Introduction to RENAL FUNCTION TEST
FORMATION OF URINE
- Nephron is the functional unit of kidney.
- Strucure of nephron-bowman’s capsules,proximal convoluted tubule(PCT),loop of Henle , distal convoluted tubule, collecting tubule.
- Process involves 2 steps-
- a)Glomerular filtration
- b)tubular reabsorption
RENAL THRESHOLD SUBSTANCES
- Certain substances in blood whose excretion in urine is dependent on their concentration.Such substances are called renal threshold substances.
- Defined as its concentration in blood beyond which it is excreted into urine.
- Renal threshold for glucose-180mg/dl
- For calcium-10mg/dl
- For ketone bodies-3mg/dl
- For bicarbonate-30mg/dl
TEST TO ASSESS RENAL FUNCTION
- Glomerular function test
- Tubular function test
- Analysis of blood/serum
- Urine examination
- The rate at which creatinine and urea are removed or cleared from the blood into the urine is termed clearance.
- Defined as that volume of plasma from which a measured amount of substance can be completely eliminated into urine per unit of time expressed in millilitres per minute.
- Ideal substance for measurement of clearance.
- Endogenous metabolic product synthesized at a constant rate for a given individual & cleared essentially only by glomerular filtration.
- Levels are higher in males than females.
- Analysis is simple & inexpensive using colorimetric assays.
- Value is derived by mathematically relating the serum creatinine concentration to the urine creatinine concentration excreted during a period of time usually 24 hours.
- Specimen collection include both a 24hr urine specimen & a serum creatinine value ,ideally collected at midpoint of 24hr urine collection.
- Creatinine clearance is widely used to approximate GFR.
- The total volume of urine is carefully measured & the creatinine clearance is calculated by the following formula-
- Cr=creatinine clearance
- Ucr=urine creatinine clearance
- Vur=urine volume excreted in 24 hr
- Pcr=serum creatinine concentration
- 1.73/A=normalization factor for body surface area
- Reference range-
- Males-97ml/min per 1.73m sq. to 137 ml/min per 1.73m sq.
- Females-88ml/min per 1.73 m sq. to 128ml/min per 1.73 m sq.s
UREA CLEARANCE TEST
- Urea clearance is not as sensitive as creatinine clearance because urea is partially reabsorbed by renal tubules.
- Hence its clearance is less than GFR.
- It is defined as volume of plasma that would be completely cleared of urea per minute.
- DIAGNOSTIC IMPORTANCE
Blood urea level is found to increase only when clearance falls below 50% normal.
- Inulin is homopolysaccharide made up of fructose.
- Neither reabsorbed nor secreted by renal tubules.
- Clearance is equal to GFR.
- Urine concentration test
- Dilution test
- PSP excretion test
- PAH(Para Amino Hippurate) clearance test
- Acidification test
URINE CONCENTRATION TEST
- This is a test to assess the renal tubular function.
- It involves the accurate measurement of specific gravity.
Other blood tests
- Serum calcium and phosphate estimation.
- Serum uric acid.
- Serum electrolytes.
- Serum urea.
- Ketone bodies
- Bile salts
- Blood pigment
- Solid masses made of crystals.
- Originate in kidneys but can be found at any point in urinary tract.
- 1.Calcium stones
- 2.Uric acid
SIGN & SYMPTOMS
- Cause severe pain
- May not occur until stone begins to move down the ureters.
- Severe pain is called renal colic.
- Pain may be located on one side of back or abdomen.
- Pain of renal colic comes &goes but is quite intense.
- Blood in urine ,vomiting,nausea,chills,fever.
- Requires complete health history assessment & a physical examination.
- Blood test for calcium,phosphorous,uric acid& electrolytes.
- Blood urea nitrogen(BUN) & creatinine to assess kidney functioning
- Examination of passed stones to determine types.
- Drinking 6-8 glasses of water a day increases urine flow.
- Dehydrated patients or with severe nausea ,vomiting may need intravenous fluid.
- Medication –narcotics ,antibiotics,allopurinol for uric acid stones, diuretics.
- It is the illness accompanying kidney failure in particular the nitrogenous waste products associated with failure of this organ.
- In kidney failure, urea & other waste products, which are normally excreted into the urine, are retained in the blood.
SIGN & SYMPTONS
- Neural & muscular-
- -fatigue, peripheral neuropathy
- -seizures, anorexia, nausea,
- -weakness, cramps.
- Endocrine & metabolic-
- -amenorrhea , sexual dysfunction, reduced body temperature
- -altered levels of amino acid
Besides renal failure it can also increased by-
- Increased production of urea in the liver due to-
- -high protein diet
- -increased protein breakdown
- -gastrointestinal bleeding
- b) decreased elimination of urea due to-
- -decreased blood flow through kidney
- -urinary outflow obstruction
- c) dehydration
- d) chronic infection of the kidney such as chronic pyelonephritis
- A detailed & accurate history & physical will help to determine if uremia is acute or chronic.
- BLOOD TEST-
- Basic metabolic panel,serum calcium & phospherous to evaluate GFR ,blood urea nitrogen & creatinine.
- Serum pot.,phosphorous, calcium , & sodium levels.
- URINE TEST-
- A 24hr urine collection for determination of creatinine clearance may be done.
- Urinalysis with microscopic examination for the presence of protein,casts,blood & pH.
- Glomerule are structures in kidneys made up of tiny blood vessels.
- These help filter blood & remove excess blood.
- Conditions that damage the glomeruli are referred to as glomerulonephritis.
- Can be both acute and chronic glomerulonephritis.
- SYMPTOMS OF ACUTE GN
- -Puffiness in face (edema)
- -urinating less often, blood in urine
- -high blood pressure
- Urinalysis test is done
- Blood & protein in urine during urinalysis are imp. markers for the disease.
- Creatinine clearance
- Total protein in urine
- Urine concentration
- Urine specific gravity
- Blood tests may show anemia, abnormal albumin levels, abnormal blood urea nitrogen, high creatinine levels
- Biopsy of the kidneys to confirm diagnosis
- CT scan ,kidney ultrasound chest x-ray
- Serum urea
- Serum creatinine
- Calcium and phosphorus estimation
- Uric acid
- Serum electrolytes
Other Biochemistry Notes
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