Urinalysis Flashcards
Objectives
1
Q
Describe a “clean catch” technique for evaluating urine and the importance of patient education
A
- void small amount into toilet, then collect some urine in container
- Why do you void first?
- To get rid of the squamous cells and microbes from outer urethra aka to avoid bacteria
- Was it midstream? Look for squamous cells
- **Always instruct the pt on how to collect the urine **
- Why do you void first?
2
Q
Catheter-obtained specimen
A
- Catheterization of the bladder through the urethra for urine collection is done only in special circumstances, i.e., in a comatose or confused adult patient, or in an infant or child unable to cooperate with obtaining a clean catch specimen
3
Q
Performing a complete urinalysis
A
- First do the visual exam, then the dipstick exam, and then spin the urine and look at the sediment under the microscope.
- Remember not to discard the urine immediately – may need to send for culture!
- Urine should be examined promptly (within 30-60 minutes) or otherwise refrigerated
- Microscopic urinalysis at initial evaluation and on an ongoing basis can reveal vital information about the health of the kidney. Evaluation should be performed by centrifugation of at least 12 mL of a freshly voided specimen.
4
Q
Visual Exam- Color
A
- Color
- normal fresh urine is pale to dark yellow in color due to urobilinogen and urobilin (metabolic products of hemoglobin breakdown)
- Intensity of yellow color generally indicates the concentration of the urine- usually most concentrated in first AM void
- A pink, red, orange, or brown color is abnormal and could be from:
- The presence of RBCS (hematuria): pinkish / red
- The presence of free hemoglobin (hemoglobinuria) or free myoglobin (myoglobinuria): reddish / reddish brown
- Presence of bilirubin: brownish – classically “cola-colored”
- Some drugs / foods can affect urine color: (i.e. pyridium and rifampin cause an orange discoloration; excessive beets cause a red discoloration)
- Pyridium = Phenazopyridine = AZO Standard, a bladder analgesic available OTC that folks use when they have a UTI to help with the dysuria
***the pt’s history, as well has the subsequent dipstick and micro will help you make the determination of what is causing the color abnormality
5
Q
Visual Exam- Clarity
A
- Normal urine is clear
- Turbidity or cloudiness may be caused by excessive cellular material (pyuria or hematuria), excessive crystals, or excessive protein in the urine (proteinuria)
- Pyuria = too many WBCs in the urine
- Hematuria = too many RBCs in the urine
- Again, the dipstick and micro will help give you the answer as to what is causing the turbidity
6
Q
Urine Smell
A
- Normal urine smell is “Urinoid”
- A more disagreeable, malodorous smell is sometimes noted with UTIs
- The glucosuria of diabetes mellitus can cause a sweet, fruity odor
- Some foods, most notably asparagus, will also cause a urine odor change
7
Q
Urine Dipstick
A
- A paper or plastic dipstick composed of sections with different test reagents embedded into the fibers
- The reagents react with components of the urine; color changes on each segment of the strip are then compared with a chart (there are also some automated urine dipstick analyzers)
- After the visual exam – noting the color, clarity, and odor of the urine - then do the urine dipstick
- Dipstick is also known as “urine reagent strip”
- Reagent: a substance used in a chemical reaction to detect, measure, examine, or produce other substances
8
Q
Dipstick Testing
A
- The proper way to use a dipstick is to fully immerse it in urine for 2-3 seconds, turn it horizontally on a paper towel to absorb runoff and keep chemicals from running onto the adjacent patch, and wait at least 30 seconds before reading.
- Don’t hold it vertically!
- Some reagents can be read in 30 seconds, others must wait up to two minutes to note change…
- Don’t forget to put the lid back on the container of dipsticks as exposure to light and air can affect accuracy of dipsticks
9
Q
Dipstick- standard items checked
A
- Specific Gravity
- pH
- Blood (aka Heme)
- Protein
- Glucose
- Ketones
- Nitrate
- Leukocyte Esterase
- Bilirubin
10
Q
Specific Gravity (sp gr)
A
- Specific gravity is the relative weight of a specific volume of liquid compared with an equal volume of distilled water.
