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Questions and Answers
What does microalbuminuria indicate?
What does microalbuminuria indicate?
Which test is primarily used for screening chronic kidney disease (CKD)?
Which test is primarily used for screening chronic kidney disease (CKD)?
Which condition can cause eGFR to be misleading?
Which condition can cause eGFR to be misleading?
Which substance is measured in a standard renal function blood test?
Which substance is measured in a standard renal function blood test?
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What characterizes glomerular proteinuria?
What characterizes glomerular proteinuria?
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What is Cystatin C used for in kidney function tests?
What is Cystatin C used for in kidney function tests?
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Which of the following is NOT a function of the kidneys?
Which of the following is NOT a function of the kidneys?
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In what scenario might high eGFR values be misleading?
In what scenario might high eGFR values be misleading?
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What factor does NOT significantly influence the plasma concentration of the substance filtered by the glomerulus?
What factor does NOT significantly influence the plasma concentration of the substance filtered by the glomerulus?
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Which condition is indicated by glycosuria with a normal blood glucose concentration?
Which condition is indicated by glycosuria with a normal blood glucose concentration?
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What is the primary use of beta 2 microglobulin in renal assessment?
What is the primary use of beta 2 microglobulin in renal assessment?
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What is a common screening test for early assessment of changes in GFR?
What is a common screening test for early assessment of changes in GFR?
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Which of the following is a reliable marker for assessing renal tubular damage?
Which of the following is a reliable marker for assessing renal tubular damage?
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Which condition is NOT associated with increased levels of beta 2 microglobulin?
Which condition is NOT associated with increased levels of beta 2 microglobulin?
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Which test is used to assess renal concentrating ability?
Which test is used to assess renal concentrating ability?
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What does increased excretion of low-molecular-weight proteins in the urine suggest?
What does increased excretion of low-molecular-weight proteins in the urine suggest?
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What is the primary function of the kidneys related to waste?
What is the primary function of the kidneys related to waste?
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What does a microalbuminuria test specifically detect?
What does a microalbuminuria test specifically detect?
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Which test is commonly performed to assess kidney function via blood?
Which test is commonly performed to assess kidney function via blood?
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What is the typical range for heavy proteinuria indicating glomerular damage?
What is the typical range for heavy proteinuria indicating glomerular damage?
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Which factor may cause eGFR to be unreliable?
Which factor may cause eGFR to be unreliable?
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Which of the following statements about Cystatin C is true?
Which of the following statements about Cystatin C is true?
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What does a dipstick test primarily assess in urinalysis?
What does a dipstick test primarily assess in urinalysis?
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What condition is indicated by a positive dipstick for protein with low concentrations?
What condition is indicated by a positive dipstick for protein with low concentrations?
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What condition is associated with an increase in beta 2 microglobulin levels?
What condition is associated with an increase in beta 2 microglobulin levels?
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Which of the following statements about beta 2 microglobulin is correct?
Which of the following statements about beta 2 microglobulin is correct?
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What condition can cause glycosuria with a normal blood glucose concentration?
What condition can cause glycosuria with a normal blood glucose concentration?
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Which substance is included in some equations for estimating GFR?
Which substance is included in some equations for estimating GFR?
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What does increased excretion of low-molecular-weight proteins in urine indicate?
What does increased excretion of low-molecular-weight proteins in urine indicate?
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Which test is commonly used to assess proximal renal tubular function?
Which test is commonly used to assess proximal renal tubular function?
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What is the main characteristic of renal Fanconi syndrome?
What is the main characteristic of renal Fanconi syndrome?
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Which of the following is a key urinary test for distal tubular function?
Which of the following is a key urinary test for distal tubular function?
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Which type of proteinuria is characterized by heavy albuminuria indicating chronic kidney disease?
Which type of proteinuria is characterized by heavy albuminuria indicating chronic kidney disease?
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Which statement correctly describes microalbuminuria?
Which statement correctly describes microalbuminuria?
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In which condition might eGFR values be increased misleadingly?
In which condition might eGFR values be increased misleadingly?
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What factors are considered in calculating the estimated GFR (eGFR)?
What factors are considered in calculating the estimated GFR (eGFR)?
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Which of the following conditions does not interfere with eGFR accuracy?
Which of the following conditions does not interfere with eGFR accuracy?
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Cystatin C is primarily useful because it is influenced by what factor?
