table of contents
- Urinalysis
- METHODS OF URINE COLLECTION
- MACROSCOPIC URINALYSIS
- Read more :Stool Analysis: A Comprehensive Guide to Digestive Health and Disease Detection The first part of a urinalysis is direct visual observation. Normal, fresh urine is pale to dark yellow or amber in color and clear. Normal urine volume is 750 to 2000ml/24hr. Turbidity or cloudiness may be caused by excessive cellular material or protein in the urine or may develop from crystallization or precipitation of salts upon standing at room temperature or in the refrigerator. Clearing of the specimen after addition of a small amount of acid indicates that precipitation of salts is the probable cause of turbidity. A red or red-brown (abnormal) color could be from a food dye, eating fresh beets, a drug, or the presence of either hemoglobin or myoglobin. If the sample contained many red blood cells, it would be cloudy as well as red.
- CHEMICAL ANALYSIS
- Read more : MICROSCOPIC URINALYSIS
- PH
- The glomerular filtrate of blood plasma is usually acidified by renal tubules and collecting ducts from a pH of 7.4 to about 6 in the final urine. However, depending on the acid-base status, urinary pH may range from as low as 4.5 to as high as 8.0. The change to the acid side of 7.4 is accomplished in the distal convoluted tubule and the collecting duct.
- Specific Gravity (sp gr)
- Specific gravity (which is directly proportional to urine osmolality which measures solute concentration) measures urine density, or the ability of the kidney to concentrate or dilute the urine over that of plasma. Dipsticks are available that also measure specific gravity in approximations. Most laboratories measure specific gravity with a refractometer. Specific gravity between 1.002 and 1.035 on a random sample should be considered normal if kidney function is normal. Since the sp gr of the glomerular filtrate in Bowman's space ranges from 1.007 to 1.010, any measurement below this range indicates hydration and any measurement above it indicates relative dehydration. If sp gr is not > 1.022 after a 12 hour period without food or water, renal concentrating ability is impaired and the patient either has generalized renal impairment or nephrogenic diabetes insipid us. In end-stage renal disease, sp gr tends to become 1.007 to 1.010. Any urine having a specific gravity over 1.035 is either contaminated, contains very high levels of glucose, or the patient may have recently received high density radiopaque dyes intravenously for radiographic studies or low molecular weight dextrin solutions. Subtract 0.004 for every 1% glucose to determine non-glucose solute concentration. Read more :Urinalysis: A Key Diagnostic Tool for Detecting Health Issues and Maintaining Well-being Protein Dipstick screening for protein is done on whole urine, but semi-quantitative tests for urine protein should be performed on the supernatant of centrifuged urine since the cells suspended in normal urine can produce a falsely high estimation of protein. Normally, only small plasma proteins filtered at the glomerulus are reabsorbed by the renal tubule. However, a small amount of filtered plasma proteins and protein secreted by the nephron (Tamm-Horsfall protein) can be found in normal urine. Normal total protein excretion does not usually exceed 150 mg/24 hours or 10 mg/100 ml in any single specimen. More than 150 mg/day is defined as proteinuria. Proteinuria > 3.5 gm/24 hours is severe and known as nephrotic syndrome. Dipsticks detect protein by production of color with an indicator dye, Bromphenol blue, which is most sensitive to albumin but detects globulins and Bence-Jones protein poorly. Precipitation by heat is a better semiquantitative method, but overall, it is not a highly sensitive test. The sulfosalicylic acid test is a more sensitive precipitation test. It can detect albumin, globulins, and Bence-Jones protein at low concentrations. In rough terms, trace positive results (which represent a slightly hazy appearance inurine ) are equivalent to 10 mg/100 ml or about 150 mg/24 hours (the upper limit of normal). 1+ corresponds to about 200-500 mg/24 hours, a 2+ to 0.5-1.5 gm/24 hours, a 3+ to 2-5 gm/24 hours, and a 4+ represents 7 gm/24 hours or greater.
