Urinalysis Flashcards
What is inulin?
Inulins are a group of naturally occurring polysaccharides produced by many types of plants. Inulin is uniquely treated by nephrons in that it is completely filtered at the glomerulus but neither secreted nor reabsorbed by the tubules. This property of inulin allows the clearance of inulin to be used clinically as a highly accurate measure of glomerular filtration rate(GFR).
It is given through IV infusion and is examined with timed urine tests to calculate GFR. It is very accurate but expensive.
Why is using creatinine practical for determining GFR?
It is not bound to plasma proteins so it is filtered freely, it is not reabsorbed by renal tubules, it’s fairly constant with relation to muscle mass, and only a small amount is secreted by renal tubules (10%). Since it is secreted, GFR tends to slightly overestimate renal function.
When doing UA, specimens must be tested within ____ hours of specimen collection. If they won’t be in lab within this time frame, they must be _____.
2 hours, refrigerated.
Urine always has some bacteria in there so it will grow if it’s just sitting around at room temperature. This will cause false results.
True or False: 24 hour specimens are unacceptable for UA testing
True
True or False: Midstream clean catch is used for culture
True.
Wash external genitalia with soap and rinse.
Catch midstream specimen in a sterile urine container.
If a patient is on ______ , let the lab know so they can process with longer incubation if necessary.
Antibiotic therapy
Why use 24 hour UA?
Reference ranges are all based on 24 hours.
What are the 3 categories for urine volume? what are the volume cutoffs per 24 hours? What do these tell you about the disease process?
Polyuria - increased urine volume (greater than 2000 mL/24h) can be caused by defective hormonal regulation of volume homeostasis (ADH), defective renal salt/water absorption, or osmotic diuresis (DM).
Oliguria - decreased urine volume (less than 500 mL/24h) can be caused by prerenal, postrenal, or renal parenchymal disease.
Anuria - very decreased urine volume (less than 100 mL/24h)
What are possible colors of urine and what do they mean? (4)
- Yellow-green-brown
- bile pigments (mostly bilirubin) (dark foam if shaken; concentrated urine with white foam)
- Orange-red-brown
- excreted urobilinogen (breakdown product of heme)
- Pink-red
- hematuria, hemoglobinuria, myoglobinuria, beet ingestion
- Dark brown/black
- methemoglobin, rhabdomyolysis (cola-colored)
What can the clarity/turbidity of urine tell you? What are 2 abnormal findings?
The clarity/turbidity of urine can tell you if there is undissolved solid material (especially cells or crystals) in the urine.
Chyluria - lymphatic flow obstruction e.g. filariasis
Lipiduria - fat globules in nephrotic syndrome, trauma
True or False: if urine smells weird, ask the lab… or something
True….
True or False: When doing urine dipsticks, you have to make sure you’re watching the time
True.
Automated instruments save the hassle
True or False: for urine dipstick test, it’s best to test the urine as soon as possible after receipt
True
True or False: urine samples must be at room temperature before testing with dipstick
True
What does specific gravity of urine tell you about renal function?
It tells you about the kidney’s concentrating ability.
- Decreased (less than 1.001) means that the patient might have polydipsia, diuretic therapy, or diabetes insipidus
- Increased (more than 1.035) means that the patient might be dehydrated, have diabetes mellitus, proteinuria, CHF, addison’s disease, or SIADH.
- Helpful when the patient has acute oliguria. A SG higher than 1.01 suggests intact tubular function and a pre-renal source of oliguria while fixed isosthenuria, SG 1.008-1.012 suggests renal tubular dysfunction, most likely renal tubular acidosis.
Whats the range of pH for normal urine? What’s the mean?
- 6 - 8.0
- 0
What can acidic urine indicate? How about alkaline?
Acidic - metabolic or respiratory acidosis, drugs, diet high in protein, cranberries
Alkaline - renal tubular acidosis, UTIs, excess bicarbonate ingestion, respiratory or metabolic alkalosis, several foods especially citrus and with large meals (alkaline tide)
How much protein is in normal urine?
Less than 0.5 g/day in urine
How can you find out what proteins are in urine?
Urine Protein Electrophoresis
What are caveats for using dipstick method for testing protein?
- It is only sensitive to albumin
- Bence-Jones protein (in MM and macroglobulinemia) is easy to miss on dipstick, you need to use electrophoresis and immunofixation
- Markedly alkaline urine may give falsely low results because reaction is pH dependent (acidic environment)
- Microalbuminuria is also not detected by dipstick as it’s below detectable range
True or False: Dipstick only detects glucose, but no other sugars
True
What are caveats for using dipstick to detect glucose? (2)
False positive if jar is left open
False negative results in presence of excess vitamin C
What are ketones and what do they indicate if it’s in urine? What is an issue with using dipstick to detect ketones?
Ketones are a product of lipid metabolism. They are normally undetectable in urine but if it’s positive, then the patient may have diabetes, alcoholism, cirrhosis, prolonged fasting, or heavy exercise.
Dipstick only detects acetoacetic acid but not the other kind of ketones (acetone and hydroxybutyrate)
When a dipstick urine test is positive for blood, what must you further differentiate between? (4)
- hemoglobinuria
- myoglobinuria
- hematuria
- hemosiderin
What if a dipstick is positive for nitrite?
It means that there is gram negative bacteria in the urine.
A negative result doesn’t necessarily rule out.
What does positive dipstick for leukocyte esterase show? What are some caveats?
It shows that there are neutrophils in the urine (can be from inflammation or perhaps fighting off bacterial infection).
Other sources of esterases (trichomonads and eosinophils) may lead to false positive results.
Chronic inflammatory cells (e.g. lymphocytes) will not be detected. Chronic cystitis may be missed.
True or False: microscopic examination of urine sediment is best done within 2 hours of collection or refrigerate specimen up to 48 hours.
True
What are you looking for in centrifuged urine sediment?
- Cells (epithelial, RBC, WBC)
- Casts (cellular vs noncellular)
- Crystals
- Organisms/Other
“CCCO”
What does it mean when a RBC is dysmorphic/distorted in shape in the UA?
It means that hte blood is glomerular in origin because it had to squeeze past a damaged glomerulus. These often present with RBC casts too
True or False: Pyuria (WBC in urine) proves infection
False. Pyuria alone does not prove infection, only indicates inflammation
Are hyaline casts seen in normal urine?
Yes
Are waxy casts seen in normal urine?
No. Waxy casts are associated with advanced chronic renal failure.
RBC casts establish the _____ as the source of bleeding, not lower urinary tract. They signify _____ disease.
Kidney, glomerular
What does finding WBC casts in UA microscopy tell you?
Inflammation is located in the kidney
e.g. pyelonephritis, interstitial nephritis, allergic interstitial nephritis, etc
What’s this?
WBC cast. (multilobed nuclei in the cells in the cast)
What’s this? What does it indicate?
Tubular cell cast. It is different from WBC cast because the cells inside have singular round nuclei.
This finding suggests tubular damage (e.g. acute tubular necrosis, viral disease, drug/toxin exposure)
What do fatty casts indicate?
Nephrotic syndrome.
These are the oval fat bodies/maltese crosses but they get stuck in a cast.
What do granular casts indicate?
They are a non-specific finding. They are trapped cellular debris or protein aggregates. Immune complexes and fibrinogen stuck in casts can make them granular.
What is a telescoped sediment/cast?
It is a blend of various cells in a cast (e.g. RBC, WBC, fat bodies, etc). This indicates that there are a blend of issues going on.
True or False: Crystals in UA microscopy are a non-specific finding
True
