Part 2: Renal Physiology and Renal Function Tests Flashcards by Geno Alinsub

Q

Glomerular Filtration Rate

Measures the rate at which kidneys can remove or clear a filterable substance from the blood

A

Clearance Test

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Q

Glomerular Filtration Rate

→ Removal of a substance from plasma into urine over a fixed period

→ Not bound to proteins

→Filtered, neither reabsorbed nor secreted

A

Clearance Test

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Q

Glomerular Filtration Rate:Clearance Test

In clearance test, if the marker is something that is reabsorbed, what would happen to the volume?

A

the current volume over the fixed period of time would not be measured

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Q

Glomerular Filtration Rate: Clearance Test

In clearance test, if the marker is something that is secreted, what would happen to the volume?

A

amount would not be fixed (would increase)

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Q

Glomerular Filtration Rate: Clearance Test

Unit?

A

milliliters/minute

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Q

Glomerular Filtration Rate: Clearance Test

Markers?

A

Exogenous and Endogenous substance

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Q

Glomerular Filtration Rate: Clearance Test

A high GFR in clearance test means there is?

A

Efficient excretion

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Q

Glomerular Filtration Rate: Clearance Test

A low GFR in clearance test means there is?

A

Inefficient excretion

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Q

Glomerular Filtration Rate: Clearance Test

What is the formula for clearance test?

A

U X V / P

→ U = urine concentration of the marker
→ P = plasma concentration of the marker
→ V = total urine volume (24-hr sample)
→A = patient’s body surface area

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Q

Formula for Clearance Test

What is the average bodu surface area (A)

A

1.73 m2

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Q

Shows the body surface area of an individual

A

Nomogram

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Q

If you see this card review the image of the nomogram

A

Go na

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Q

Marker

→ Substances that are not naturally produced in the body

→ Needs to be administered

A

Exogenous

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Q

Type of Marker: Exogenous

What are the markers under exogenous

A

Inulin
Radioactive markers

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Q

Type of Marker: Exogenous

→ Reference method
→ Not routinely done
→ Soluble, freely, filtered, neither secreted nor reabsorbed

A

Inulin

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Q

Type of Marker: Exogenous

Inulin value for male?

A

Male: 127mL/min/1.73m2

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Q

Type of Marker: Exogenous

Inulin value for female?

A

118 ml/min/1.73m2

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Q

Type of Marker: Exogenous

What are the example of radioactive markers?

A

125I-iothalamate
99m Tc-DTPA
Iohexol
51Cr-EDTA

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Q

Marker

Naturally produced in the body

A

Endogenous

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Q

Marker: Endogenous

A common type of marker under endogenous

A

Creatinine Clearance (Ccrea)

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Q

Marker: Endogenous

Waste product of muscle metabolism that is produced enzymatically by creatine phosphokinase from creatine

A

Creatinine

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Q

Marker: Endogenous

What enzyme produces creatinine and where?

A

Creatinine phosphokinase from creatine

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Q

Marker: Endogenous

Normal values of Creatinine Clearance for female?

A

75 - 112 ml/min

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Q

Marker: Endogenous

Normal values of Creatinine Clearance for male?

A

85 - 125 ml/min

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# T or F Males have lower value in creatinine clearance since they have less muscle mass

F (opposite; males have higher value since they have more muscle mass)

Familiarize the disadvantages of creatinine clearance

1. Some creatinine is secreted by the tubules 2. Chromogens in plasma react in the chemical analysis 3. Medications inhibit tubular secretion 4. Bacteria break down urinary creatinine 5. A diet heavy in meat can raise creatinine 6. Not a reliable indicator in patients suffering from muscle-wasting diseases 7. Depends on the completeness of a 24-hour collection 8. It must be corrected for BSA (unless normal)

# T or F

# Glomerular Filtration Tests Greatest source of error in any clearance procedure using urine

Improperly timed urine specimens

# Glomerular Filtration Tests What are the methods that do not require the collection of timed (24-hour) urine specimens

1. Estimated glomerular filtration rate eGFR using serum creatinine 2. Cystatin C 3. Beta2-microglobulin

What are the 3 methods in Calculated Glomerular Filtration Estimate?

