Clinician's Pocket Reference: The Scut Monkey, 11e >

Chapter 6. Laboratory Diagnosis: Urine Studies

Figure 6–1.

Urinalysis Procedure

For routine urinalysis, a fresh (less than 1-h old), clean-catch urine sample is acceptable. If the analysis cannot

be performed immediately, refrigerate the sample. (When urine stands at room temperature for a long time,

casts and red cells undergo lysis, and the urine becomes alkalinized with precipitation of salts.) See Chapter

13, Urinary Tract Procedures, for sample collection.

• 1. Pour 5–10 mL of well-mixed urine into a centrifuge tube.

• 2. Check for appearance (color, turbidity, odor). If a urine sample looks grossly cloudy, it is sometimes

advisable to examine an unspun sample. If you use an unspun sample, make a note that you have done

so. In general, a spun sample is more desirable for routine urinalysis.

• 3. Spin the capped sample at 3000 rpm (450g) for 3–5 min.

• 4. While the sample is in the centrifuge, use the dipstick (eg, Chemstrip) supplied by your lab to perform

the dipstick evaluation on the remaining sample. Read the results according to the color chart on the

bottle. Allow the correct amount of time before reading the test (usually 1–2 min) to avoid false results.

Chemstrip 10 provides 10 tests (specific gravity, pH, leukocytes, nitrite, protein, glucose, ketone,

urobilinogen, bilirubin, and blood.) Other strips may provide less.) Agents that color the urine

(phenazopyridine [Pyridium]) may interfere with the reading. Dipstick specific gravity (SG)

measurement is possible, but a refractometer also can be used to determine SG.

• 5. Decant and discard the supernatant. Mix the remaining sediment by flicking it with a finger and

pouring or pipetting one or two drops onto a microscope slide. Cover with a coverslip.

• 6. Examine 10 low-power fields (10× objective) for epithelial cells, casts, crystals, and mucus. Casts are

usually reported as number per low-power field and tend to collect around the periphery of the coverslip.

• 7. Examine several high-power fields (40× objective) for epithelial cells, crystals, RBCs, WBCs,

bacteria, and parasites (trichomonads). RBCs, WBCs, and bacteria are usually reported as number per

high-power field. The following two reporting systems are commonly used:

System One System Two

Rare = < 2/field Trace = <¼ of field

Occasional = 3–5/field 1+ = ¼ of field

Frequent = 5–9/field 2+ = ½ of field

Many = “large number”/field 3+ = ¾ of field

TNTC = too numerous to count 4+ = field is full

Urinalysis, Normal Values

• 1. Appearance: “Dark yellow or amber in color and clear”

2. Specific Gravity

◦ a. Neonates: 1.012

b. Infants: 1.002–1.006

c. Children and Adults: 1.001–1.035 (typical with normal fluid intake 1.016–1.022)

3. pH

◦ a. Neonates: 5–7

b. Children and Adults: 4.6–8.0

4. Negative for: Bilirubin, blood, acetone, glucose, protein, nitrite, leukocyte esterase, reducing

substances

5. Trace: Urobilinogen

6. RBC: Male 0–3/hpf, female 0–5/hpf

7. WBC: 0–4/hpf

8. Epithelial Cells: Occasional

9. Hyaline Casts: Occasional

10. Bacteria: None

11. Crystals: Some limited crystals based on urine pH (see Differential Diagnosis for Routine

Urinalysis)

Differential Diagnosis for Routine Urinalysis

Appearance

• Colorless: Diabetes insipidus, diuretics, excess fluid intake

• Dark: Acute intermittent porphyria, advanced malignant melanoma

• Cloudy: UTI (pyuria), amorphous phosphate salts (normal in alkaline urine or urine left standing at

room temperature. Adding a small amount of acid to the sample will confirm), blood, mucus, bilirubin

• Pink/Red:

• Heme(+). Blood, Hbg, sepsis, dialysis, myoglobin

• Heme(–). Food coloring, beets, sulfa drugs, nitrofurantoin, salicylates

• Orange/Yellow: Dehydration, phenazopyridine (Pyridium), rifampin, bile pigments

• Brown/Black: Myoglobin, bile pigments, melanin, cascara, iron, nitrofurantoin, alkaptonuria

• Green/Blue: Urinary bile pigments, indigo carmine, methylene blue

• Foamy: Proteinuria, bile salts

Bilirubin

Limited utility on dipstick

Positive:

(Only conjugated bilirubin appears in urine) Obstructive jaundice (intrahepatic and extrahepatic), hepatitis.

