  Maintain body fluids and electrolytes.

B. Renal concentration tests.

  • Evaluate the ability of the kidney to concentrate urine.
  • As kidney disease progresses, renal function decreases. Concentration tests evaluate this process.
  • Renal concentration is measured by specific gravity readings.

C. Specific gravity.

  • Normal value range is 1.003–1.030, usually 1.010–1.025.
  • If specific gravity is 1.018 or greater, it may be assumed that the kidney is functioning within normal limits.
  • Specific gravity that stabilizes at 1.010 indicates kidney has lost ability to concentrate or dilute urine.

D. Blood urea nitrogen (BUN).

  • Normal value—10–20 mg/100 dL.
  • Purpose—tests for impaired kidney function by testing the body’s urea production and urine flow.
  • BUN level affected by protein intake and tissue breakdown.

E. Serum creatinine.

  •  Normal value male: 0.8–1.2 mg/dL; female: 0.6–0.9 mg/dL. If normal value doubles, overall renal function and glomerular  filtration rate (GFR) have decreased by half.
    a. When elevated, suggests hypertension or drugs such as steroids.
    b. Decreased indicates mild to severe renal impairment, muscular dystrophy, or use of certain drugs.
  •  Purpose tests renal function by evaluating the balance between production and filtration of glomeruli.
  • This is the most sensitive of renal function tests.

F. Concentration and dilution tests.

  •  Fishberg concentration test—high-protein dinner with 200 mL fluid is ordered. Next am on arising, client voids q 1/hr. One specimen should have specific gravity more than 1.025.
  •  Dilution test—NPO after dinner. Morning voiding discarded. Client drinks 1000 mL in 30 to 45 minutes. Four specimens at 1-hour intervals are collected. Specific gravity of one specimen will fall below 1.003.
  • Specific gravity—urine range 1.003 to 1.030. Increased solutes cause increased specific gravity (see above).

G. Glomerular filtration rate (GFR) or endogenous creatinine clearance.

  • Normal values 125 mL/min (male) and 110 mL/min (female).
  • Purpose—kidney function is assessed by clearing a substance from the blood such as inulin, a polysaccharide found in      plants (filtration in the glomerulus).
  • Common test is the amount of blood cleared of urea per minute.
  • Test done on 12- or 24-hour urine specimen.

H. Electrolyte tests.

  • Kidney function is essential to maintain fluid and electrolyte balance.
  • Tests for electrolytes (sodium, potassium, chloride, and bicarbonate) measure the ability of the kidney to filter, reabsorb, or excrete these substances.
  • Impaired filtration leads to retention, and impaired reabsorption leads to loss of electrolytes.
  • Tests are performed on blood serum, so venous blood is required.

Laboratory tests: Urine Analysis

Focus topic: Laboratory tests

A. Normal values.

  •  Specific gravity—1.010–1.025.
  •  Urine pH—4.5–8.0.
  •  Color—straw.
  •  Odor—aromatic.
  •  Appearance—clear.
  •  Protein—negative or zero.
  • Glucose—negative or zero.
  • Ketones—negative or zero.
  • Red blood cells—0–3.
  • White blood cells—0–4.
  •  Casts—none; occasional.
  •  Crystals—negative.
  •  Yeast cells—none.
  •  Parasites—none.

B. Urinalysis is a critical test for total evaluation of the renal system and for indication of renal disease.

C. Specific gravity shows the degree of concentration in urine.

  •  Normal value—1.010–1.025.
  •  Indicates the ability of the kidney to concentrate or dilute urine.
  •  Change from normal range.
    a. Elevated (greater than 1.030) indicates fluid depletion—diabetes mellitus, dehydration, vomiting/diarrhea, contrast media (1–2 days).
    b. Low (less than 1.010) indicates fluid excess diabetes insipidus, overhydration, renal disease.
  • Renal failure—specific gravity constant at 1.010.

