![Serum or plasma osmolality = 2[Na+] + BUN + Glucose
(measurement in mg/dl) 2.8 18
Eg: Na= 123mEq/L
Glucose= 98mg/dl
Urea nitrogen = 22mg/dl
=2(123)+ (22/2.8)+(98/18) =259.3 milli-osmoles/ kg
• Major osmotic substance in normal plasma are sodium, chloride,
glucose and urea.
• Osmolal gap is the difference between the measured osmolality
and calculated osmolality.](https://image.slidesharecdn.com/renalfunctiontest-250623073623-782345b2/85/renal-function-test-screening-tests-tubular-function-tests-GFR-47-320.jpg)
renal function test - screening tests, tubular function tests,GFR
- 1. MS.AKHILA VC DEPARTMENT OF BIOCHEMISTRY MSC MLT CLINICAL BIOCHEMISTRY LECTURER RENAL FUNCTION TESTS AND RENAL CALCULI
- 2. FUNCTIONS OF KIDNEY Excretion of waste products. Maintain water balance Excretion of sodium, potassium, hydrogen ions to maintain the pH Electrolyte balance Production of calcitriol and erythropoietin Filtration: 180 L/day of water with all sodium, chlorides, sugar amino acids
- 3. Screening for kidney diseases • Complete urine analysis • Serum urea and creatinine tests • Serum electrolytes measurement
- 4. To assess renal function 1. To assess glomerular function • GFR • Clearance testes 2.Glomerular permeability • Test for proteinuria
- 5. 2.To assess tubular functions • Reabsorption studies • Secretion tests • Concentration and dilution tests • Renal acidification
- 7. To assess glomerular functions GFR-glomerular filtration rate. It is the volume of fluid filtered from glomerular capillaries to bowman's capsule per mint Calculation • The GFR is calculated by measuring any chemical that has steady level in blood and is freely filtered but neither reabsorbed or secreted by kidney.
- 8. • GFR is typically recorded in unit of volume per time. • Normal value of GFR is 125ml / min. • It is a measure of functional capacity of kidney and indicates no. of functioning nephrons.
- 9. Glomerular function test includes • Clearance tests 1.Creatinine clearance 2.Urea clearance 3.Inulin clearance
- 10. Clearance : clearance is defined as the volume of blood or plasma completely cleared of a substance per unit time by both kidneys. It is expressed as milliliter of plasma per minute. • Clearance estimate the amount of plasma that must have passed through the glomeruli per minute with complete removal of substance to account for the substance actually appearing in the urine.
- 11. Clearance = mg of substance excreted per minute mg of substance per mL of plasma It is calculating using by the formula C =U x V p U=concentration of substance in the urine V=the ml of urine excreted per minute P=concentration of substance in plasma or serum • If the substance is freely filtered across the Capillary wall, and neither secreted nor reabsorbed, • then its clearance is equal to glomerular filtration
- 12. • A substance which meets these requirements is an ideal filtration marker. • If the substance is also secreted by the tubules, the clearance exceeds GFR. • For those which are reabsorbed by tubules, clearance is less than GFR.
- 14. Mechanism Result Example Substances filtered neither reabsorbed nor excreted GFR = clearance Inulin, Creatinine Substance filtered; reabsorbed and excreted GFR clearance ≅ Uric acid Substances filtered; partially reabsorbed Clearance < GFR Urea Substances filtered;, secreted but not reabsorbed Clearance > GFR Diodrast, PAH
- 16. •Creatinine clearance •Creatinine is waste product formed from Creatine phosphate. About 98% Creatine pool is in muscle. •About 1.6% is converted to Creatinine per day which is rapidly excreted. •Since the productions is continuous the blood level will not fluctuate much making Creatinine an ideal substance for the test.
- 17. •Creatinine excretion is constant in a particular person. Hence the urine creatinine is sometimes used to check whether the 24 hr •urine sample does actually contain total urine volume or not. •This is important when urine is collected from children and mentally retarded persons.
- 18. •In order to circumvent the difficulty of urine collection, nowadays it is customary to express urinary concentration of other substances per gram of creatinine rather than per 24 hrs urine.
- 19. • Endogenous substance • Does not require iv administration • Normal value (130 ml/minute) is slightly higher. • Accurate than urea clearance.
- 20. Procedure • Give 500 ml water to the patient to promote good urine flow. • After 30mnts ask to empty the bladder and discard the urine. • Exactly after 60minutes again void the bladder and collect the urine and note the volume. • Take one blood sample along with it.
- 21. • Creatinine level in blood and urine are tested and calculate the clearance . • Uncorrected clearance = ( U/P ) x V Where , U = concentration of the Creatinine in urine V = volume of urine formed in one minute.ml/mnt (The 24 hrs urine collection is not necessary for the Creatinine clearance test). P = concentration of the Creatinine in plasma.