False-positive with stool contamination

Blood (Hematuria)

If the dipstick is positive for blood, but no red cells are seen, free Hbg may be present (transfusion reaction,

from lysis of RBCs if pH is < 5 or > 8) or myoglobin is present (crush injury, burn, or tissue ischemia).

Positive:

Stones, trauma, tumors (benign and malignant, anywhere in the urinary tract), BPH, urethral stricture,

coagulopathy, infection, menses (contamination), polycystic kidneys, interstitial nephritis, hemolytic anemia,

transfusion reaction, instrumentation (eg, Foley catheter)

Glucose

Glucose oxidase technique in most kits is specific for glucose and does not react with lactose, fructose, or

galactose; therefore screen infant urine with another assay such as Clinitest.

Positive:

DM, pancreatitis, pancreatic carcinoma, pheochromocytoma, Cushing disease, shock, burns, pain, steroids,

hyperthyroidism, renal tubular disease, iatrogenic causes; false-positive: uncapped dipstick container bottle

after several days, specimen contamination with liquid bleach

Ketones

Used primarily to detect acetone and acetoacetic acid and not β-hydroxybutyric acid

Positive:

Starvation, high-fat diet, DKA, vomiting, diarrhea, hyperthyroidism, PRG, febrile state (especially in children),

aspirin overdose; false-positive: some Parkinson medications, cystinuria, stimulant laxative (such as Ex-Lax)

Leukocyte Esterase

Used to detect 5 WBCs/hpf or lysed WBCs. Combined with the nitrite test, leukocyte esterase has a positive

predictive value of 74% for UTI if both tests are positive and a negative predictive value of > 97% if both tests

are negative. May not be reliable in children with UTI

Positive:

UTI (false-positive: vaginal/fecal contamination; pediatric urine bag collection)

Nitrite

Many bacteria convert nitrates to nitrite. (See Leukocyte Esterase, and see Chapter 7)

Positive:

Infection (negative test does not exclude infection because some organisms [Streptococcus faecalis, other

gram-positive cocci], do not produce nitrite, and urine must be in the bladder for several hours to allow the

nitrite reaction to take place)

Odor

Limited utility: strong ammonia smell suggests UTI; asparagus consumption

pH

Acidic:

High-protein (meat) diet, ammonium chloride, mandelic acid and other medications, acidosis (due to

ketoacidosis [starvation, diabetic], COPD)

Basic:

UTI, RTA, diet (high-vegetable diet, milk, immediately after meals), sodium bicarbonate therapy, vomiting,

metabolic alkalosis

Protein

Proteinuria on dipstick should be quantified with 24-h urine studies. Normal protein excretion is < 150 mg/24

h or 10 mg/100 mL in a spot specimen (dipstick approximations: Negative, 0–50; trace, 50–150; 1+, 150–300;

2+, 300–1000; 3+, 1–3; 4+, > 3 gm/L). Bence Jones globulins (plasma cell myeloma, macroglobulinemia;

lymphoma may be missed on dipstick and determined on urine protein electrophoresis).

Positive:

Pyelonephritis, glomerulonephritis, glomerular sclerosis (diabetes), nephrotic syndrome, myeloma, postural

causes, preeclampsia, inflammation and malignant diseases of lower urinary tract, functional causes (fever,

stress, heavy exercise), malignant hypertension, CHF

Reducing Substances

Positive:

Glucose, fructose, galactose, false-positives (eg, vitamin C, salicylates, antibiotics)

Specific Gravity

Corresponds with osmolarity except with osmotic diuresis (high glucose). Random value 1.003–1.030. Value >

1.022 after 12 h food/fluids fast suggests normal renal concentrating ability. Isosthenuria (SG fixed at 1.010

regardless of intake) suggests renal tubular dysfunction.