D. Analysis of urine pH.

  • pH is the symbol for the logarithm of the reciprocal of the hydrogen ion concentration.
  • A measurement of hydrogen ion concentration is taken—the lower the number, the higher the acidity of urine.
    a. Normal value range—4.5 to 8.0 (normal pH is 6 to 7).
    b. Lower than 6 is acidic urine, and higher than 7 is alkaline urine.
  • Regulation of urine pH is important for treatment of certain conditions.
    a. When the pH is alkaline, it suggests urinary tract infection, metabolic or respiratory alkalosis, drug influence, a vegetarian  or highly alkaline diet.
    b. When the pH is acidic, it may reflect renal tuberculosis (TB), phenylketonuria (PKU), pyrexia, acidosis.
    c. Acid urine may be desired when treating blood infections or phosphate stones.

E. Chemical analysis of urine.

  •  Protein or albumin—zero is normal for a 24-hour specimen.
    a. Presence may indicate kidney dysfunction or renal disease, such as nephritis or nephrosis.
    b. Inflammatory processes any place in the body may result in proteinuria.
    c. Toxemia of pregnancy yields a finding of proteinuria.
    d. Renal calculi indicate positive test results.
    e. Appearance in urine may be due to dehydration, strenuous exercise, high-protein diet.
  • Glucose normal range is zero.
    a. Presence of glucose may indicate head injury, diabetes, Cushing’s syndrome, hyperthyroidism.
  • b. Test is usually done by test strips or tablets; change in color indicates presence of glucose. (Urine testing for glucose has been primarily replaced by testing blood for glucose.)
  •  Ketone bodies normal range is zero. Positive is +1 to +3.
    a. Ketonuria primarily indicates diabetic acidosis but is also present with starvation and pernicious vomiting.
    b. Test is usually done by strip or powder mixed with urine; purple color indicates positive test.
  •  Bilirubin normal range is zero.
    a. Presence in urine may indicate liver disease and may appear before the clinical symptom of jaundice.
    b. Detected in the urine by qualitative methods, such as inspection of color.
  •  Blood normal range is zero.
    a. If red blood cells are present, may indicate disease of kidney or urinary tract, and the source of hemorrhage must be determined.
    b. Specific diagnosis is made by complete urine analysis for casts and epithelial cells.

F. Microscopic examination of urine.

  •  Evaluation of urinary sediment is important for diagnostic purposes.
  •  Test for cellular elements (epithelial cells, white and red blood cells).
  •  Test for casts, fat bodies, and crystals.

G. Levels of albuminuria.

  •  30 mg/100 mL = 1+.
  • 100 mg/100 mL = 2+.
  • 300 mg/100 mL = 3+.
  •  1000 mg/100 mL = 4+.

Laboratory tests: Schilling Urine Test

Focus topic: Laboratory tests

A. Determines absorption of vitamin B12 necessary for erythropoiesis—definitive test for pernicious anemia and intestinal malabsorption syndrome.

B. 7% excretion of radioactive B12 in urine within 24 hours. (When less than 3 g is excreted, diagnosis is confirmed.)

Laboratory tests: Analysis of GI Secretions

Focus topic: Laboratory tests

A. Contents of the GI tract may be examined for the presence or absence of digestive juices, bacteria, parasites, and malignant cells.

B. Stomach contents may be aspirated and analyzed for volume and free and total acid.

Laboratory tests: Gastric Analysis

Focus topic: Laboratory tests

A. Performed by means of a nasogastric tube.

  •  Maintain NPO 6–8 hours prior to the test.
  •  Pass NG tube; verify its presence in the stomach; tape to client’s nose.

B. Collect fasting specimens.

  •  Administer agents, such as alcohol, caffeine, histamine (0.2 mg subcutaneous), as ordered, to stimulate the flow of gastric acid.
    a. Watch for side effects of histamine, including flushing, headache, and hypotension.
    b. Do not give drug to clients with a history of asthma or other allergic conditions.
  • Collect specimens as ordered, usually at 10- to 20-minute intervals.
  •  Label specimens and send to laboratory.
  • Withdraw NG tube; offer oral hygiene; make client comfortable.
  •  Gastric acid is high in the presence of duodenal ulcers and is low in pernicious anemia.