1. Cockcroft & Gault 2. Modification of Diet in Renal Disease (MDRD) 3. Chronic Kidney Disease Epidemiology Collaboration CKD-EPI (2021)

# 3 methods in Calculated Glomerular Filtration Estimate Variables: Age, Sex, Weight (Kg)

Cockcroft & Gault

# 3 methods in Calculated Glomerular Filtration Estimate Formula for Cockcroft & Gault

(140 - age) (wt in kg) / 72 x Serum crea in mg/dl) | x 0.85 if female

# 3 methods in Calculated Glomerular Filtration Estimate **6 Variables (previous):** Age, Sex, Serum urea nitrogen, Serum creatinine, Race, and Serum albumin **Simplified MDRD based on four variables:** Serum creatinine, Age, Race, and Sex

Modification of Diet in Renal Disease (MDRD)

# 3 methods in Calculated Glomerular Filtration Estimate Formula for Modification of Diet in Renal Disease (MDRD)

GFR = 173 X Serum creatinine^1.154 x Age^-0.203 x 0.742 (if patient is female) x 1.212 (if patient is black)

# 3 methods in Calculated Glomerular Filtration Estimate → Recommended formula by the National Kidney Disease Education Program (NKDEP) → Serum creatinine obtained with an enzymatic IDMS-traceable assay → Correspond more closely to the isotope dilution mass spectrophotometry (IDMS) → More accurate and precise when telling the status of the patient’s kidney

MDRD-IDMS-traceable formula

# 3 methods in Calculated Glomerular Filtration Estimate MDRD-IDMS-traceable formula

GFR = 175 X Serum creatinine^-1.154 x Age^-0.203 x 0.742 (if patient is female) x 1.212 (if patient is black)

# 3 methods in Calculated Glomerular Filtration Estimate → Estimates GFR from serum creatinine, age, sex → Formerly race was included

Chronic Kidney Disease Epidemiology Collaboration CKD-EPI (2021)

# 3 methods in Calculated Glomerular Filtration Estimate Familiarize the formula for Chronic Kidney Disease Epidemiology Collaboration CKD-EPI (2021)

please look at the ppt or trans tinatamad ako itype

# 3 methods in Calculated Glomerular Filtration Estimate Normal Reference Range: Stage 1 GFR =

Stage 1 GFR = greater than 90 mL/min/1.73

# Calculated Glomerular Filtration Estimate Normal Reference Range: Stage 2 GFR =

Stage 2 GFR = 60-89 mL/min/1.73 m

# Calculated Glomerular Filtration Estimate Normal Reference Range: Stage 3 =

Stage 3 = 45-59 mL/min/1.73

# Calculated Glomerular Filtration Estimate Normal Reference Range: Stage 4 =

Stage 4 = 15-29 mL/min/1.73

# Calculated Glomerular Filtration Estimate Normal Reference Range: Stage 5 =

Stage 5 = less than 15 mL/min/1.73 (end-stage renal disease

# Endogenous → Major end product of protein and amino acid metabolism → Freely filtered by the glomeruli but variably reabsorbed by the tubules →Can also be marker, but is not ideal because it is reabsorbed

Urea Clearance (urea)

# Endogenous: Urea Clearance What is the percentage of urea reabsorbed?

40%

# Endogenous → For screening and monitoring GFR → Small protein (MW 13,359) → Produced at a constant rate by all nucleated cells → Readily filtered by the glomerulus → Reabsorbed and broken down by the Renal Tubular Epithelial cells ( RTEs) → Not secreted by the tubules → Serum conc. can be directly related to the GFR

Cystatin C

# Endogenous → Molecular weight 11,800 → Dissociates from human leukocyte antigens at a constant rate → Rapidly removed from the plasma by GF → Enzyme immunoassay

Beta2-Microglobulin

# T or F Increase beta2- microglobulin means increased GFR

F (increased beta2- microglobulin = decreased GFR)

# Endogenous Molecular Weight of Cystatin C?

13,359

# Endogenous Molecular Weight of Beta2-Microglobulin?

11,800

# T or F GFR depends on the number of functioning nephrons and the functional capacity of these nephrons

T

Familiarize the Clinical Significance of GFR

1. Determines the extent of nephron damage 2. Monitors the effectiveness of treatment 3. Determines the feasibility of administering medications

What are the 2 methods under Tubular Reabsorption Tests?