Increased:

Volume depletion, CHF, adrenal insufficiency, DM, SIADH, increased proteins (nephrosis), newborn state; if

markedly increased (1.040–1.050), artifact or recent administration of radiographic contrast media

Decreased:

Diabetes insipidus, pyelonephritis, glomerulonephritis, water load with normal renal function (note effective

management in kidney stone patients, hydrate to keep SG very low)

Urobilinogen

Limited utility on dipstick (Note: Urobilinogen is colorless)

Positive:

Hemolysis, cirrhosis, CHF with hepatic congestion, hepatitis, hyperthyroidism, suppression of intestinal flora

with antibiotics

Urine Sediment

Many labs no longer do microscopic examinations unless requested or if there is an abnormal dipstick test

result.

Figure 6–1 is a diagram of materials found in urine sediments.

Figure 6–1.

Urine sediment as seen with a microscope. (Reproduced, with permission, from: Greene MG [ed]: The Harriet

Lane Handbook: A Manual for Pediatric House Officers, 12th ed., Year Book Medical Publishers, Chicago,

IL, 1991.)

Red Blood Cells (RBCs):

Trauma, pyelonephritis, genitourinary TB, cystitis, prostatitis, stones, tumors (malignant and benign),

coagulopathy, and any cause of blood on dipstick test (see Differential Diagnosis for Routine Urinalysis,

Blood)

White Blood Cells (WBCs):

Infection anywhere in the urinary tract, TB, renal tumors, acute glomerulonephritis, radiation, interstitial

nephritis (analgesic abuse)

Epithelial Cells:

ATN, necrotizing papillitis. (Most epithelial cells are from an otherwise unremarkable urethra.)

Parasites:

Trichomonas vaginalis, Schistosoma haematobium infection

Yeast:

Candida albicans infection (especially in diabetic or immunosuppressed patients or if a vaginal yeast infection

is present)

Spermatozoa:

Normal in men immediately after intercourse or nocturnal emission

Crystals

• Normal

• Acidic urine: Calcium oxalate (small, square crystals with a central cross; octahedrons), uric acid

(rhomboids, hexagons, squares)

• Alkaline urine: Calcium carbonate/phosphate, triple phosphate (struvite, magnesium ammonium

phosphate associated with urea-splitting UTI and possible stone formation [coffin lids])

• Abnormal

• Any: Cystine (colorless hexagons), sulfonamide, leucine (bicycle wheels), tyrosine, cholesterol

• Excessive: Calcium oxylate (excess vitamin C or spinach, ileitis, ethylene glycol poisoning, urolithiasis),

uric acid (gout, leukemia, tumor lysis during chemotherapy), triple phosphate (urea splitting UTI and

with “infection” stone formation), indinavir (crystals in patients on HIV therapy)

Contaminants:

Cotton threads, hair, wood fibers, amorphous substances (all usually unimportant); “dirty urine” may suggest

enterovesical fistula

Mucus:

Large amounts of mucus suggest urethral disease (normal from ileal conduit or continent urinary diversion that

uses bowel) or enterovesical fistula.

Glitter Cells:

WBCs lysed in hypotonic solution

Casts:

Localizes some or all of the disease process to the kidney itself

• Hyaline Casts. Acceptable unless “numerous,” benign hypertension, nephrotic syndrome, after exercise

• RBC Casts. Acute glomerulonephritis, lupus nephritis, SBE, Goodpasture disease, aftermath of

streptococcal infection (poststreptococcal glomerulonephritis), vasculitis, malignant hypertension

• WBC Casts. Pyelonephritis, acute interstitial nephritis, glomerulonephritis

• Epithelial (Tubular) Casts. Tubular damage, nephrotoxin, virus

• Granular Casts. Breakdown of cellular casts, leads to waxy casts; “dirty brown granular casts” typical

for ATN

• Waxy Casts. All cellular casts can become waxy casts. Severe chronic renal disease, amyloidosis

• Fatty Casts. Nephrotic syndrome, DM, damaged renal tubular epithelial cells

• Broad Casts. Chronic renal disease

Spot or Random Urine Studies

A spot urine, which is often ordered to aid in the diagnosis of various conditions, is done with only a small

sample (10–20 mL) of urine.

Spot Urine for β2-Microglobulin

• < 1 mg/24 h or 0–160 g/L (keep sample refrigerated) • A marker of renal tubular injury

Increased:

Diseases of the proximal tubule (ATN, interstitial nephritis, pyelonephritis), viral diseases, drug-induced

nephropathy (aminoglycosides), diabetes, trauma, sepsis, HIV, lymphoproliferative and lymphodestructive

diseases (multiple myeloma, plasmacytoma)

Spot Urine for Cytology

Used as an adjunct in the diagnosis of urothelial cancers (primarily transitional cell carcinoma of the bladder,

kidney and ureter); limited or no role for renal cell carcinoma. Use a 3-h postvoid and not an am sample.