Cystatin C is primarily useful because it is influenced by what factor?
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Which of these is true about the implications of proteinuria?
Which of these is true about the implications of proteinuria?
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Which scenario is least likely to require monitoring kidney function tests?
Which scenario is least likely to require monitoring kidney function tests?
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What is the role of β2-microglobulin in assessing renal function?
What is the role of β2-microglobulin in assessing renal function?
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Which condition is most likely to cause an increase in cystatin C levels?
Which condition is most likely to cause an increase in cystatin C levels?
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Which test helps diagnose renal Fanconi syndrome?
Which test helps diagnose renal Fanconi syndrome?
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Which substance is most reliably used as a marker for renal tubular damage?
Which substance is most reliably used as a marker for renal tubular damage?
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What does increased urinary excretion of amino acids typically suggest?
What does increased urinary excretion of amino acids typically suggest?
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What is a common prognostic marker in multiple myeloma?
What is a common prognostic marker in multiple myeloma?
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Which test is essential for assessing the renal concentrating ability?
Which test is essential for assessing the renal concentrating ability?
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What can cause an unstable measurement of β2-microglobulin in urine?
What can cause an unstable measurement of β2-microglobulin in urine?
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What distinguishes post-renal causes of acute kidney injury (AKI) from pre-renal causes?
What distinguishes post-renal causes of acute kidney injury (AKI) from pre-renal causes?
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Which of the following is a common biochemical finding in acute kidney injury (AKI)?
Which of the following is a common biochemical finding in acute kidney injury (AKI)?
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Which of the following is NOT classified as a pre-renal cause of acute kidney injury (AKI)?
Which of the following is NOT classified as a pre-renal cause of acute kidney injury (AKI)?
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Intrinsic renal causes of acute kidney injury can be attributed to which of the following?
Intrinsic renal causes of acute kidney injury can be attributed to which of the following?
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What is a significant characteristic of acute kidney injury related to urine output?
What is a significant characteristic of acute kidney injury related to urine output?
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Which systemic disease is associated with intrinsic renal causes of acute kidney injury?
Which systemic disease is associated with intrinsic renal causes of acute kidney injury?
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In a clinical setting, which condition is most likely to present with decreased renal blood flow?
In a clinical setting, which condition is most likely to present with decreased renal blood flow?
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What is the implication of elevated serum urea levels in acute kidney injury?
What is the implication of elevated serum urea levels in acute kidney injury?
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What is a common feature of chronic kidney disease (CKD) related to electrolyte balance?
What is a common feature of chronic kidney disease (CKD) related to electrolyte balance?
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Which finding is typically associated with a very low eGFR in CKD?
Which finding is typically associated with a very low eGFR in CKD?
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What is the most likely cause of impotency in a patient with CKD?
What is the most likely cause of impotency in a patient with CKD?
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How does CKD affect glucose metabolism?
How does CKD affect glucose metabolism?
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What is the significance of elevated urea levels in a CKD patient?
What is the significance of elevated urea levels in a CKD patient?
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Which shift in electrolyte levels is most characteristic of CKD?
Which shift in electrolyte levels is most characteristic of CKD?
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What does a decreased eGFR typically indicate in the context of renal function?
What does a decreased eGFR typically indicate in the context of renal function?
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Which metabolic abnormality is commonly observed in patients with CKD?
Which metabolic abnormality is commonly observed in patients with CKD?
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What does concentrated, sodium-poor urine indicate in the context of kidney function?
What does concentrated, sodium-poor urine indicate in the context of kidney function?
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Which biochemical finding is typically elevated in pre-renal AKI compared to intrinsic renal injury?
Which biochemical finding is typically elevated in pre-renal AKI compared to intrinsic renal injury?
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What results would suggest intrinsic renal injury rather than pre-renal AKI?
What results would suggest intrinsic renal injury rather than pre-renal AKI?
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Which of the following is a common cause of chronic kidney disease?
Which of the following is a common cause of chronic kidney disease?
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What osmolality level is generally expected in the urine of patients with pre-renal AKI?
What osmolality level is generally expected in the urine of patients with pre-renal AKI?
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When diuretics are used, how can the interpretation of urinary osmolality in AKI be affected?
When diuretics are used, how can the interpretation of urinary osmolality in AKI be affected?
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Which of the following best describes oliguria in acute kidney injury?