- 22. • It is useful to correct the clearance value with body surface area. • This is important, especially in children, and persons with short or tall frame. • Creatinine clearance corrected for surface area could be calculated as U x V x 1.73 ––––––––––– P x A
- 23. NORMAL RANGE OF CREATININE CLEARANCE: 95-105 ml/min Interpretation of creatinine clearance • A decreased creatinine clearance is very sensitive indicator of reduced glomerular filtration rate. • Clearance value up to 75% of the average normal value may indicate adequate renal function .
- 24. • The importance of Creatinine clearance is in the early detection of functional impairment of kidney. •Changes in plasma Creatinine which may not apparently indicate abnormal function may show gross changes in the value of clearance.
- 25. •For example, suppose the plasma creatinine level is 1 mg/dl and the clearance is 100 ml/minute. A rise in plasma creatinine by another mg (=2 mg/dl) will decrease the clearance value by 50%.
- 26. Advantages 1. Extra-renal factors will rarely interfere. 2. Conversion of Creatine phosphate to Creatinine is spontaneous, non-enzymatic. 3. As the production is continuous, the blood level will not fluctuate. Blood may be collected at anytime. 4. It is not affected by diet or exercise.
- 27. Disadvantages 1. When the GFR is reduced, the secretion component is increased, and will vitiate the results. 2. When GFR is severely reduced, extra-renal excretion increases. Then the major route becomes the degradation by intestinal bacterial flora. 3. Very early stages of decrease in GFR may not be identified by creatinine clearance (creatinine blind area).
- 28. Urea Clearance Test 1. Importance of Urea Clearance The urea clearance is less than GFR, because urea is partially reabsorbed . 2. Urea clearance is the number of ml of blood which contains the urea excreted in a minute by kidneys.
- 29. Procedure • Allow the patient to have a normal breakfast. • At 9 am give a cup of water and the patient is instructed to void the bladder, and urine is discarded. • At 10 am bladder is completely emptied and the volume of urine is measured and the urine urea is estimated. • A blood sample is taken and blood urea is also estimated.
- 30. Maximum Urea Clearance The urea clearance is calculated by the formula U x V/P where U = mg of urea per ml of urine; P = mg of urea per ml of plasma V = ml of urine excreted per minute. This is called maximum urea clearance and the normal value is found to be 75 ml/minute.
- 31. Standard Urea Clearance •But the clearance value is decreased when V, the volume of urine, is less than 2 ml/minute. •Then it is called standard urea clearance, where the normal value is found to be 54 ml/minute, and is calculated •as: U x √ V P
- 32. Interpretation of Urea Clearance Value i. If the value is below 75% of the normal, it is considered to be abnormal. ii. The values fall progressively with failing renal function. • The clearance value may be abnormal even though the plasma urea values are within normal limits. The plasma urea values will start to rise only when the clearance value falls below 50% of the normal.
- 33. Inulin clearance Inulin is a Homopolysaccharide of fructose Inulin is an ideal substance to be used for determination of renal clearance because: • It is completely filtered from plasma through glomerulus. • It is neither reabsorbed nor secreted by the renal tubules. • It is not metabolized in body and It is excreted unchanged in urine
- 34. • Hence inulin clearance rate is always equal to GFR. •Inulin Clearance value is the most accurate measure of GFR. •It is not suitable for routine use , because it is an exogenous substance. •It is a foreign substance and has to be administered intravenously. •Normal value : about 125 ml/minute.
- 35. •Procedure for Determining Inulin Clearance • 100 ml of 10% solution of Inulin is given to the patient Intravenously ( IV) within 2 hr. Urine sample formed during this period is collected . • Blood sample is also collected. • Plasma is separated and analyzed for inulin concentration.
- 36. Inulin clearance is calculated using the formula Inulin clearance = UV P Where, U = concentration of the Inulin in urine V = volume of urine formed in one minute. P = concentration of the Inulin in plasma. Interpretations In normal adults, an average inulin clearance = 125ml/min. Decreased inulin clearance indicates impaired glomerular function.
- 37. TUBULAR FUNCTION TEST These tests are based on tubular reabsorption and secretion function of kidneys and include: a) Urine Concentration Test b) Urine Dilution test c)Urine acidification test
- 38. Specific gravity of urine • The simplest test of tubular function is the measurement of the specific gravity of urine. • Specific gravity depend on the concentration of solutes. In the case of proteinuria, the specific gravity is elevated.