Spot Urine for Electrolytes

Utility is limited because of variations in daily fluid and salt intake; not useful if a diuretic has been taken.

• 1. Sodium < 10 mEq/L: Volume depletion, hyponatremic states, prerenal azotemia (eg, CHF, shock),

hepatorenal syndrome, glucocorticoid excess

• 2. Sodium > 20 mEq/L: SIADH, ATN (usually > 40 mEq/L), postobstructive diuresis, high salt intake,

Addison disease, hypothyroidism, interstitial nephritis

• 3. Chloride < 10 mEq/L: Chloride-sensitive metabolic alkalosis (vomiting, excessive diuretic use),

volume depletion

• 4. Potassium < 10 mEq/L: Hypokalemia, potassium depletion, extrarenal loss

Spot Urine for Erythrocyte Morphology

The morphology of red cells in a urine sample positive for blood may indicate of the nature of the hematuria.

Eumorphic red cells are seen in postrenal, nonglomerular bleeding. Dysmorphic red cells are associated with

glomerular causes of bleeding. Labs vary, but > 90% dysmorphic erythrocytes with asymptomatic hematuria

indicates a renal glomerular source of bleeding, especially if associated with proteinuria or casts (eg, IgA

nephropathy, poststreptococcal glomerular disease, sickle cell disease or trait). If there are 90% eumorphic

erythrocytes or even “mixed” results (10–90% eumorphic erythrocytes), a postrenal cause of hematuria

requires urologic evaluation (eg, hypercalciuria, urolithiasis, cystitis, trauma, tumors, hemangioma, exercise

induced, BPH).

Spot Urine for Microalbumin

Normal < 30 mcg albumin/mg creatinine (timed collection < 20 mcg/min)

Used to determine whether a diabetic patient is at risk of nephropathy or cardiovascular disease. Perform two

or three separate determinations over 6 mo to confirm; spot urine preferred. Diabetic patients with a level of 30

–300 mcg often need an ACE inhibitor or angiotensin receptor blocker. Six percent of the healthy population

has microalbuminuria. The following are the ranges for microalbuminuria recommended by the American

Diabetes Association:

Category Spot Collection (mcg/mg Cr) 24-h Collection (mg/24 h) Timed Collection (mcg/min)

Normoalbuminuria < 30 < 30 < 20

Microalbuminuria 30–299 30–299 20–199

Macroalbuminuria ≥ 300 ≥ 300 ≥ 200

Category Spot Collection (mcg/mg Cr) 24-h Collection (mg/24 h) Timed Collection (mcg/min)

Reproduced, with permission, from the American Diabetes Association, Diabetes Care 2004;27:S15–S35.

Spot Urine for Myoglobin

• Qualitative negative

Positive:

Skeletal muscle conditions (crush injury, electrical burns, carbon monoxide poisoning, delirium tremens,

surgical procedures, malignant hyperthermia), polymyositis

Spot Urine for Osmolality

• 75–300 mOsm/kg, varies with water intake

Patients with normal renal function should concentrate > 800 mOsm/kg after 14-h fluid restriction; < 400

mOsm/kg is a sign of renal impairment.

Increased:

Dehydration, SIADH, adrenal insufficiency, glycosuria, high-protein diet

Decreased:

Excessive fluid intake, diabetes insipidus, acute renal failure, medications (acetohexamide, glyburide, lithium)

Spot Urine for Protein

• Normal < 10 mg/dL (0.1 g/L) or < 20 mg/dL (0.2 g/L) for a sample taken in the early am

See Differential Diagnosis for Routine Urinalysis, Protein.

Creatinine Clearance

Normal

• Men. Total creatinine 1–2 g/24 h; clearance 85–125 mL/min/1.73 m2

• Women. Total creatinine 0.8–1.8 g/24 h; clearance 75–115 mL/min 1.73 m2

• Children. Total creatinine (> 3 y) 12–30 mg/kg/24 h; clearance 70–140 mL/min/1.73 m2 (1.17–2.33

mL/s/1.73 m2)

Decreased:

Decreased creatinine clearance results in an increase in serum creatinine usually secondary to renal

insufficiency. See Chapter 4, Creatinine, Serum (SCR), for differential diagnosis of increased serum creatinine.

