Intro to KIDNEY DISEASE AND RENAL LAB TESTS

Question 1

what is fxnal unit of kidney?

name 3 exchange processes in the nephron

Answer 1

● Kidneys receive blood supply from the renal arteries
○ 20% of cardiac output
● Functional unit of the kidney = nephron
○ 1 million nephrons/kidney
○ Filter the blood and produce urine
● 3 exchange processes in the nephron
○ Glomerular filtration
○ Reabsorption
○ Secretion

Question 2

MAIN FUNCTIONS OF THE KIDNEYS (3)

Answer 2

● Regulation
○ Fluid volume, osmolarity, blood pressure, electrolyte concentrations and acidity
● Excretion
○ Metabolic end products, urea, toxins and drugs
● Synthesis
○ Renin, erythropoietin, Vitamin D3

Question 3

ACUTE KIDNEY INJURY VS. CHRONIC

KIDNEY DISEASE

Answer 3

● AKI : An acute decrease in kidney function or Glomerular Filtration Rate (GFR) over a period of hours, days or even weeks and is associated with an accumulation of waste products and (usually) volume.
● CKD: A progressive loss of kidney function over a period of months or years
● Patients who experience AKI are at risk of developing CKD. Patients who have CKD are at risk of AKI

Question 4

define azotemia

Answer 4

– an accumulation in the blood of nitrogenous waste products (blood urea nitrogen [BUN] and creatinine)

Question 5

define hematuria

Answer 5

presence of blood in the urine

Question 6

define oliguria

Answer 6

reduced urine output defined as approximately 100-400ml in 24 hours

Question 7

define anuria

Answer 7

< 100ml of urine in 24 hours

Question 8

define pyuria

Answer 8

presence of white blood cells or pus in the urine specifically defined as > 10 WBCs/ml
• Reflects the presence of inflammation more so than infection

Question 9

Proteinuria

Answer 9

a persistent protein in the urine
• Reflects loss of the normal glomerular impermeability to filtration of plasma proteins
• Albuminuria

Question 10

what is criteria for ideal marker for kidney fxn assessment

Answer 10

○ Stable concentration in plasma
○ Physiologically inert
○ Freely filtered at the glomerulus
○ NOT secreted, reabsorbed, synthesized, nor metabolized in the kidney
○ Amount secreted at the glomerulus is equal to the amount excreted in the urine

● Glomerular Filtration Rate (GFR) cannot be measured directly

Question 11

what is SERUM CREATININE (50-110 UMOL/L)

Answer 11

• Metabolic by-product of muscle
• Serum concentration primarily determined by patient’s muscle mass
• Almost exclusively eliminated by glomerular filtration
• Inverse relationship between serum creatinine and kidney function

Question 12

what is serum creatinine affected by?

Answer 12

Affected by:
• Age
• Gender
• Weight
• Malnutrition
• Muscle Wasting
• Amputation/Paralysis
• Hydration
● Not a sensitive measure of kidney function
● Rate of change is variable depending on baseline function
○ Generally not immediate

Question 13

what can lead to decreased SCr

Answer 13

● Paralysis, low activity level
● Elderly
● Decreased muscle mass
● Cirrhosis

Question 14

what can lead to increased SCr?

Answer 14

● Renal causes
● Large dietary protein intake
● Vigorous exercise
● Increased muscle mass

Question 15

what other ways can you assess kidney fxn?

Answer 15

● Serum Creatinine
● Estimation of Creatinine Clearance
○ Cockcroft-Gault Equation
● Estimation of GFR (Glomerular Filtration Rate)
○ Modification of Diet in Renal Disease (MDRD)
○ CKD-EPI
○ Schwarz Equation (Children)
● Measured 24-hour creatinine clearance

Question 16

COCKCROFT-GAULT EQUATION

Answer 16

● Validation:
○ 249 patients, 96% male, age 18-92, with/without CKD
○ Stable Creatinine (fluctuation <20%), 2 x 24h measured CrCl
● Limited generalizability in many patients you’ll encounter

Question 17

CREATININE CLEARANCE
equation?

what hapens to CrCl as age or weight increases?

