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Questions and Answers
Which lipoprotein is characterized by a higher cholesterol content contributing to its lower density compared to VLDL?
What is the primary characteristic of LP(a) that distinguishes it from typical VLDL?
In the context of lipoproteins, what does IDL stand for?
Which of the following lipoproteins is primarily associated with obstructive biliary disease?
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Which lipoprotein is known to have an electrophoretic mobility similar to VLDL despite differing in density?
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What primarily indicates the glomerular filtration rate (GFR)?
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Which of the following formulas correctly calculates clearance for a substance?
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What does a decrease in glomerular filtration rate typically indicate?
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What is the primary advantage of using creatinine clearance as a measure of renal function?
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Which method is used for the direct measurement of serum urea concentration?
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How is the concentration of urea in the blood calculated from BUN?
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Which of the following statements is true regarding creatinine as a renal function index?
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What is the significance of Cystatin C in assessing kidney function?
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What is the reference value for male inulin clearance?
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Which process directly influences creatinine clearance?
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What is the drawback of using urea clearance to estimate GFR?
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How does cystatin C function in relation to kidney function assessment?
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Which factor leads to an increased creatinine clearance rate?
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What is the approximate ratio of urea clearance to creatinine clearance in normal renal function with blood volume depletion?
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What is a characteristic of inulin clearance as a reference method?
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Which statement about the effects of diet on urea clearance is true?
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What is a common condition associated with decreased creatinine clearance?
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Which method is used for calculating VLDL levels using triglycerides?
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What is the primary purpose of measuring creatinine clearance?
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Which of the following statements about the BUN/creatinine ratio is correct?
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In what condition would you expect an increased uric acid level?
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Which factor contributes to decreased creatinine clearance?
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What is the significance of measuring Cystatin C levels in clinical practice?
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What is the primary method for assessing Glomerular Filtration Rate (GFR)?
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Which enzyme catalyzes the conversion of creatinine to sarcosine?
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Which analytical method is considered less specific for measuring creatinine and may yield falsely elevated results?
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Which of the following is not a source of uric acid in the body?
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What is typically observed in a patient with low glomerular filtration rate (GFR)?
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Which method uses saponification with alcoholic KOH for cholesterol measurement?
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What is the reference value for desirable cholesterol levels?
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Which age group has a high risk cutoff point of >260 mg/dL for cholesterol?
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In the enzymatic method of triglyceride measurement, what is the first enzyme involved?
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Which of the following measurements involves a colorimetric reaction with HCHO and chromotropic acid?
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What is the enzymatic reaction following glycerophosphate in triglyceride analysis?
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Which method involves using potassium bromide for ultracentrifugation in HDL-C measurement?
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What is a common outcome of enzymatic assays of cholesterol that follow the oxidation process?
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For the age group 20-29 years, what is considered a moderate risk for cholesterol levels?
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Which of the following is the result of cholesterol oxidase activity?
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Study Notes
Glomerular Filtration Rate (GFR)
- A measure of kidney function, representing the volume of blood filtered by the kidneys per minute.
- Expressed in milliliters per minute (mL/min).
- Decreases with age, roughly 1.0 mL/min/yr after 20-30 years old.
- Indicates the kidneys' ability to remove waste products and excess fluid from the bloodstream.
Clearance
- Represents the volume of plasma contributing to the excreted solute.
- Represents the removal of substance from plasma into urine over a set time.
- Expressed in mL/min.
- Inversely proportional to plasma concentration - as clearance decreases, plasma concentration increases.
GFR Formula
- Clearance (mL/min) = (U x V x 1.73) / (P x minutes)
- U = analyte concentration in urine (mg/L)
- P = analyte concentration in plasma (mg/L)
- V = urine volume in mL over 24 hours
- Minutes = time required to collect urine (1440 minutes)
- 1.73 = patient's body surface area
Blood Urea Nitrogen (BUN)
- Major end product of protein and amino acid catabolism used to estimate urea concentration.