Increased:

Early DM, PRG

Methods for Determination of Creatinine Clearance (CrCl)

CrCl is a sensitive indicator of early renal insufficiency. Clearances are ordered for evaluation of patients with

suspected renal disease and monitoring of patients taking nephrotoxic medications (eg, gentamicin). CrCl

decreases with age; CrCl of 10–20 mL/min indicates severe renal failure and usually the need for dialysis.

• 1. Formal 24-h Urinary Collection for Creatinine Clearance. Order a concurrent SCr and a 24-h

urine creatinine. A shorter time interval can be used (eg, 12 h), but the formula must be corrected for this

change; a 24-h sample is less prone to collection error.

Example:

The following are calculations of (a) CrCl from a 24-h urine sample with a volume of 1000 mL, (b) a urine

creatinine of 108 mg/100 mL, and (c) a SCr of 1 mg/100 mL (1 mg/dL).

To determine whether there is a valid, full 24-h collection, the sample should contain 18–25 mg/kg/24 h of

creatinine for men or 12–20 mg/kg/24 h for women. If the patient is an adult (150 lb = body surface area of

1.73 m2

), clearance is not routinely adjusted for body size. Adjustment must be made for pediatric patients.

If the values in the previous example are for a 10-year-old boy weighing 70 lb (1.1 m2), the clearance is:

• 2. Estimated Creatinine Clearance. Online calculators for adults and children are available at:

www.nkdep.nih.gov/professionals/gfr_calculators (Accessed May 29, 2006)

Adults:

• Modification of Diet in Renal Disease (MDRD) equation (Ann Intern Med 1999;130:137–147). The

equation does not require weight; results normalized to 1.732 BSA, an accepted adult average BSA.

Cockcroft-Gault equation:

Children:

Use the Schwartz equation:

where k is a constant (0.33, premature infants; 0.45, term infants to 1 y; 0.55, children to 13 y; 0.65, male

adolescents; 0.55, female adolescents), height is in centimeters, and SCr is in mg/dL.

24-Hour Urine Studies

Many diseases, most of them endocrine, can be diagnosed with assays of 24-h urine samples.

Calcium, Urine

Normal:

On a calcium-free diet < 150 mg/24 h, average-calcium diet (600–800 mg/24 h) 100–250 mg/24 h

Increased:

Hyperparathyroidism, hyperthyroidism, hypervitaminosis D, distal RTA (type I), sarcoidosis, immobilization,

osteolytic lesions (bony metastasis, multiple myeloma), Paget disease, glucocorticoid excess, immobilization,

furosemide

Decreased:

Medications (thiazide diuretics, estrogens, oral contraceptives), hypothyroidism, renal failure, steatorrhea,

rickets, osteomalacia

Catecholamines, Fractionated

Used to evaluate neuroendocrine tumors, including pheochromocytoma and neuroblastoma. Avoid caffeine

and methyldopa (Aldomet) before test.

Normal:

Values are variable and depend on the assay method used. Norepinephrine 15–80 mg/24 h, epinephrine 0–20

mg/24 h, dopamine 65–400 mg/24 h

Increased:

Pheochromocytoma, neuroblastoma, epinephrine administration, presence of drugs (methyldopa, tetracyclines

cause false increases)

Cortisol, Free

Used to evaluate adrenal cortical hyperfunction, screening test of choice for Cushing syndrome

Normal:

10–110 mg/24 h

Increased: Cushing syndrome (adrenal hyperfunction), stress during collection, oral contraceptives, PRG

Creatinine

• See Creatinine, Serum (SCr) and Creatinine Clearance.

Cysteine

Used to detect cystinuria, homocystinuria, monitor response to therapy

Normal:

40–60 mg/g creatinine

Increased:

Heterozygotes < 300 mg/g creatinine; homozygotes > 250 mg/g creatinine

5-HIAA (5-Hydroxyindoleacetic Acid)

5-HIAA is a serotonin metabolite useful in the diagnosis of carcinoid syndrome.