Answer 17

● Cockcroft-Gault
●Cockcroft-Gault formula** (Using SI units!)
CrCl (ml/min)=
[140-age] x Wt (kg)/SCr (µmol/L) x 1.2 (for males)
■↓ CrCl with ↑ age
■↑ CrCl with ↑ weight

Question 18

CREATININE CLEARANCE VS.

GLOMERULAR FILTRATION RATE

Answer 18

● Both are estimates of renal function
● CrCl
○ Surrogate marker of renal function
○ More often used to determine drug dosages
● GFR
○ Used to stage chronic kidney disease (more in upcoming lectures)
○ Reported by the lab when a serum creatinine is measured

Question 19

BLOOD UREA NITROGEN (2.9-8.2
MMOL/L)

what is it dependent on?

Answer 19

Concentration of nitrogen (as urea) in the serum
• Dependent on urea production which occurs in the liver, glomerular filtration, and tubular reabsorption
• In conjunction with other laboratory data, it can be used to monitor hydration, renal function, protein tolerance and catabolism
• Also used to predict the risk of uremic syndrome in patients with severe renal failure

Question 20

what causes elevated BUN? (4)

Answer 20

• high protein diets
• upper GI bleeding
• dehydration/volume depletion
• Acute kidney injury (and CKD)

Question 21

what causes decreased BUN? (3)

Answer 21

• typically low BUN does not have pathophysiological
consequences
• May be low in malnutrition or who have profound
liver damage
• fluid overload (dilution)

Question 22

URINALYSIS

3 things that macroscopic analysis loks at

Answer 22

General appearance:
Colour
• Varies from normally clear to dark yellow or amber, depending on the concentration of solutes

Turbidity – cloudiness or haziness • Can occur if urates or phosphates crystalize or precipitate in the urine
• Large numbers of WBC or RBC present

Foamy appearance
• Presence of protein or bile acids

Question 23

URINALYSIS

MICROSCOPIC ANALYSIS
normally how many:
microorganisms
RBC
WBC
epithelial cells
casts
crystals

Answer 23

▪ Microorganisms (zero to trace)
▪ RBC (1 to 3/HPF)
▪ WBC (0-2/HPF)
▪ Epithelial cells (0 or 1/HPF)
▪ Casts
▪ Cylindrical masses of glycoproteins that form in tubules
▪ Normal = a few clear casts
▪ Abnormal
▪ Hyaline (sometimes normal)
▪ Cellular casts (WBC, RBC, epithelial)
▪ Granular casts
▪ Crystals (normally = none)

Question 24

CHEMICAL ANALYSIS

Answer 24

Urine Dipstick
• Protein (zero to trace)
• pH (4.6-8)
• Specific Gravity (1.010-1.025)
• Others: bilirubin, leukocyte esterase, nitrite, glucose and ketones
Electrolytes
• Urine Sodium (varies widely)
• %FeNa - Fractional excretion of Sodium
• Potassium (varies widely)

Question 25

URINE PROTEIN/ALBUMIN

what does it assess?

Answer 25

○ Glomerulus is normally impermeable to large protein molecules such as albumin
○ Normally <100mg/24 hours
○ Three ways to measure protein - Urinary Albumin or Protein Excretion Rate (UAER or UPCR)
■ 24-hour urine collection
■ Estimated 24-hour urine excretion using a 4-hour timed urine collection
■ Urine dipstick

○ Albumin:Creatinine (ACR) Ratio (<2.0 mg/mmol)
○ Random urine spot test
○ Bottom line: Albuminuria/Proteinuria (specifically ACR) are helpful biomarkers to assess the progression of chronic kidney disease.

Question 26

CAUSES OF TRANSIENT ALBUMINURIA

Answer 26

● Recent major exercise
● Urinary tract infection
● Febrile illness
● Decompensated congestive heart failure
● Menstruation
● Acute severe elevation in blood glucose
● Acute severe elevation in blood pressure

Question 27

HOW SHOULD PHARMACISTS USE

RENAL LAB TESTS?

Answer 27

○Determine level of kidney function and
selection/dosing of certain types of medication.
○To monitor for adverse effects of some
medications
○Confirm type of acute kidney injury in
conjunction with patient history, other signs and
symptoms
○Confirm staging of chronic kidney disease and to
monitor progression