- Urea (mg%) = 2.14 x BUN
- Measured using:
- Chemical (direct): Measures urea concentration in blood.
- Enzymatic (indirect): Uses an enzyme to convert urea to a measurable product.
- IDMS (isotope dilution mass spectrometry): Reference method for calibrating urea assays.
Creatinine
- End product of muscle metabolism derived from creatine.
- Commonly used to monitor renal function and index overall renal function.
- Reference value: 0.5-1.5 mg/dL (44-133 umol/L)
- Used to evaluate fetal kidney maturity.
- Fasting not required for testing.
- Hemolyzed or icteric samples should be avoided.
Creatinine Clearance
- Excellent measurement of renal function, as creatinine is freely filtered by the glomerulus but not reabsorbed.
- Reference value:
- Male: 85-125 mL/min
- Female: 75-112 mL/min
- Factors increasing creatinine clearance:
- High cardiac output
- Pregnancy
- Burns
- Factors decreasing creatinine clearance:
- Impaired kidney function
- Shock, dehydration
- Hemorrhage
- Congestive heart failure
Inulin Clearance
- Reference method for GFR but not routinely used due to continuous IV infusion requirements.
- Priming dose: 25mL of 10% inulin
- Continuous infusion: 500mL of 1.5% inulin
- Reference value:
- Male: 127 mL/min
- Female: 118 mL/min
Urea Clearance
- Does not provide a reliable estimate of GFR.
- Freely filtered by the glomerulus but variably reabsorbed by the tubules, making it unreliable.
- Affected by:
- Protein diet
- Enzymatic method affected by smoking due to ammonia
- Significant in demonstrating progression of renal disease and assessing response to treatment.
Cystatin C
- Freely filtered by the glomerulus, not secreted by the renal tubules but reabsorbed.
- Completely reabsorbed in the proximal convoluted tubule (PCT).
- Its presence in the urine is an indirect measure of GFR.
- Tubule-serum level is consistent, averaging for an adult individual's body surface area.
Uric Acid
- Major product of purine (adenine and guanine) catabolism, the final breakdown product of nucleic acid catabolism.
- Formed from xanthine by xanthine oxidase in the liver and intestines.
- Filtered, partially reabsorbed, and secreted by the renal tubules.
- Derived from:
- Catabolism of ingested nucleoproteins
- Catabolism of endogenous nucleoproteins
- Direct transformation of endogenous purine nucleotides.
- Approximately 1g of uric acid is excreted daily.
- Reference values:
- Male: 3.5-7.2 mg/dL (0.21-0.43 mmol/L)
- Female: 2.6-6.0 mg/dL (0.16-0.36 mmol/L)
Minor & Abnormal Lipoproteins
Intermediate-density Lipoprotein (IDL)
- Also known as "Floating Beta-lipoprotein".
- Has the same electrophoretic mobility as LDL but is less dense due to higher cholesterol content.
- Associated with type III hyperlipoproteinemia (dysbetalipoproteinemia).
Lipoprotein(a) [Lp(a)]
- Also known as "Sinking Pre-B lipoprotein".
- Structurally similar to LDL.
- Has electrophoretic mobility similar to VLDL.
- Ultracentrifugation sinks lower than LDL due to high protein content.
- Contains apo(a), a prothrombotic protein homologous to plasminogen.
- Inhibits fibrinolysis, competing with fibrinogen for binding sites on clots.
- Contributes to cardiovascular disease by increasing risk of blood clots (e.g., MI, stroke).
Lipoprotein X (LPX)
- Associated with obstructive biliary disease and LCAT deficiency.
- Primarily composed of cholesterol esters.
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Description
Test your knowledge on glomerular filtration rate (GFR), clearance, and the formulas used to evaluate kidney function. This quiz covers essential concepts including blood urea nitrogen and the effects of aging on kidney performance. Challenge yourself to understand how these metrics relate to overall health.
