Urine - Diagnostic Studies
Urine Analysis
o pH
o Specific gravity
o Protein
o Sugar
o Microscopic examination
o Ketone bodies
pH of Urine
o The glomerular filtrate of blood is acidified by the kidneys
o From a pH of approximately 7.4 to a pH of about 6 in the urine. (7 neutral, below7 acidic, above 7 alkaline)
o Depending on the person's acid-base status, the pH of urine may range from 4.5 to 8.
o The kidneys maintain normal acid-base balance primarily through the reabsorption of sodium and the tubular secretion of hydrogen and ammonium ions.
A highly acidic urine pH occurs in:
o Acidosis
o Uncontrolled diabetes
o Diarrhea
o Starvation and dehydration
o Respiratory diseases in which carbon dioxide retention occurs and acidosis develops
A highly alkaline urine occurs in:
o Urinary tract obstruction
o Pyloric obstruction
o Salicylate intoxication
o Renal tubular acidosis
o Chronic renal failure
o Respiratory diseases that involve hyperventilation (blowing off carbon dioxide and the development of alkalosis)
Specific Gravity
o Normal specific gravity range in urine
o 1.020 -1.030 g/ml (usuall called 1020, 1030)
o The range of the specific gravity tested
o 1.005 - 1.030 g/ml
o The results of specific gravity levels in urine shows the concentrating and diluting ability of the kidneys.
o Reduced specific gravity
- diabetes insipidus
- excess fluid intake
- diabetes mellitus
o Raised specific gravity
- dehydration
- adrenal insufficiency
- nephrosis
- congestive cardiac-failure
- liver disease
o Constant specific gravity
- chronic renal disorder
Protein in urine
Normal protein range in urine
o 0 - 10 mg/dl - everything over 10 mg must be further investigated
Measuring range
o 0 - > 2000 mg/dl
Protein levels in urine
o abnormal value - greater than 10 mg/dl
o Abnormal protein values may be indicative of Proteinuria
may be benign or pathological
o Benign proteinuria
- postural
- excessive exercise
- high or low temperature
- during pregnancy
o Pathological proteinuria
- ureteric colic
- liver cirrhosis
- plasmacytoma
- cardiac insufficiency
- pyelonephritis
- glomerulonephritis
Ketone bodies
o Ketone bodies are :
beta-hydroxybutyric acid,
acetoacetic acid
acetone
They are the end-product of rapid or excessive fatty acid breakdown
o Ketones are present in the urine when the blood levels of ketones surpass a certain threshold. Fatty acid release from adipose tissue is stimulated by hormones: glucagon, epinephrine, and growth hormone.
o The levels of these hormones are increased in starvation (whether related to excess alcohol use or not), uncontrolled diabetes mellitus, and a number of other conditions.
Urine Sugar
o Diabetes
o Gestational diabetes
o Cushing's syndrome
o Genetic
o Fanconi's syndrome
o Chronic renal failure
o Pregnancy
o Lead toxicity
Microalbuminuria
o Microalbuminuria - the measurement of small amounts of albumin in the urine that cannot be detected by urine dipstick methods.
o excretion of 30-300mg of albumin/24 h
o or 20-200 µg/min or 30-300 µg/min of creatinine on two of three urine collections
o an indicator of subclinical cardiovascular disease
o marker of vascular endothelial dysfunction
o an important prognostic marker for kidney disease
o in diabetes mellitus
o in hypertension
o increasing microalbuminuria level during the first 48 hours after admission to an intensive care unit predicts elevated risk for acute respiratory failure , multiple organ failure , and overall mortality
RBCs in the urine
WBCs
contaminants such as : -
squamous cells
cotton fibres
starch granules
The RBC cast of glomerular pathology:
The WBC cast of pyelonephritis:
The nonspecific granular, waxy and hyaline casts:
Broad casts as a sign of the markedly decreased output of chronic renal failure. They are usually quite wide and are upto 2-6 times as wide as the above nonspecific casts (thus the name "broad"):
The pathologic crystals of metabolic diseases and poisonings can be seen as well:
CYSTINE:
Tyrosine
Calcium Oxalate
Finally one might find the "coffin-lid" struvite crystals associated with urea-splitting bacteria
In patients with nephrotic syndrome one might be able to find fat casts
Uric acid crystals
Certain investigations related to micturition
o Micturating Cystourethrogram (MCUG)
Indications for imaging
Vesicoureteric reflux in children - in recurrent UTI
Stress incontinence
Urethral stricture
Bladder dysfunctions
Contra Indications for imaging
Current - urinary tract infection
Contrast media allergies
o Dipsticks impregnated with chemicals which change colour
o . Creatinine - product of creatine metabolism by the muscle. Is filtered by the kidney, but not absorbed in the renal tubule.
o Formula for creatinine clearance: C=UV P
C = clearance rate
U = urine concentration
V = urine volume
P = plasma concentration
Normal creatinine clearance is 115-125 ml/min (corrected for body surface area) Usually 24 hour collection of urine is done; blood drawn when urine collection is completed.
What are the substances reabsorbed in the renal tubule?
o Reabsorption: water, sodium, and other substances leave the lumen of the tubule and enter the blood.
o Secretion: substances from the blood enter lumen of the tubule.
o Glucose and amino acids - completely reabsorbed
o Filtered water - 99% reabsorbed
o Urea - about 50% reabsorbed
o Creatinine - none reabsorbed
o Electrolytes - determined by need
o Renin - released by special cells located near the glomerulus (juxtaglomerular cells) in response to:
o Reduction in GFR
o Sympathetic stimulation - Combines with angiontensinogen, a plasma protein that circulates in the blood to form angiotensin I, then converted to angiotensin II (potent vasoconstrictor and stimulator of aldosterone release).
o Erythropoietin - released in response to hypoxia. Acts on bone marrow to stimulate production and release of RBCs. Persons with chronic hypoxia often have increased RBCs (polycythemia) due to increased erythropoietin levels. Examples: congestive heart failure, chronic lung disease, living at high altitude.
o Vitamin D - activated and converted in kidney. Affects calcium metabolism.
o . Urinalysis - Normal urine contains metabolic wastes and little, if any, plasma proteins, blood cells, or glucose.
o Casts are moulds of distal nephron lumen. Tamm and Horsfall mucoprotein (gel-like substance) forms the matrix of casts.
Hyaline casts - contain Tamm and Horsfall mucoprotein, without cells. Develop when protein content of urine is high such as nephrotic syndrome
Urinary Tract Infection
o Midstream urine collected
o after cleansing the meatus
o bacterial count Normal : 10000 or less / ml organisms
o Infection : 100000 or more / ml organisms
Electromyography
o Studies detecting the electrical activity of the detrusor muscle
Voiding cystourethrogram revealing bilateral grade 3 reflux into small, scarred kidneys.
Renal papillary necrosis
o Coronal image of the left kidney from a CT Urogram shows numerous irregular collections of contrast arising
from the calyces, some streak-like densities and overall distortion of the normal medullary-calyceal anatomy
Ureteropelvic jn obstruction