C. Gastric washings for acid-fast bacilli.

  •  Instruct client to fast 6–8 hours prior to the procedure.
  •  Insert nasogastric tube and secure gastric washings.
  •  Send specimens to the laboratory to determine the presence of acid-fast bacilli.
  •  Wash your hands carefully and protect yourself from direct contact with specimens.
  • This procedure is performed on suspected cases of active pulmonary tuberculosis when it is difficult to secure sputum for analysis.

Laboratory tests: Stool Analysis

Focus topic: Laboratory tests

A. Stool specimens are examined for amount, consistency, color, shape, blood, fecal urobilinogen, fat, nitrogen, parasites, food residue, and other substances.

  •  Stool cultures are also done for bacteria and viruses.
  •  Some foods and medicines can affect stool color spinach, green; cocoa, dark red; senna, yellow; iron, black; upper GI bleeding, tarry black; lower GI bleeding, bright red.

B. Stool abnormalities.

  • Steatorrhea—bulky, greasy and foamy, foul odor.
  •  Biliary obstruction—light gray or clay-colored.
  •  Ulcerative colitis—loose stools, with copious amounts of mucus or pus.
  •  Constipation or obstruction—small, hard masses.

C. Specimen collection.

  •  Specimens for detection of ova and parasites should be sent to the laboratory while the stool is still warm and fresh.
  •  Examinations for blood are performed on small samples. A tongue blade may be used to place a small amount of stool in a disposable waxed container, or place a drop on a commercial card, which will turn color if blood is present in the stool.
  •  Stools for chemical analysis are usually examined for the total quantity expelled, so the complete stool is sent to the laboratory.

Laboratory tests: Liver Function Tests

Focus topic: Laboratory tests

A. Pigment studies.

  •  Serum bilirubin—abnormal in biliary and liver disease causing jaundice.
    a. Direct (conjugated)—normal: 0–0.3 mg/100 mL, soluble in H2O.
    b. Indirect (unconjugated)—normal: 0.8–1.0 mg/100 mL, insoluble in H2O.
    c. Total serum bilirubin—normal: 0–0.9 mg/100 mL.
  •  Urine bilirubin—normally none is found.
  •  Urine urobilinogen—0–4 mg/24 hours.
  •  Fecal urobilinogen—40–280 mg/24 hours.
  • Serum cholesterol—150–250 mg/100 mL.

B. Protein studies.

  • Total protein—6–8 g/100 mL.
  •  Serum albumin—3.5–5.0 mg/100 mL.
  •  Serum globulin—1.5–3.0 mg/100 mL.
  •  Prothrombin time—11–15 seconds.
  •  Cephalin—0–1+.
  •  In liver damage, fewer plasma proteins are synthesized; thus albumin synthesis is reduced.
    a. Serum globulins produced by the plasma cells are increased.
    b. PT is reduced in liver cell damage.
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C. Cholesterol

D. Detoxification.

  •  Bromsulphalein excretion (BSP).
  •  Less than 5% dye retention after 1 hour.
    a. Dye is injected intravenously and removed by the liver cells, conjugated, and excreted.
    b. Blood specimen is obtained at 30-minute and 1-hour intervals after injection.
    c. Increased retention occurs in hepatic disorders.

E. Enzyme (transaminase) indicators.

  •  Elevations reflect organ damage.
  •  Levels.
    a. AST (formerly SGOT)—10–40 units/mL

b. Alanine transaminase (ALT) (formerly serum glutamic pyruvic transaminase [SGPT])—5–35 units/mL.
c. LDH—100–200 units/mL.
d. Gamma-glutamyl transpeptidase (GGT)— 10–48 units/mL.

F. Alkaline phosphatase.

  •  2–5 units (varies with method used).
  •  Elevated in obstructive jaundice, liver disease, Paget’s disease, and cancer with bone metastasis.

G. Blood ammonia.

  •  20–120 μg/dL.
  •  Ammonia level rises in liver failure because liver converts ammonia to urea.
  •  Metabolic alkalosis increases the toxicity of NH3.
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