- Glucose
- Less than 0.1% of glucose normally filtered by the glomerulus appears in urine (< 130 mg/24 hr). Glycosuria (excess sugar in urine) generally means diabetes mellitus. Dipsticks employing the glucose oxidase reaction for screening are specific for glucos glucose but can miss other reducing sugars such as galactose and fructose. For this reason, most newborn and infant urines are routinely screened for reducing sugars by methods other than glucose oxidase (such as the Clinitest, a modified Benedict's copper reduction test).
- Read more :The Importance of Urinalysis in Detecting Diabetes and Kidney Diseases Ketones
- Ketones (acetone, aceotacetic acid, beta-hydroxybutyric acid) resulting from either diabetic ketosis or some other form of calorie deprivation (starvation), are easily detected using either dipsticks or test tablets containing sodium nitroprusside.
- Nitrite
- A positive nitrite test indicates that bacteria may be present in significant numbers in urine . Gram negative rods such as E. coli are more likely to give a positive test.
- Leukocyte Esterase A positive leukocyte esterase test results from the presence of white blood cells either as whole cells or as lysed cells. Pyuria can be detected even if the urine sample contains damaged or lysed WBC's. A negative leukocyte esterase test means that an infection is unlikely and that, without additional evidence of urinary tract infection, microscopic exam and/or urine culture need not be done to rule out significant bacteriuria.
Urinalysis
METHODS OF URINE COLLECTION
1. Random collection taken at any time of day with no precautions regarding contamination. The sample may be dilute, isotonic, or hypertonic and may contain white cells, bacteria, and squamous epithelium as contaminants. In females, the specimen may cont contain vaginal contaminants such as trichomonads, yeast, and during menses, red cells.2. Early morning collection of the sample before ingestion of any fluid. This is usually hypertonic and reflects the ability of the kidney to concentrate urine during dehydration which occurs overnight. If all fluid ingestion has been avoided since 6 p.m. the previous day, the specific gravity usually exceeds 1.022 in healthy individuals.
3. Clean-catch, midstream urine specimen collected after cleansing the external urethral meatus. A cotton sponge soaked with benzalkonium hydrochloride is useful and non-irritating for this purpose. A midstream urine is one in which the first half of the bladder urine is discarded and the collection vessel is introduced into the urinary stream to catch the last half. The first half of the stream serves to flush contaminating cells and microbes from the outer urethra prior to collection. This sounds easy, but it isn't (try it yourself before criticizing the patient).
Urinalysis can reveal diseases that have gone unnoticed because they do not produce striking signs or symptoms. Examples include diabetes mellitus, various forms of glomerulonephritis, and chronic urinary tract infections.
The most cost-effective device used to screen urine is a paper or plastic dipstick. This microchemistry system has been available for many years and allows qualitative and semi-quantitative analysis within one minute by simple but careful observation. The color change occurring on each segment of the strip is compared to a color chart to obtain results. However, a careless doctor, nurse, or assistant is entirely capable of misreading or misinterpreting the results. Microscopic urinalysis requires only a relatively inexpensive light microscope.
MACROSCOPIC URINALYSIS
The first part of a urinalysis is direct visual observation. Normal, fresh urine is
pale to dark yellow or amber in color and clear. Normal urine volume is 750 to
2000ml/24hr.
Turbidity or cloudiness may be caused by excessive cellular material or
protein in the urine or may develop from crystallization or precipitation of
salts upon standing at room temperature or in the refrigerator. Clearing of the
specimen after addition of a small amount of acid indicates that precipitation
of salts is the probable cause of turbidity.
A red or red-brown (abnormal) color could be from a food dye, eating fresh
beets, a drug, or the presence of either hemoglobin or myoglobin. If the sample
contained many red blood cells, it would be cloudy as well as red.
CHEMICAL ANALYSIS
PH
The glomerular filtrate of blood plasma is usually acidified by renal
tubules and collecting ducts from a pH of 7.4 to about 6 in the final urine.
However, depending on the acid-base status, urinary pH may range from as low as
4.5 to as high as 8.0. The change to the acid side of 7.4 is accomplished in
the distal convoluted tubule and the collecting duct.
