Clinical Laboratory Medicine and Kidneys

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Questions and Answers

What is the primary use of Blood Urea Nitrogen (BUN) testing?

To detect dehydration

To monitor renal function (correct)

To measure blood glucose levels

To assess liver function

What could a decreased BUN level indicate?

Renal failure

Dehydration

High protein diet

Liver damage (correct)

What does a BUN to SCr ratio greater than 20:1 suggest?

Intrinsic renal injury

Normal kidney function

Prerenal injury due to volume depletion (correct)

Dehydration without kidney impairment

Which of the following factors could cause elevated BUN levels?

Glomerular filtration dysfunction Signup and view all the answers

What is the purpose of the Cockcroft-Gault Equation?

To estimate creatinine clearance Signup and view all the answers

Which drugs are noted for their nephrotoxic effects?

Aminoglycosides Signup and view all the answers

What could a BUN level above normal levels indicate besides renal issues?

Upper gastrointestinal bleed Signup and view all the answers

In the context of renal function, what is significant about drugs that require renal dose adjustments?

They may require therapeutic drug monitoring Signup and view all the answers

What is the main functional unit of the kidneys?

Nephron Signup and view all the answers

Which of the following substances is primarily excreted by the kidneys?

Water Signup and view all the answers

What does the Cockcroft-Gault equation primarily estimate?

Glomerular filtration rate Signup and view all the answers

Which of the following is a prerenal cause of kidney injury?

Decreased blood flow Signup and view all the answers

Which marker is considered an endogenous marker of kidney function?

Cystatin C Signup and view all the answers

What is the normal glomerular filtration rate (GFR) in mL/min?

120 Signup and view all the answers

Which cell type is commonly analyzed in urinalysis for signs of infection?

Leukocytes (WBC) Signup and view all the answers

What role does creatinine play in relation to kidney function?

It is a by-product of muscle metabolism. Signup and view all the answers

What does proteinuria indicate in a urine test?

Kidney damage or disease Signup and view all the answers

Which statement about renal plasma flow is true?

It is approximately 625 mL/min. Signup and view all the answers

What does azotemia refer to?

Elevated levels of nitrogen-containing compounds in blood Signup and view all the answers

Which condition is associated with postrenal kidney injury?

BPH (Benign Prostatic Hyperplasia) Signup and view all the answers

In a 'basic metabolic panel', which parameter commonly indicates kidney function?

Blood urea nitrogen (BUN) Signup and view all the answers

Which body weight should be used in the Cockcroft-Gault equation if the actual body weight (ABW) is significantly larger than Ideal Body Weight (IBW)?

Adjusted body weight Signup and view all the answers

Study Notes

Introduction to Clinical Laboratory Medicine and Kidneys

The presentation is on clinical laboratory medicine and the kidneys
The professor is Nathan Cope, PharmD, BCPS
The location is South College School of Pharmacy

Learning Objectives

Describe normal kidney physiology and how it relates to handling substances monitored by laboratory tests
Understand the utility, usefulness, and limitations of common laboratory tests for renal function
Estimate creatinine clearance using the Cockcroft-Gault equation given patient demographics and lab values
Know major components of a urinalysis
Understand what results from macroscopic, microscopic, and chemical analysis of urine indicate
Appreciate the pharmacist's role in patient care regarding laboratory tests related to the kidneys

Common Terms and Abbreviations

Glomerulus: Part of the nephron
Afferent arteriole: Blood vessel that enters the glomerulus
Efferent arteriole: Blood vessel that leaves the glomerulus
Loop of Henle: Part of the nephron
Distal Convoluted Tubule: Part of the nephron
Collecting Duct: Part of the nephron
CKD (chronic kidney disease): A disease of the kidneys
BMP (basic metabolic panel): Blood test that measures various substances in the blood
SCr (serum creatinine): Measure of creatinine in the blood
Creatine: A substance that helps with energy storage in muscles
CrCl (creatinine clearance): Measure of how well the kidneys remove creatinine from the blood
Cockcroft-Gault: An equation used to estimate creatinine clearance
BUN (blood urea nitrogen): Measure of urea in the blood
Prerenal: Before the kidneys
Intrarenal: Within the kidneys
Postrenal: After the kidneys
MDRD (Modification of Diet in Renal Disease): A method to estimate GFR
GFR (glomerular filtration rate): A measure of the kidney's function
Azotemia: Elevated BUN levels
Erythrocytes: Red Blood Cells
RBC: Red Blood Cells
Leukocyte: White Blood Cells
WBC: White Blood Cells
Leukocyte esterase: An enzyme produced by white blood cells in the urine
Casts: Cellular debris formed in the tubules of the kidney.
Tubular epithelial cells: Cells lining the kidney tubules
Proteinuria: Protein in the urine
Nitrite: A product of bacterial activity in the urinary tract.
Specific gravity: Density of urine
UTI (urinary tract infection): Bacterial infection in the urinary tract
Bacteriuria: Bacteria in the urine

Outline

Review of Kidney Anatomy and Physiology
Renal Assessment
- Estimating function
- Serum Creatinine and Cockcroft-Gault
- Blood Urea Nitrogen
Medications and Renal Elimination
Components of a urinalysis
- Macroanalysis
- Microanalysis
- Chemical analysis