- 39. •Normal specific gravity of urine is 1.015-1.025. •Theoretical extremes are 1.003 to 1.032. •The specific gravity will be decreased in excessive water intake, in chronic nephritis, and in diabetes insipidus. •It is increased in diabetes mellitus, in nephrosis and in excessive perspiration
- 40. •In chronic renal failure, the specific gravity of urine is fixed at 1.010. •The earliest manifestation of renal damage may be the inability to produce concentrated urine
- 41. URINOMETER • Principle: it is based on the principle of buoyancy. • Fill the measuring cylinder with 50 ml of urine. • Lower urinometer gently in to the urine and left it float freely. • Let urinometer settle; it should not touch the side or bottom of the cylinder.
- 42. • Take the reading of SG on the scale(lowest point of meniscus) at the surface of urine. • Take out the urinometer and immediately note the temperature. When solute concentration is high up thrust of solution increases and urinometer is pushed up(high SG). If solute concentration is low urinometer sinks further in to the urine(low SG).
- 44. • In moderate forms of kidney damage, the blood level of urea and creatinine may be within the normal limits. • The inability to excrete the waste products may be counter balanced by large urine output. • Thus the earliest manifestation of renal disease may be difficulty in concentrating the urine.
- 45. Measurement of Osmolality Definition : it is the measurement of osmoles of solute per kg of solvent ( osmol/kg or osm/kg). Calculation = total moles of solute osmoles) weight of solvent Osmometry : is the technique for measuring the concentration of particle in a solution.
- 46. Osmometer : it is a device for measuring osmotic strength of a solution. Osmolar concentration expressed in 2 ways 1) Osmolality expressed as mmol/kg of solvent 2) Osmolarity expressed as mmol /L of solution Osmolality is thermodynamically more precise expression because solution concentration expressed on weight basis are temperature independent while those base on volume will vary with temperature.
- 47. Serum or plasma osmolality = 2[Na+] + BUN + Glucose (measurement in mg/dl) 2.8 18 Eg: Na= 123mEq/L Glucose= 98mg/dl Urea nitrogen = 22mg/dl =2(123)+ (22/2.8)+(98/18) =259.3 milli-osmoles/ kg • Major osmotic substance in normal plasma are sodium, chloride, glucose and urea. • Osmolal gap is the difference between the measured osmolality and calculated osmolality.
- 48. •The osmolality of urine samples vary widely from (60 milliosmol/ kg to 1200 milliosmol/kg). •A random urine sample may have an osmolality around 600 mosmls/kg and it increases to 850 after 12 hours fluid restriction. • Normally the ratio varies from 3-4.5. The normal value of plasma osmolality is 285– 300 mosm/kg
- 49. •. Osmolality is measured with an osmometer based on the depression of the freezing point of the sample. Types • Freezing point depression • Membranous osmometer • Vapor pressure osmometry • Boiling point elevation
- 50. Boiling point elevation: It is not useful for clinical sample because proteins will undergo coagulation causing gross changes in sample composition. Freezing point depression: if concentration of the solute is increased it will lower its freezing point that -0.53⁰C. Components • Cooling fluid • Stirring rod • Thermistor • Galvanometer, potentiometer
- 51. • Working: specimen with inserted thermistor probe and stirring wire is lowered in to the cooling bath and sample is super cooled . • The sample is stirred gently during the cooling step. • When the galvanometer reading indicates that sufficient cooling has occurred, the stirrer is violently agitated to initiate crystallization .
- 52. • Galvanometer movement changes the direction as the heat of fusion is released. • The temperature of sample probe remains relatively constant for 2-3 minutes. • This temperature is the freezing point of solution and reading are displayed .
- 53. • The general principle of freezing point depression osmometers involves the relationship between the number of moles of dissolved solute in a solution and the change in freezing point. • 1 mole of a dissolved solute reduces the freezing point of water by approximately 1.86⁰C
- 54. • Vapour pressure osmometry: measurement related to the decrease in dew point of temperature of pure solvent caused by decreased in vapour pressure of solvent by the solute.
- 55. • Membrane osmometry : it is a device used to indirectly measure the polymer sample. One chamber contain pure solvent other contains a solution in which solute polymer with unknown m.w. • Solvent is permitted through the membrane , a change in concentration causes the solvent to diffuse the solute side. • the osmotic pressure decrease when water is diffused in to solution. The diffusion will stop when concentration is equilibrium. • The change in pressure is measured.
- 56. Normal value in urine : 24 hour sample = 300-9000 osmoles/kg Random sample= 50-1200 osmoles/kg of H2O In blood, Adult 280-295 osmol/kg New born = up to 266 osmoles/kg With deficiency of ADH (Central diabetes insipidus) or a Decreased response to ADH (Nephrogenic diabetes insipidus)will excrete urine with osmolality less than 300.