- Sp gr of pure water is 1.00
- Urine sp gr is directly proportional to urine solute concentration; i.e. sp gr is a reflection of how concentrated or dilute the urine is…
- Specific gravity <1.008 is dilute and >1.020 is concentrated
- As long as the pt’s kidneys are functioning well, think of sp gr as a clue to the pt’s hydration status
- high sp gr = concentrated urine =dehydrated
- low sp gr = dilute urine = well hydrated
- Sp gr typically ranges between 1.002 and 1.035
- Sp gr is generally > 1.020 after a 12 hour period without food or water (so in the morning after a long sleep)
11
Q
Dipstick: pH
A
- The glomerular filtrate of blood plasma is usually acidified by renal tubules and collecting ducts from a pH of 7.4 (normal arterial blood pH) to slightly acidic (i.e. 5.5 – 6.5) in the final urine
- Recall that lactic acid, uric acid, other organic acids from metabolic processes are excreted into the urine to maintain the body’s acid/base balance, i.e. the kidneys are responsible for eliminating the daily nonvolatile metabolic acid load
- Diminished renal acid excretion — A regular Western diet (lots of protein) generates a daily nonvolatile metabolic acid load of approximately 50 to 100 mEq/day that must be excreted by the kidneys. Acid-base balance is maintained by excreting these hydrogen ions in the urine
- Due to variables,, urinary pH may range from as low as 4.5 to as high as 8.0.
- One point to note is that an alkaline urine in a patient with a UTI suggests the presence of a urea-splitting organism, i.e. a bacteria that produces urease
- Examples are Proteus, Klebsiella, or Pseudomonas species
12
Q
Urease
A
- activity tends to increase the pH of its environment. Ureases are found in numerous bacteria, fungi, and algae.
- Urease is a high molecular weight cytoplasmic enzyme that hydrolyzes urea to ammonia and carbon dioxide. Ammonia combines with hydrogen to form ammonium; the ensuing reduction in free hydrogen ion concentration leads to alkalinization with the urine pH being well above 7.0 and sometimes as high as 9.0. Alkaline urine sometimes has an ammoniacal smell.
- A urease producing bacteria that we will talk more about in the GI module is helicobacter pylori. (H.pylori create “an island of alkalinitiy in a sea of acidity” – lowing surrounding pH to survive in the low pH of stomach acids…)
- Struvite stones are composed of magnesium ammonium phosphate (aka struvite) and calcium carbonate-apatite. Normal urine is undersaturated with ammonium phosphate, and struvite stone formation occurs only when ammonia production is increased and the urine pH is elevated, which decreases the solubility of phosphate. The only situation in which this occurs in humans is with an upper urinary tract infection with a urease-producing organism, such as Proteus or Klebsiella. Urease breaks down urinary urea into ammonia plus carbon dioxide:
- Urea → 2NH3 + CO2
- The ammonia produced by this reaction then combines with water:
- NH3 + H2O → NH4+ + OH-
- The net result is increased availability of ammonium in an alkaline urine
13
Q
Dipstick: Blood
A
- The dipstick test for blood detects the peroxidase activity of the hemoglobin in erythrocytes
- A positive blood on dipstick usually reflects the presence of RBCs in the urine – even just a few extra RBCs in urine (not grossly visible)
- Less common reasons to have a positive heme result on dipstick are the presence of free hemoglobin (from severe hemolytic anemia) or free myoglobin (from rhabdomyolysis) in the urine. In these cases, the microscopic evaluation would NOT show the expected RBCs generally seen with the most common cause of a positive dipstick for blood – RBCs in the urine!
- Bottom line, confirm positive blood/heme on dipstick by looking for RBCs in micro exam!
14
Q
Dipstick testing for hematuria
A
- is at best a screening tool which needs the support of microscopy to make a definitive diagnosis
- Make sure you know if a reproductive-aged woman is on her period or not before pursuing a work-up of hematuria!
15
Q
Rhabdomyolysis
A
- is a potentially life-threatening syndrome resulting from the breakdown of skeletal muscle fibers with leakage of muscle contents into the circulation. Rhabdomyolysis literally means striated muscle dissolution or disintegration
- Clinical features are often nonspecific, and tea-colored urine is usually the first clue to the presence of rhabdomyolysis. Screening may be performed with a urine dipstick in combination with urine microscopy. A positive urine myoglobin test provides supportive evidence.
- With muscle injury, large quantities of potassium, phosphate, myoglobin, creatine kinase (CK) and urate leak into the circulation. Under physiologic circumstances, the plasma concentration of myoglobin is very low (0 to 0.003 mg per dL). If more than 100 g of skeletal muscle is damaged, serum haptoglobin binding capacity becomes saturated.6 The circulating myoglobin becomes “free” and is filtered by the kidneys.
- Myoglobin in the renal glomerular filtrate can precipitate and cause renal tubular obstruction, leading to renal damage.
16
Q
Hemolytic anemia
A
- is a form of anemia due to hemolysis, the abnormal breakdown of red blood cells (RBCs), either in the blood vessels (intravascular hemolysis) or elsewhere in the human body (extravascular, but usually in the spleen). Large amounts of “free” hemoglobin are then seen in the urine….
