Pathology 1:00Pmdr. Morgan

03/08/01Nehal S./Sonia P.

Pathology 1:00pmDr. Morgan

Urinalysis

*Note: All bolded sections in the notes are test worthy! They are also bolded in the scribe.

I. Specimen Evaluation

1. Criteria for Acceptance

a. Double sterile container

b. Labeling: important for identification

1. full name

2. date of collection

3. time of collection: must be correctly preserved and properly refrigerated

4. who collected it? Important to know if there are questions about results

c. Transport time and conditions (temperature and location of specimen collection)

2. Specimen types: Where did the specimen come from?

a. Clean catch midstream-midstream to wash contaminants from urethra in the beginning, collect middle urine flow, minor abnormalities may be found but not clinically significant. For ex: squamous epithelial cell which can come from the perineum of the female. However, epithelial cells from a catheter specimen suggest pathology: squamous metaplasia of urothelial cells of the bladder.

b. Catheter: drainage bag sample not so good

3. Physical appearance

1. Color

1. yellow-due to normal pigments

i. should be normally pale

ii. very pale=high fluid intake or caffeine/beer intake (low specific gravity)

iii. pale urine due to diuresis in diabetes but high specific gravity from sugar

iv. radiographic contrast media (high specific gravity)

v. dark-low fluid intake (yellow pigments more concentrated)

2. red

i. beets (some persons may lack enzymes that break them down)

ii. hematuria (RBCs)-clinically significant

iii hemoglobunuria-hemolyzing of hemoglobin which is excreted in urine

iv. methemoglobinuria (iron oxidized to ferric state in hemoglobin

1) seen in individuals with NADH cytochrome b5 reductase deficiency

2) hemoglobinopathy-hemoglobin M

v. myoglobinuria due to seizures, skeletal muscle damage, chronic alcoholics

vi.Phenolphtalein (alkaline)

vii some Porphyrias

3. yellow/brown to green/brown

i. bilirubinuria

4. orange/red to orange/brown

i. phenazopyridines (urinary analgesics)

5. dark brown to black

i. alcaptonuria: very rare metabolic disease with homogentisic acid in urine

ii. levadopa

iii.melanin in urine

6. blue/green

i. chlorophyll (mouth deodorants)

2. Clarity

1. clear-normal

2. cloudy

i. bacteria or yeast

ii. chyluria-lymphatic fluid in the urine

iii crystaluria-crystals in the urine

iv. lipiduria: nephrotic syndrome, fat embolism

v. mucous

vi. pyuria-pus in the urine, UTI with a lot of WBCs

vii.spermatozoa

3. Specific Gravity

1. measurement of urine concentrations of dissolved solutes: high specific gravity=high concentration of solutes that are dissolved, low value=dilute urine

2. measured by:

a. refractometer: look at the refractive index compared to those of standard salt solutions; GOLD STANDARD in measuring specific gravity

b. urinometer: looks like a fishing float; elongated and made out of glass with numbers on the side. Basically, put it in urine, it will sink depending on how much the specific gravity. Then, take the reading of the urinometer.

c. dipstick: urinalysis strips; there is a specific gravity block on the dipstick. Has absolutely no correlation with the specific gravity measured by the refractometer.

4. Chemical Analysis

-dipsticks-reagent strips for urinalysis. Basically, a plastic strip with rectangles on them. These different rectangles contain compounds that will react with substances in urine. Then, look at a chart and read off the concentrations of the different substances in the urine. Now, there are automated machines that will read the strip.

A. pH

1. Normal=4.6-8

2. Acidic urine

i. high meat/protein diet due to uric acid

ii cranberries-acidifies urine, preventing the growth of bacteria

iii drugs and other substances (look in notes)

3. alkaline urine

i. vegetarian diet (due to presence of oxalate)

ii sodium bicarb, potassium citrate, etc.

iii drugs used to treat urinary calculi-stones occurring in the kidneys, ureter, or bladder

iv bacterial overgrowth

B. Protein

1. Normally, you should not see very much protein in the urine. Maybe Tamm-Horsfall protein, lubricant for the urinary tract

2. This is very important: reagent strips are sensitive to albumin, but not sensitive to immunoglobulins. EX. pt with multiple myeloma, a malignant disorder of plasma cells, will be producing abnormal immunoglobulins. They will accumulate in high concentrations and be flushed through the urine. Reagent strip will not detect this

3. False positives and false negatives can occur with these dipsticks.

4. Always confirm dipstick proteinuria with another method-sulfasalicylic acid

5. If proteinuria exists, then characterize it by urine protein electrophoresis and immunofixation. Types of proteinuria:

i. glomerular-albumin and other proteins usually retained in the plasma, caused by an intrinsic renal disorder

ii tubular-small proteins usually filtered by glomerulus, like B-2 microglobulin, are usually reabsorbed by tubules. If only small proteins detected in urine, something is wrong with the renal tubules.

iii. overflow- too much of a particular protein in the plasma so it will spill over into the urine. Ex: hemoglobin, myoglobin, or immunoglobulins

iv. VERY IMPORTANT: Bence-Jones protein- free immunoglobulin light chains. Diagnostic of a malignancy(multiple myeloma or a lymphoma). These light chains are very nephrotoxic and can cause renal damage. Remember, these are not detected by urinalysis reagent strips.