- 57. • Addison's disease • Amyloidosis • Hyponatremia • Hyperkalemia • Hypochloremia Decrease d in • Dehydration • Acute renal failure • Diabetes insipidus • Hyperchloremia • Hypokalemia • hypernatremia Increased
- 58. • Urine concentration and dilution tests are designed to evaluate the functional capacity of kidneys to concentrate and dilute urine. • The concentrating and diluting abilities of kidneys depend upon renal tubular reabsorption function (in renal medulla) and availability of antidiuretic hormone (ADH, also known as vasopressin).
- 59. • Kidneys fail to concentrate urine either due to renal tubular damage or due to ADH deficiency . • Urine concentration and dilution tests are quite sensitive tests for early detection of loss of renal tubular function . • Urine is concentrated by tubular reabsorption of water..
- 60. Concentration Test i. The patient is allowed no food or water after a meal at 6 pm. ii. The next day at 7 AM, the bladder is emptied and specimen is discarded. A second specimen is collected at 8 am and the specific gravity is measured.
- 61. • If the specific gravity is more than 1.022 (osmolality exceeds 850 milliosmol/kg), the patient has adequate renal function. • In normal persons, the SG may be as high as 1.032. • In the concentration test osmolality should exceed750mosmol/kg. • As the disease progresses the urine specific gravity is fixed at and around 1.010 (300 milliosmol/kg)). It is then called isosthenuria. • The measurement of the volume of urine excreted during the day and the night is another simple index of tubular function.
- 62. •Normally night volume is only half of the day volume. •But an increased excretion of urine at night or nocturia is an early indication of tubular dysfunction.
- 63. Dilution tests • The patient is not allowed to drink any water after midnight. Bladder is emptied at 7 AM and a water load is given. • Hourly urine samples are collected for the next 4 hours separately. Volume, specific gravity and osmolality of each sample are measured. • A normal person will excrete almost all the water load within 4 hours and the specific gravity of at least one sample should fall to 1.003 and osmolality to 50 mosmol/kg.
- 64. Acidification test •It is indicated in unexplained hyper chloremic metabolic acidosis. •Acidification defects may occur due to generalized tubular defects or due to genetically determined defects in ion pumps.
- 65. Procedure •Give ammonium chloride at a dose of 0.1 g/kg body wt. It is given as an enteric coated preparation to decrease gastric irritation and vomiting. •The ammonium chloride (NH4Cl) is dissociated into NH3 + and HCl •In the liver the NH3 + is immediately converted into urea.
- 66. •Therefore, Cl– ions are counter balanced by H+ to produce HCl, a powerful acid It is then excreted through urine so as to produce acidification. From the kidney it dissociated and H+ ion excreted through urine. •Urine is collected hourly, from 2 to 8 hours after ingestion. •The pH and acid excretion of each sample is measured. •At least one sample should have a pH of 5.3 or less and ammonia excretion should be 30–90 millimole/hour.
- 67. •After 8 hours collect a further 5ml blood to measure serum bicarbonate . • In chronic renal failure the pH may be low, due to coexisting metabolic acidosis, but the ammonia excretion is less. •In renal tubular acidosis, the pH 5.3 is not achieved. •Liver disease is a contra-indication to perform this test.
- 68. •Micro-albuminuria •It is also called minimal albuminuria or paucialbuminuria. It is identified, when small quantity of albumin (30-300 mg/day) is seen in urine. •The test is not indicated in patients with overt proteinuria (+ve dipstick). Early morning midstream sample is preferred. •Micro albuminuria is an early indication of nephropathy in patients with diabetes mellitus and hypertension.
- 69. •Hence, all patients who are known diabetics and hypertensive should be screened for microalbuminuria. It is an early indicator of onset of nephropathy. The test should be done at least once in an year. •It is expressed as albumin-creatinine ratio; normal ratio being •Males < 23 mg/gm of creatinine •Females < 32 mg/gm of creatinine
- 70. • Patient showing higher values on more than one occasion are considered to have microalbuminuria. • Confirmed by overnight urine collection and calculation of albumin excretion rate. • A value more than 20 micro gram / minutes confirms microalbuminuria. • Administration of ACE(angiotensin converting enzyme) inhibitors decreases the rate of microalbuminuria.
- 71. • Causes • Prerenal: strenuous exercise, fever, hypothermia, seizures, and venous congestion. • Renal: nephropathy, kidney diseases, • Post renal: UTI, hematuria
- 72. Urine tests • Albumin to creatinine ratio in random spot sample. • 24 hour urine collection with creatinine, allowing the simultaneous measurement of creatinine clearance. • Timed (eg: 4 hour or overnight sample) collection
- 73. Specific assays • Radioimmunoassay • ELISA • Nephalometry
- 74. Pathogenesis HYPERGLYCEMIA Structural changes metabolic changes functional changes Microalbuminuria Macroalbuminuria Cardiovascular diseases chronic kidney diseases