Normal:

2–8 mg /24-h urine collection

Increased:

Carcinoid tumors (except rectal), certain foods (banana, pineapple, tomato, walnuts, avocado), phenothiazine

derivatives

Metanephrines

Used to detect metabolic products of epinephrine and norepinephrine, primary screening test for

pheochromocytoma

Normal:

< 1.3 mg/24 h for adults, but variable in children

Increased:

Pheochromocytoma, neuroblastoma (neural crest tumors), false-positive with drugs (phenobarbital,

guanethidine, hydrocortisone, MAO inhibitors)

Protein

• See also Urine Protein Electrophoresis.

Normal:

< 150 mg/24 h

Increased:

Nephrotic syndrome usually associated with > 3.5 g/1.73 m2/24 h

17-Ketogenic Steroids (17-KGS, Corticosteroids)

Overall adrenal function test, largely replaced by serum or urine cortisol levels

Normal:

Men 5–24 mg/24 h; women 4–15 mg/24 h

Increased:

Adrenal hyperplasia (Cushing syndrome), adrenogenital syndrome

Decreased:

Panhypopituitarism, Addison disease, acute steroid withdrawal

17-Ketosteroids, Total (17-KS)

Used to measure DHEA, androstenedione (adrenal androgens); largely replaced by assay of individual

elements

Normal:

Men 8–20 mg/24 h; women 6–15 mg/dL. Note: Low values in prepubertal children

Increased:

Adrenal cortex abnormalities (hyperplasia [Cushing disease], adenoma, carcinoma, adrenogenital syndrome),

severe stress, ACTH or pituitary tumor, testicular interstitial tumor and arrhenoblastoma (both produce

testosterone)

Decreased:

Panhypopituitarism, Addison disease, castration in men

Vanillylmandelic Acid (VMA)

VMA is the urinary product of both epinephrine and norepinephrine; good screening test for

pheochromocytoma, also used to diagnose and follow up neuroblastoma and ganglioneuroma

Normal:

< 7–9 mg/24 h

Increased:

Pheochromocytoma, other neural crest tumors (ganglioneuroma, neuroblastoma), factitious causes (chocolate,

coffee, tea, methyldopa)

Other Urine Studies

Drug Abuse Screen

• Normal = negative

Test for common drugs of abuse, often used for employment screening for critical jobs. Assay varies by

facility and may include tests for amphetamines, barbiturates, benzodiazepines, marijuana (cannabinoid

metabolites), cocaine metabolites, opiates, phencyclidine.

Xylose Tolerance Test (D-Xylose Absorption Test)

• 5 g xylose in 5-h urine specimen after 25-g oral dose of xylose or 1.2 g after 5-g oral dose • Collection:

Patient is on NPO status after midnight except for water

• After 8 am void, 25 g of d-xylose (or 5 g if GI irritation is a concern) is dissolved in 250 mL water • Patient

drinks an additional 750 mL water, and urine is collected for the next 5 h.

Used to assess proximal bowel function; differentiates malabsorption due to pancreatic insufficiency and that

due to intestinal problems

Decreased:

Celiac disease (nontropical sprue, gluten-sensitive enteropathy), false decrease with renal disease

Urinary Indices in Renal Failure

Use Table 6–1 to differentiate the causes (renal or prerenal) of oliguria. (See also Oliguria and Anuria.)

Table 6–1 Urinary Indices Useful in the Differential Diagnosis of Oliguria

Index Prerenal Renal (ATN)a

Urine osmolality >500 <350

Urinary sodium <20 >40

Urine/serum creatinine >40 <20

Urine/serum osmolarity >1.2 <1.2

Fractional excreted sodiumb <1 >1

Renal failure index (RFI)c <1 >1

aAcute tubular necrosis (intrinsic renal failure).

Urine Output

Although clinical situations vary greatly, the usual, minimal acceptable urine output for an adult is 0.5–1.0

mL/kg/h (daily volume normally 750–2000 mL/d).

Urine Protein Electrophoresis

See Protein Electrophoresis, Serum and Urine and Figure 4–4.

McGraw Hill

Copyright © McGraw-Hill Global Education Holdings, LLC.

All rights reserved.

Your IP address is 200.3.149.179

Silverchair

Urine sediment as seen with a microscope. (Reproduced, with permission, from: Greene MG [ed]: The Harriet

Lane Handbook: A Manual for Pediatric House Officers, 12th ed., Year Book Medical Publishers, Chicago,

IL, 1991.)