Which of the following best describes oliguria in acute kidney injury?
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What implication does an increase in serum potassium to 5.6 mmol/L suggest in the context of AKI?
What implication does an increase in serum potassium to 5.6 mmol/L suggest in the context of AKI?
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What is a common biochemical finding associated with chronic kidney disease (CKD)?
What is a common biochemical finding associated with chronic kidney disease (CKD)?
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Which metabolic feature is commonly impaired in chronic kidney disease?
Which metabolic feature is commonly impaired in chronic kidney disease?
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What condition was least likely responsible for the patient's urine containing protein but no glucose?
What condition was least likely responsible for the patient's urine containing protein but no glucose?
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Which abnormality could result from decreased erythropoietin synthesis in CKD?
Which abnormality could result from decreased erythropoietin synthesis in CKD?
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What would most likely be observed in the lab results of a patient with advanced CKD?
What would most likely be observed in the lab results of a patient with advanced CKD?
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Which of these laboratory values is a potential indicator of electrolyte imbalance in CKD?
Which of these laboratory values is a potential indicator of electrolyte imbalance in CKD?
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What is a common symptom in patients with chronic kidney disease?
What is a common symptom in patients with chronic kidney disease?
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Which finding is indicative of impaired renal function in CKD due to reduced degradation of insulin?
Which finding is indicative of impaired renal function in CKD due to reduced degradation of insulin?
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What is the primary characteristic of acute kidney injury (AKI)?
What is the primary characteristic of acute kidney injury (AKI)?
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Which of the following is a pre-renal cause of acute kidney injury?
Which of the following is a pre-renal cause of acute kidney injury?
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Which finding is NOT typically associated with acute kidney injury (AKI)?
Which finding is NOT typically associated with acute kidney injury (AKI)?
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What lab result indicates a renal impairment related to intrinsic damage?
What lab result indicates a renal impairment related to intrinsic damage?
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Which of the following conditions can cause post-renal acute kidney injury?
Which of the following conditions can cause post-renal acute kidney injury?
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What is the significance of oliguria in the context of acute kidney injury?
What is the significance of oliguria in the context of acute kidney injury?
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Which laboratory finding is typically elevated in acute kidney injury?
Which laboratory finding is typically elevated in acute kidney injury?
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What is the typical urine sodium level expected in a dehydrated patient with pre-renal AKI?
What is the typical urine sodium level expected in a dehydrated patient with pre-renal AKI?
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What is indicated by low sodium levels and high urine osmolality in a patient with acute kidney injury?
What is indicated by low sodium levels and high urine osmolality in a patient with acute kidney injury?
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What factor can invalidate the interpretation of osmolalities in kidney injury?
What factor can invalidate the interpretation of osmolalities in kidney injury?
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Which of the following is a distinguishing feature of pre-renal acute kidney injury compared to intrinsic kidney injury?
Which of the following is a distinguishing feature of pre-renal acute kidney injury compared to intrinsic kidney injury?
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What can occur if pre-renal acute kidney injury is left untreated?
What can occur if pre-renal acute kidney injury is left untreated?
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In acute kidney injury, what is a more reliable indicator than urinary sodium concentration?
In acute kidney injury, what is a more reliable indicator than urinary sodium concentration?
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Which renal condition is primarily characterized by progressive, irreversible impairment of kidney function?
Which renal condition is primarily characterized by progressive, irreversible impairment of kidney function?
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Which substance's rise in serum concentration is often greater than that of creatinine in pre-renal acute kidney injury?
Which substance's rise in serum concentration is often greater than that of creatinine in pre-renal acute kidney injury?
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What is a common limitation in distinguishing between pre-renal and intrinsic renal injury?
What is a common limitation in distinguishing between pre-renal and intrinsic renal injury?
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Study Notes
Renal Function Tests
- Renal function tests assess kidney health
- Outcomes include evaluating biochemical kidney tests in disease states, and analyzing/interpreting kidney function tests in patients
- Assessment criteria include critically discussing glomerular filtration rate (GFR) equations, comparing/contrasting biochemical abnormalities in pre/renal/post-renal diseases, discussing urine analysis tests in renal disease workups, and analyzing/interpreting biochemical renal tests using clinical case vignettes
- Key resources include Marshall WJ, Lapsley M, Day A, Clinical Chemistry, 8th ed, Mosby, London, 2017
- No specific activities/assignments were mentioned
Kidney Function
- Excretion of waste products is a key function
- Maintaining extracellular fluid volume and composition, including acid/base balance, is crucial
- Hormone synthesis is also a significant function
- The nephron is the functional unit of the kidney.