1. Specific Gravity 2. Osmolality

# Tubular Reabsorption methods What are the tests under Specific gravity method?

1. Fishberg test 2. Mosenthal Test

# Tubular Reabsorption methods → cannot provide us with actual concentrating ability of tubules

Specific Gravity

# Tubular Reabsorption methods best measurement to know renal concentration ability

Osmometry

# 2 Tests under Specifiic Gravity patients are deprived of fluids for 24 hrs prior to measuring the specific gravity

Fishberg Test

# 2 Tests under Specifiic Gravity compares the volume and specific gravity of day and night samples

Mosenthal Test

# Tubular Reabsorption methods Measures number of particles in a solution (quantifying numbers in solution)

Osmolality

# Tubular Reabsorption methods: Osmolality Serum osmolality?

275 to 300 mOsm

# Tubular Reabsorption methods: → Renal concentration is concerned with small particles → Large MW molecules do not contribute to the evaluation of renal concentration → Preferred than SG

Osmolality

# T or F Specific gravity is more on the **number and density of the solution** than the quantity of particles | Tubular reabsorption tests

T

What are the Instruments for Measurement Osmolality?

1. Freezing point Osmometers 2. Vapor Pressure Osmometers

# Instruments for Measurement Osmolality → Measurement of freezing point depression → The freezing point depression is **directly proportional** to the amount of solute present in the solution (molality) → **Unit: **mOsm/kg

Freezing point Osmometers

# Instruments for Measurement Osmolality: Freezing point osmometers -T o F Freezing point of depression is **directly proportional** to amount of solute present in solution

T

# Instruments for Measurement Osmolality: Freezing point osmometers Familiarize the Process of Freezing point Osmometer

1. Specimen undergoes **supercooling**, once it reaches freezing initiation (point where machine is set) 2. After it reaches supercooled condition, it is subjected to crystallization through **pulse vibration** 3. Point where it crystallizes, **releases Heat of Fusion** 4. Point where there is Heat of Fusion **increases the temperature** 5. If there is a plateau, it is now called the **Freezing point of the solution**

# Instruments for Measurement Osmolality: Freezing point osmometers Try to state the process of Freezing point osmometers

Supercooling → Crystallization through Pulse Vibration → releasing of Heat of Fusion → Increase of Temperature → Plateau (Freezing point)

# Instruments for Measurement Osmolality: Freezing point osmometers A temperature sensitive probe (detecting probe in container)

Thermistore

# Instruments for Measurement Osmolality: Freezing point osmometers Temperature for freezing initiation for other specimen?

27 c

# Instruments for Measurement Osmolality → Vapor pressure depression →The **depression of dew point temperature** by solute parallels the **decrease in vapor pressure** → Magnitude of the vapor pressure decrease is **directly proportional** to the molar concentration of solute

Vapor Pressure Osmometers

# Instruments for Measurement Osmolality: Vapor Pressure Osmometers Familiarize the process of Vapor Pressure osmometers

1. After putting specimen on tray, there will be **increase in temperature** and specimen will **evaporate** 2. Once certain temperature is reached, the temperature will be **decreased/cooled**, for it to undergo **condensation** 3. As the temperature decreases, at some point, temperature reaches plateau state called **Vapor pressure or Deer point of solution**

# Instruments for Measurement Osmolality: Vapor Pressure Osmometers Try to state the process of Vapor pressure osmometers

Evaporation --> Condensation --> PLateau (vapor pressure/deer point)

# T or F Reference values for urine osmolality are difficult to establish because factors, such as fluid intake and exercise, can greatly influence the urine concentration.

T

Reference value range for urine osmolality?

50 to 1400 mOs m

What must be done by patients with Neurogenic Diabetes Insipidus and Nephrogenic Diabetes Insipidus?

Deprive patient of water for 12 hrs

# T or F Patients withNeurogenic Diabetes Insipidus and Nephrogenic Diabetes Insipidus, should be deproved of water for 24 hours

F (12 hours)

# Neurogenic Diabetes Insipidus vs. Nephrogenic Diabetes Insipidus Normal value of urine osmolality?

800 mOsm or higher (3:1 ratio)

# Neurogenic Diabetes Insipidus vs. Nephrogenic Diabetes Insipidus Process to do if urine osmolality is less than 800 mOsm?

