Renal Function Flashcards
Function of Kidney
Concentration of Urine
Reabsorption of Nutrients
Acid base and electrolyte balance
Excretion of waste
Blood pressure
Water reabsorption and concentration
Hormonal Regulation of Body Water
Anti-Diuretic Hormone (Vasopressin)
Regulates water reabsorption
Vasopressin Regulation
Increase ADH, increases water absorption
Decrease ADH, decreases water reabsorption
Disease state with Increase ADH
Inappropriate ADH secretion
Disease state with Decrease ADH
Diabetes insipidus
Osmolality Defintion
Concentration of solutes dissolved in a body’s water
Expressed in milliosmoles (mOsm)/kilogram of water
Osmolality Measure
Osmotic pressure across body membranes
Measure of the osmoles of solute or dissolved particles per kg
Osmometry
Term used for the analysis osmolality
Formula 1 for Osmolality
2.0(Na+) + (glucose/20) + (BUN/3)
Formula 2 for Osmolality
1.86(Na+) + (glucose/18) + (BUN/2.8) + 9
Osmolar Gap
Difference between the calculated and measures osmolalities
Urine Osmolarity 24 hr Collection
300-900 mOsm/kg
Urine Osmolarity Random
50-1200 mOsm/kg
Urine to Serum Ratio
1.0-3.0
Serum Osmolarity
275-295 mOsm/kg
Osmolar Gap
5-10 mOsm/kg
Principles of ABG Measurement
Freezing Point Decrease
Vapor Pressure Decrease
Boiling Point Increase
Osmotic Pressure Increase
Freezing Point Osmometry
Determined super-cooling the sample below the freezing point
- Initiated by physical shock or very cold stir wire
- Water-ice mixture produced which remains at freezing point plateau long enough for temperature to be measured
- Uses a 2 point calibration against salt solutions
Vapor Pressure Osmometry
Changes in concentration of solutes are accompanied by linear and proportional chances in properties
- Vapor pressure is a force exerted by the gaseous phase of a two phase system
- The pressure of the vapor that is formed above its liquid is called the vapor pressure
Common Increases to Osmolar Gap
> 10 mOsm/kg
Mannitol
Glycine
Methanol
Ethylene glycol
Higher the gap, the worse the prognosis
Basic Body Fluid Compartments
Two basic compartments
Intracellular Fluid Compartment (ICF)
Extracelluar Fluid Compartment (ECF)
Water Osmolality
Moves passively across semi-permeable membranes
Lytes and other molecules do not
Osmotic Pressure
Thirst Mechanism
Thirst Center in Hypothalamus
Osmoreceptors stimulated by increase in ionic concentration
Renal Clearance
Determined by Glomerular Filtration Rate (GFR)
The mL/minute blood filtered by the kidney
Creatinine Clearance Calculation
(U x V)/P x 1.73/A
U = Urine Creatinine
V = Volume/min
P = Plasma Creatinine
A = Area of patient - obtained via chart
Non-Protein Nitrogen Compounds
NPN
Nitrogen containing compounds that are not proteins
BUN, Uric Acid, Creatinine/Creatine, Ammonia
Renal Disease Marker
Creatinine
Muscular Disorders Marker
Creatine
Jaffe Reaction
Picric Acid reacts with NaOH
Reaction creates Alkaline-Picrate Creatinine Complex
Yellow-Orange Color inidicator
BUN
Blood Urea Nitrogen
Urea
Urine compound of Nitrogen
Secretion of Ammonia to remove excess Nitrogen
Azotemia
Increase levels of BUN in plasma
Uremia
Increase BUN with renal failure
BUN Increases Means
Low renal profusion
Renal Disease
High Protein Intake
Dehydration
BUN Decrease Means
Low Protein Intake
Severe Liver Disease
Severe Vomiting or Diarrhea
Enzymatic detection of BUN
Conversion of urea to ammonia by enzyme urease
BUN — urease reaction to create ammonia + CO2
Berthelot Reaction
Ammonium ion is reacted with phenol and hypochlorite in an alkaline medium to form indophenol
Nitroprusside is used to catalyze the reaction - blue color
Enzymatic Assay
Ammonia generated from urease
Urease reacts with oxo-glutarate in presence of glutamate dehydrogenase and NAD(P)H
Chemical Method
Urea is reacted directly with diacetyl to produce diazine
- Not as commonly used as enzymatic methods
BUN/Creatinine ratio in healthy individuals
10:1 to 20:1 ratio
Pre-renal azotemia ratio
Increase ratio
20:1 to 30:1
Post-renal azotemia ratio
Increase ratio of»_space;>20:1 with high creatinine level
Low BUN coniditions
Decrease ratio <10:1
Associated with low urea production as in liver disease or malnutrition
Uric Acid Product from
Purine Metabolism
Increased Uric Acid
Gout - abnormal deposition or uric acid crystals
Renal Insufficiency - not filtered
UA can also elevate in malignancies (ie myelogenous leukemia)
Decrease Uric Acid
Rare
Uric Acid Methodology
Conversion of Uric Acid to Allantoin
Uric Acid + Phosphotungstic acid = Tungsten Blue
Formation of Allantoin
Breakdown of uric acid under action of enzyme uricase
Use heparinize plasma, serum or urine
Avoid lipemia and hemolysis
Urine pH 8 to avoid precipitation
Ammonia General Info
Produced from deamination of amino acids
Bacterial metabolism in the gut
Converted to BUN in liver
Can be toxic especially to neural cells
Ammonia Clinical Application
Increase hepatic failure
Reyes Syndrome
Pediatric disorder
Post Viral Infection with Aspirin Administration
Shows fatty infiltration of liver
Inherited deficiencies of urea cycle
Ammonia Methodology
Direct measurement
Using Ion Selective Electrode
- Ammonium ion converted to ammonia dependent on pH
Enzymatic Method
- Measuring conversion of NADPH to NADP
- Glutamate dehydrogenase