Role of the Kidneys

Maintain homeostasis
Excretion/elimination of water, electrolytes, metabolic by-products, and drugs
Substance activation and synthesis, regulation of blood pressure and metabolism
Red blood cell production

Renal Anatomy and Physiology

Nephron: Functional unit of the kidney
Each kidney contains ~1 million nephrons
Arterioles: Afferent and efferent
Glomerulus (Bowman's Capsule): Site of filtration
Proximal tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
Glomerular filtration
Tubular reabsorption
Tubular secretion

Kidney Injury

Prerenal: Blood flow to the kidneys is reduced
Intrarenal (Intrinsic): Injury within the kidney
Postrenal: Blockage after the kidneys

Assessment of Kidney Function

Markers of Clearance
- Exogenous markers (inulin, i-iothalamate, Cr-EDTA)
- Endogenous markers (serum creatinine, cystatin C)
Creatinine equations: Cockcroft-Gault equation, GFR-MDRD equation, Cystatin C
Creatinine and timed urine collection

Muscle and Serum Creatinine

Creatine and creatine phosphate are energy sources for muscle
Creatinine is a by-product of muscle metabolism
Rate of serum creatinine production is constant for a given muscle mass.
Creatinine clearance is a measure of how well the kidneys filter creatinine; it serves as a surrogate for GFR.
Cockcroft-Gault Equation is a historical gold standard for drug dosing.

Creatinine Clearance (CrCl)

Creatinine clearance is a measure of how well the kidneys remove creatinine from the blood
Relationship between serum creatinine and creatinine clearance

Ideal Body Weight (IBW)

Used in calculating appropriate weight for Cockcroft-Gault Equation.

Cockcroft-Gault Equation

Used to estimate creatinine clearance
Factors to calculate creatinine clearance include ideal body weight, serum creatinine level, and gender.
Modifications for adjusted body weight and elderly patients.

In-Class Examples

Examples given for the calculation of IBW, percentage of IBW and adjusted body weight, if needed using Cockcroft-Gault Equation

Blood Urea Nitrogen (BUN)

Concentration of urea in the serum
Urea is renally cleared, but influenced by multiple factors
Used to monitor renal function, hydration, protein tolerance, and catabolism
Urea reabsorption parallels water and sodium retention.
Elevated BUN (azotemia) can be caused by high protein diet, upper gastrointestinal bleed, and certain drugs
Decreased BUN could indicate malnourishment

BUN and Prerenal Injury

Ratio of BUN to SCr can help distinguish between different types of kidney injury.
High BUN:SCr ratio suggests prerenal injury
Lower BUN:SCr ratio suggests intrarenal injury

Renal Function and the Pharmacist

Nephrotoxic drugs need careful monitoring
Dose adjustments are required for drugs eliminated by the kidneys
Pharmacists need to assess factors beyond just numbers when managing patients with kidney dysfunction

Urinalysis

Screening tool during hospital/office visits.
Proper collection is vital for reliable results
Urinalysis consists of macroscopic, microscopic, and chemical analysis
Components of a urinalysis including color, turbidity, formed elements (cells, casts), and chemical components measured using chemical analysis.

Urinalysis: Macroscopic

Includes color and turbidity
Color changes may indicate certain drugs or diseases
Turbidity can suggest the presence of precipitates

Examples of Urine Discoloration

Various drugs and conditions can cause urine discoloration.

Urinalysis: Microscopic (formed elements)

Includes microorganisms, cells, casts, and crystals in urine samples.
- Preparation involves using a 12 ml sample, centrifuging it and examining under microscopic magnification.
- Components examined include:
  - Microorganisms
  - Red blood cells
  - White blood cells
  - Casts (hyaline, cellular, granular, waxy)
  - Crystals (many types)

Cells (Microscopic, continued)

Microorganisms: contamination
Red blood cells: hematuria signals problems
White blood cells: associated with UTIs
Tubular epithelial cells: inflammation or acute tubular necrosis

Casts (Microscopic)

Hyaline casts: associated with prerenal azotemia, strenuous exercise, or no specific cause
Cellular casts: related to various kidney diseases
Granular and Waxy Casts: advanced kidney conditions

Crystals (Microscopic)

Various types of crystals are analyzed

Urinalysis: Chemical

Semiquantitative tests use chemstrips to identify various components in the urinalysis.
Components assessed here include: Specific gravity, protein, bilirubin, bile, glucose, urobilinogen, blood, ketones

Summary

Understanding kidney function relates to the appropriate interpretation of clinical tests
Lab tests and equations help assess kidney function but must be considered together with other clinical factors
Components of a urinalysis and results can guide appropriate clinical decision making.
Information regarding renal function is very important in patient care and guiding pharmaceutical care.

Additional Information (FYI only)

Urinary Sodium
Interpret in relation to water reabsorption
Fractional Extraction of Sodium (%FENa)
Timed Urine Collection
Reports in ml/min/1.73 m²
Ucr = urine creatinine
V = volume of urine
T = time collected
BSA = body surface area
GFR-abbreviated MDRD Equation
Reports in ml/min/1.73 m²

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Description

This quiz focuses on the fundamentals of clinical laboratory medicine as it pertains to kidney function. Participants will explore kidney physiology, laboratory tests for renal function, and the significance of urinalysis. Additionally, the pharmacist's role in interpreting these tests will be highlighted.