Specific Gravity (sp gr)
Specific gravity (which is directly proportional to urine osmolality which
measures solute concentration) measures urine density, or the ability of the
kidney to concentrate or dilute the urine over that of plasma. Dipsticks are
available that also measure specific gravity in approximations. Most
laboratories measure specific gravity with a refractometer.
Specific gravity between 1.002 and 1.035 on a random sample should be
considered normal if kidney function is normal. Since the sp gr of the
glomerular filtrate in Bowman's space ranges from 1.007 to 1.010, any
measurement below this range indicates hydration and any measurement above it
indicates relative dehydration.
If sp gr is not > 1.022 after a 12 hour period without food or water,
renal concentrating ability is impaired and the patient either has generalized
renal impairment or nephrogenic diabetes insipid us. In end-stage renal
disease, sp gr tends to become 1.007 to 1.010.
Any urine having a specific gravity over 1.035 is either contaminated,
contains very high levels of glucose, or the patient may have recently received
high density radiopaque dyes intravenously for radiographic studies or low
molecular weight dextrin solutions. Subtract 0.004 for every 1% glucose to
determine non-glucose solute concentration.
Protein
Dipstick screening for protein is done on whole urine, but semi-quantitative
tests for urine protein should be performed on the supernatant of centrifuged
urine since the cells suspended in normal urine can produce a falsely high
estimation of protein. Normally, only small plasma proteins filtered at the
glomerulus are reabsorbed by the renal tubule. However, a small amount of
filtered plasma proteins and protein secreted by the nephron (Tamm-Horsfall
protein) can be found in normal urine. Normal total protein excretion does not
usually exceed 150 mg/24 hours or 10 mg/100 ml in any single specimen. More
than 150 mg/day is defined as proteinuria. Proteinuria > 3.5 gm/24 hours is
severe and known as nephrotic syndrome.
Dipsticks detect protein by production of color with an indicator dye,
Bromphenol blue, which is most sensitive to albumin but detects globulins and
Bence-Jones protein poorly. Precipitation by heat is a better semiquantitative
method, but overall, it is not a highly sensitive test. The sulfosalicylic acid
test is a more sensitive precipitation test. It can detect albumin, globulins,
and Bence-Jones protein at low concentrations.
In rough terms, trace positive results (which represent a slightly hazy
appearance inurine ) are equivalent to 10 mg/100 ml or about 150 mg/24 hours
(the upper limit of normal). 1+ corresponds to about 200-500 mg/24 hours, a 2+
to 0.5-1.5 gm/24 hours, a 3+ to 2-5 gm/24 hours, and a 4+ represents 7 gm/24
hours or greater.
Glucose
Less than 0.1% of glucose normally filtered by the glomerulus appears
in urine (< 130 mg/24 hr). Glycosuria
(excess sugar in urine) generally means diabetes mellitus. Dipsticks employing
the glucose oxidase reaction for screening are specific for glucos glucose but
can miss other reducing sugars such as galactose and fructose. For this reason,
most newborn and infant urines are routinely screened for reducing sugars by
methods other than glucose oxidase (such as the Clinitest, a modified
Benedict's copper reduction test).
Ketones
Ketones (acetone, aceotacetic acid, beta-hydroxybutyric acid) resulting from
either diabetic ketosis or some other form of calorie deprivation (starvation),
are easily detected using either dipsticks or test tablets containing sodium
nitroprusside.
Nitrite
A positive nitrite test indicates that bacteria may be present in
significant numbers in urine . Gram negative rods such as E. coli are more
likely to give a positive test.
Leukocyte Esterase
A positive leukocyte esterase test results from the presence of white blood cells either as whole cells or as lysed cells. Pyuria can be detected even if the urine sample contains damaged or lysed WBC's. A negative leukocyte esterase test means that an infection is unlikely and that, without additional evidence of urinary tract infection, microscopic exam and/or urine culture need not be done to rule out significant bacteriuria.