1. Restrict fluid for another 2 hours 2. Collect urine and serum for osmolality testing 3. Patient is injected with ADH 4. Collect abnormal serum and urine in 2 and 4 hours

# Neurogenic Diabetes Insipidus vs. Nephrogenic Diabetes Insipidus If urine osmolality is less than 800 mOsm, for how long should the patient be restricted from fluid?

2 hours

# Neurogenic Diabetes Insipidus vs. Nephrogenic Diabetes Insipidus If patient has Neurogenic Diabetes Insipidus and is injected with ADH, what happens with urine osmolality?

Urine osmolality will be corrected

# Neurogenic Diabetes Insipidus vs. Nephrogenic Diabetes Insipidus If patient has Nephrogenic Diabetes Insipidus and is injected with ADH, what happens with urine osmolality?

Urine osmolality is still low

# Neurogenic Diabetes Insipidus vs. Nephrogenic Diabetes Insipidus - T o F A patient with Neurogenic DI after injection of ADH, means their kidney responds to ADH, and that they only lack Antidiuretic hormone

T

# Neurogenic Diabetes Insipidus vs. Nephrogenic Diabetes Insipidus - T o F A patient with Nephrogenic DI after injection of ADH, means their kidney is unable to respond to ADH, and that the liver have problems with the receptor

F (the **kidneys** have receptor problems; kaya nga nephrogenic) | nephrogenic = nephron

→Amount of solute-free water excreted per day → To determine ability of the kidneys to respond to the state of body hydration

Free water clearance

# T or F Free clearance water is the **Volume of creatinine** that is **cleared of solute-free water per unit time**

F (is the **Volume of blood plasma** that is **cleared of solute-free water per unit time**) | ganong kadaming water you excrete without solute

# Free Water Clearance Pre-requisite clearance to determine first before free-water clearance?

Osmolar clearance

# Free Water Clearance indicates how much water must be cleared each minute to produce a urine with the same osmolarity as the plasma

Osmolar clearance ## Footnote ganong kadaming water ang kailangan ma-clear every minute, na same ang osmolality as plasma

If u see this card, go ahead and memorize the formula of free water clearance

DO IT NA PLSSS : <<<

# Free Water Clearance - T o F Negative result in free water clearance = less amount of urine excreted & urine is less concentrated

F (Negative result in free water clearance = less amount of urine excreted and urine is **more concentrated**)

# Free Water Clearance - T o F Negative result in free water clearance = excess amount of urine excreted & urine is diluted thorugh excretion of solute-free water

F (Positive)

# Free Water Clearance - T o F A free water clearance of zero (0) means the kidney is producing **urine isosmotic** with respect to the plasma (same osmolarity)

T

What are the 3 Tubular Secretion and Renal Blood Flow Tests?

1. P-aminohippuric clearance test (PAH Test) 2. Titratable Acidity and Urinary Ammonia 3. Phenolsulfonphthalein (PSP) test

# Tubular Secretion and Renal Blood Flow Tests → Nontoxic substance → Loosely bound to plasma proteins → Permits its complete removal as the blood passes through the peritubular capillaries

P-aminohippuric clearance test (PAH Test)

# Tubular Secretion and Renal Blood Flow Tests Formula for P-aminohippuric clearance test (PAH Test)?

Cpah (mL/min) = U (mg/dl PAH) x V (mL/min urine) / P (mg/dl PAH) | pakicheck nlng sa trans or ppt if magulo

# Tubular Secretion and Renal Blood Flow Tests → Approximately a person excretes 70 mEq/day of acid in the form of titratable acid (H+), hydrogen phosphate ions (H2PO4–), or ammonium ions (NH4+).

Titratable Acidity and Urinary Ammonia

# Tubular Secretion and Renal Blood Flow Tests HOw many mEq/day of acid in the form of titratable acid (H+), **hydrogen phosphate ions (H2PO4–), or ammonium ions (NH4+),** is excreted?

70 mEq/day of acid

# Tubular Secretion and Renal Blood Flow Tests → dye-excretion test; not done since dye is administered in the patient (invasive)

Phenolsulfonphthalein (PSP) test

# Tubular Secretion and Renal Blood Flow Tests Reasons why Phenolsulfonphthalein (PSP) test is not currently perfomed?

1. Interference by medications 2. Elevated waste products in patients’ serum 3. Necessity to obtain several very accurately timed urine specimens 4. Possibility of producing anaphylactic shock