C. Glucose

a. False-negative result:

i. Remember this: Ascorbic acid (Vitamin C)-can delay diagnosis of diabetes

ii. antibiotics

iii low pH

iv. high ketones (eg. Diabetic ketoacidosis)

v. sugars other than glucose will not give a positive result on the reagent strip for glucose. Only specific for glucose. Test infants for other reducing substances, other sugars, with a Copper reduction test. If glucose test is neg. and copper reductions test is pos., consider metabolic diseases

b. False-positive result:

i. bleach or other cleaning agents

D. Ketones-important to detect in diabetes and chronic alcoholics. Most chronic alcoholics are in starvation. They are getting most of their calories form the alcohol=protein calorie malnutrition.

a. reagent strips more sensitive to acetoacetic acid than acetone; not reactive to beta-hydroxybutyrate. All of these are ketones, but depending on the stage of DKA, not all the ketones will be detected.

b. If reagent strip is pos. for ketones, do a confirmatory test.

E. Blood: not really measuring blood , but measuring hemoglobin. Red blood cells have to lyse to see a positive dipstick result.

a. correlate a positive dipstick result with a microscopic exam. Are the RBCs in the urine? Myoglobin for example can give a positive blood test but negative exam for RBCs. Basically, correlate a positive blood test with the presence or absence of RBCs and hemosiderin. Hemosiderin is a breakdown product of hemoglobin and present in urine in cases of intravascular hemolysis.

b. false-negative result

i. Vitamin C

c. false-positive result

i. myoglobin

F. Bilirubin: it is initially unconjugated when it is broken down from red blood cells. In the liver, it becomes conjugated making bilirubin water-soluble and excretable.

a. conjugated bilirubin is increased with biliary tract obstruction or injury to hepatocytes. Urine urobilinogen will be negative with hepatic obstruction, because it is formed by colonic bacteria.

b. When bilirubin is detected with a dipstick, then do a confirmatory test, an ictotest

c. false-negative result

i. ascorbic acid

d. false-positive result with some drugs

G. Urobilinogen

a. increased with causes of conjugated hyperbilirubinemea; urine bilirubin may be negative with jaundice due to hemolytic anemia (predominantly unconjugated)

H. Nitrate-important in the diagnosis of UTIs

a. increased when bacteria that reduce urinary nitrate to nitrite are present in significant numbers; most enteric gram neg. organisms.

b. in detection of UTI's, the sensitivity is 65%, specificity is 90%. This means with a positive nitrate, we can say with 90% positivity that organisms are present that will reduce nitrate to nitrite. However, some of these organisms may just be on the perineum, a contaminant. So, it may not be a UTI.

c. Correlate with leukocyte esterase, a microscopic exam, and a urine culture. With a true UTI, tend to grow one microorganism, maybe two. Colony count is greater than 100,000. With contaminated overgrowth, on a culture, tend to get a whole bunch of different microorganisms not present in very high concentration.

d. False-negative result:

i. non-nitrite forming organisms: enterococci, staphylococci, yeast

ii vitamin C

e. False positive result:

i. bacterial contamination and overgrowth

*Don’t diagnose a UTI based only on a positive nitrite.

I. Leukocyte esterase

a. enzymatic marker for the presence of neutrophilic granulocytes. Neutrophils are the biggest responder to bacterial infection in the urinary tract or any other sort of bacterial infection. So in a real UTI, should have both pos. nitrite and leukocyte esterase tests.

b. In detection of UTI, sensitivity 92%, specificity 90%.

c. Reasons for a UTI with neg. leukocyte esterase: non-bacterial infection, neutropenia

d. false-positive results: form contamination by vaginal or perineal fluids

J. Ascorbic acid: give false-negatives in test for glucose, blood, bilirubin, and nitrite

II. Microscopic Examination: if dipstick findings are completely negative, chances of having microscopic findings are zero.

a. Specimen preparation

1. Centrifuge urine to concentrate sediment to look at formed and cellular elements.

2. Examine unstained specimen under phase contrast or polarized light.