17
Q
The dipstick test for blood
A
- detects the peroxidase activity of the hemoglobin in erythrocytes. However, myoglobin and free hemoglobin will also catalyze this reaction, so a positive test may indicate hematuria, myoglobinuria, or hemoglobinuria.
- False positive readings are most often due to contamination with menstrual blood. Generally, try not to get your urinalysis on female pts done during their menstrual cycles…
18
Q
Dipstick: Protein
A
- In general, only a small amount of filtered plasma proteins and protein secreted by the nephron tubules (“Tamm-Horsfall” protein) can be found in normal urine.
- Abnormal amounts of protein in the urine is termed proteinuria
- The dipstick reagent is most sensitive to the presence of albumin, which is typically the major protein “spilled”
- The glomerular capillary wall is permeable only to substances with a molecular weight of less than 20,000 daltons..once filtered, low molectular weight proteins are mostly reabsorbed by the proximal tubule cells. A very small amount of protein (known as Tamm-Horsfall protein) is actually secreted by the tubular cells and is normally found in the urine.
19
Q
Dipstick: protein results
A
- Trace or 1+ corresponds to about 300-500 mg/24hrs
- 2+ more protein in urine
- 3+ even more protein in urine
-
4+ even more protein in the urine…
- The dipstick provides a rough estimate of degree of proteinuria; pts with persistent postitive urine dipsticks should do 24 hour urine collection to more precisely quantify degree of protein loss….
- Trace to 1+ proteinuria can be defined as transient / functional (e.g. due to fever,, exercise-induced, UTI) or persistent (present on at least two out of three specimens and not in the setting of a known cause of transient proteinuria) increased.
- The results are graded as negative (less than 10 mg per dL), trace (10 to 20 mg per dL), 1+ (30 mg per dL), 2+ (100 mg per dL), 3+ (300 mg per dL) or 4+ (1,000 mg per dL). This method preferentially detects albumin and is less sensitive to globulins or parts of globulins (heavy or light chains or Bence Jones proteins).
20
Q
Immunoglobulins and Bence-Jones proteins
A
- One fairly important limitation to the standard dipstick for protein is its relative selectivity for albumin
- Dipsticks detect globulins and Bence-Jones* protein poorly
- If suspected, this type of protein may be picked up by testing the urine with a sulfosalicylic acid protein precipitation test**
- *Immunoglobulins and Bence-Jones proteins (monoclonal immunoglobulin light chains ) are spilled in the urine in some disease states – the most important and common being Multiple Myeloma (a hematologic malignancy of immunoglobulin-producing cells, i.e. plasma cells)
- Detection of non-albumin proteinuria — The dipstick is insensitive to non-albumin proteins, most notably nephrotoxic immunoglobulin light chains in the setting of multiple myeloma. A screen for the presence of such proteins may be performed with the sulfosalicylic acid test.
- Sulfosalicylic acid (SSA) detects all proteins in urine and may be useful in patients with acute kidney injury (AKI) of unclear etiology and a urine dipstick that is negative for protein. A positive SSA test in conjunction with a negative dipstick usually indicates the presence of non-albumin proteins in the urine, most often immunoglobulin light chains.
21
Q
albumin dipstick
A
- Persistent albumin excretion of 30-300 mg/day is termed moderately increased albuminuria (formerly termed “microalbuminuria”)
- Persistent albumin excretion > 300 mg/day (the level at which a standard dipstick generally becomes positive) is termed severely increased albuminuria (formerly termed “macroproteinuria”)
- Recall that Increased urinary protein excretion may be the earliest manifestation CKD….However, when assessing protein excretion, the urine dipstick is a relatively insensitive marker for initial increases in protein excretion, not becoming positive until protein excretion exceeds 300 to 500 mg/day …so, you need to order the spot urine albumin to creatinine ratio
22
Q
Nephrotic Syndrome
A
- Proteinuria > 3.5 gm/24 hours known as “Nephrotic range” proteinuria and represents a profound disorder of glomerular selective filtration
- In addition to nephrotic range Proteinuria, the syndrome consists of hypoAlbuminemia, hyperLipidemia, and generalized Edema (PALE mnemonic)
- Common causes of nephrotic syndrome:
- minimal change disease
- diabetic nephropathy
- focal segmental glomerulosclerosis
- On a dipstick 4+ protein usually represents nephrotic range proteinuria
- Nephrotic syndrome is more common in children, where the MC cause is “Minimal change disease” also known as lipoid nephrosis
- Also see increased risk of thrombosis and increased risk of infections in nephrotic syndrome….
29
Q
Normal Dipstick
A
37
Q
Glomerular vs Non-glomerular
A
