Renal function

Renal function tests

Renal function tests 1- General urine analysis 2- Clearance


General urine examination Fresh sample -physical -chemical -macroscopic examination -microscopical examinaton

Appearance color , turbidity PH Specific gravity Glucose Protein urea Urine sediments

Physical Characteristics of Urine Color and transparency Clear, pale to deep yellow Concentrated urine has a deeper yellow color Drugs, vitamin supplements, and diet can change the color of urine Cloudy urine may indicate infection of the urinary tract Appearance - clear turbidity colour

Physical characteristics of urine Odor Fresh urine is slightly aromatic Standing urine develops an ammonia odor Some drugs and vegetables (asparagus) alter the usual odor.


Chemical characteristics of urinepH Slightly acidic (pH 6) with a range of 4.5 to 8.0Diet can alter pHUrine PH - normally acidic Normal 4.5 -8Acidic 4.5 – 5.5Alkaline 6.5 – 8PH more than 8 less than 4 Physiologically impossible Specific gravityRanges from 1.001 to 1.035 Is dependent on solute concentration



Urine osmolality normal average 400 – 500mosm/kgMaximum 1200mosm/kgTo asses the ability of kidney to dilute or concentrate urine – tubular function

Microscopic examination sediments RBC WBC Crystals

Urine Volume Normal volume - 1 to 2 L/day Polyuria > 2L/day Oliguria < 500 mL/day Anuria - 0 to 100 mL

Renal Clearance

Renal clearance: The ability of kidneys to clear plasma from different product. or ( It is the volume of plasma that is completely cleared of the substance by the kidneys per unit time). Renal clearance provides: *a useful way of quantifying the excretory function of the kidneys * can be used to quantify the rate at which blood flows through the kidneys *as well as the basic functions of the kidneys ( glomerular filtration, tubular reabsorption ,and tubular secretion ).


If the plasma passing through the kidneys contains 1 mg of a substance in each ml and if 1 mg of this substance is also excreted into the urine each minute, then 1 ml/min of the plasma is “cleared” of the substance. Clearance rate (Cs): Cs X Ps = Us X V ( Cs is the clearance rate of a substance s, Ps is the plasma concentration of the substance, Us is the urine concentration of that substance, and V is the urine flow rate). Us X V Cs = ---------------------- P s


GFR estimation: 1-Inulin clearance can be used to estimate GFR 2-Creatinine clearance 3-plasma creatinine can be used to estimate GFR Creatinine is a by-product of muscle metabolism and is cleared from the body fluids almost entirely by glomerular filtration. - clearance of creatinine can be used to assess GFR ,but because a small amount of it is secreted by the tubules, so that the amount of creatinine excreted slightly exceeds the amount filtered so its not a perfect marker.



Its not be practical to collect urine for 24hrs in a patient for measuring creatinine clearance (CCr), so measurement of plasma creatinine concentration is measured which is inversely proportional to GFR. If GFR suddenly decreases by 50%, only half of creatinine will filtered and excreted and the other half of creatinine remains in plasma lead to increase in plasma creatinine concentration.


Estimation of Renal Plasma Flow (RPF( If a substance is completely cleared from the plasma (by secretion), the clearance rate of that substance is equal to the total RPF. (RPF X Ps) would be equal to the amount excreted in the urine (Us X V). Thus, (RPF) could be calculated as: Us XV RPF= ------------------- = Cs Ps


Because the GFR is only about 20 % of the total plasma flow, a substance that is completely cleared from the plasma must be excreted by tubular secretion as well as glomerular filtration.


PAH: about 90 % of PAH cleared from the plasma. Therefore, the clearance of PAH can be used as an approximation of RPF. Renal plasma flow is 650 ml/min


Filtration Fraction Calculation (FF) FF: is the fraction of plasma that filters through the glomerular membrane. FF = GFR/RPF = 125/650 = 0.19 Renal plasma flow (PAH clearance) 650 ml/min and the GFR (inulin clearance) 125 ml/min


Comparisons of Inulin Clearance with Clearances of Different Solutes Substance Clearance Rate (ml/min) Glucose 0 Sodium 0.9 Chloride 1.3 Potassium 12.0 Phosphate 25.0 Inulin 125.0 Creatinine 140.0


Kidney Diseases In acute renal failure, ability of kidneys to excrete wastes & regulate blood volume, pH, & electrolytes is impaired Rise in blood creatinine & decrease in renal plasma clearance of creatinine Can result from atherosclerosis, inflammation of tubules, kidney ischemia, or overuse of NSAIDs



Kidney Diseases (continued) Glomerulonephritis is inflammation of glomeruli Autoimmune attack against glomerular capillary basement membranes Causes leakage of protein into urine resulting in decreased colloid osmotic pressure & resulting edema


Kidney Diseases continued In renal insufficiency, nephrons have been destroyed as a result of a disease Clinical manifestations include salt & H20 retention & uremia (high plasma urea levels) Uremia is accompanied by high plasma H+ & K+ which can cause uremic coma


Treatment includes hemodialysis Patient's blood is passed through a dialysis machine which separates molecules on basis of ability to diffuse through selectively permeable membrane Urea & other wastes are removed

Hemodialysis