- The main structural components include the glomerulus, proximal and distal tubules, loop of Henle, and collecting ducts.
Kidney Function Tests Available
-
Urinalysis:
- Dipstick test
- Microalbuminuria
-
Blood:
- Electrolytes (sodium, potassium, chloride)
- Urea
- Creatinine
- Cystatin C
- Beta 2 microglobulin
-
Equations:
- Creatinine clearance
- eGFR
Urinalysis (details)
- Values are shown in a table. The table illustrates different intensity levels for various components (e.g., blood, glucose, protein, bilirubin, nitrites). The table visually displays the range of values for each component.
Proteinuria
- Many positive dipsticks for protein are benign
- Microalbuminuria detects low albumin concentrations (30-300mg/day) indicative of early nephropathy (e.g., diabetic nephropathy)
- Positive dipsticks can be caused by substances exceeding normal reabsorption thresholds (e.g. Bence Jones protein), and certain kidney diseases.
Site of Damage (Proteinuria)
- Glomerular proteinuria: 2-3 grams/day (mainly albumin) frequently indicates chronic kidney disease (CKD) or other glomerular diseases
- Tubular proteinuria: less than 2 grams/day (low molecular weight proteins), including beta 2 microglobulin and retinol-binding protein. This indicates issues with the tubules' reabsorption of these proteins
- Overflow proteinuria: caused by high concentrations of low molecular weight proteins exceeding tubular reabsorptive capacity (e.g., Bence Jones protein, myoglobin). This can represent various underlying conditions.
Mechanisms of Proteinuria (Box 5.7)
- Overflow: Presence of high concentration of low molecular weight protein in plasma, exceeding tubular reabsorptive capacity. This includes substances like Bence Jones protein and myoglobin.
- Glomerular: Increased glomerular permeability (e.g., albumin, immunoglobulins). This signifies problems with the filtration process in the glomeruli.
- Tubular: Impaired or saturated reabsorption of filtered proteins by normal glomeruli (e.g., retinol-binding protein, a1-microglobulin). Problems with tubular reabsorption mechanisms are indicated.
- Secretory: Secretion by kidneys or urinary tract epithelium (e.g., uromodulin, other plasma proteins) due to urinary tract infections or bladder tumors. This indicates active protein release from the kidneys or urinary tract.
Protein Electrophoresis
- Used to identify proteinuria types (tubular, glomerular, or mixed) by separating proteins based on their electric charge.
Urea
- Synthesized in the liver
- Secreted and reabsorbed in the nephron
- Less specific than serum creatinine in assessing renal function
- Increased production due to high protein intake, catabolic states, or gastrointestinal bleeding. Can indicate increased nitrogenous waste.
- Decreased production in low-protein intake or liver disease. Can signal decreased metabolic activity or liver impairment
- Tubular reabsorption influences plasma urea concentration even with normal kidney function.
Creatinine
- Plasma creatinine concentration is a reliable test of glomerular function
- By-product of muscle energy metabolism; its production is directly linked to muscle mass.
- Mainly filtered by the kidneys, with some secretion.
- More sensitive and specific test of renal function than urea
- Reference intervals are gender-specific, reflecting muscle mass differences, and are important factors for evaluating results.
Elevated Plasma Creatinine
- Causes include massive rhabdomyolysis, diet (e.g., red meat), patient stature (body builders, adult males), and medications (e.g., probenecid, cimetidine, trimetoprime, amiloride) that block tubular secretion
- Interference can also come from cephalosporines and ketone bodies; these factors must be considered when interpreting results.
Low Plasma Creatinine
- Causes include age (elderly and infants), chronic illness, high bilirubin levels (falsely low lab values), and vegetarian diets (low creatine intake).
Creatinine Clearance
- Estimation of GFR: Involves measuring the urinary excretion of a substance completely filtered by the glomeruli, not secreted/reabsorbed/metabolized by the renal tubules
- Most widely used biochemical clearance test
- Based on creatinine measurements in plasma and urine
Creatinine Clearance Formula
- Clearance = (U x V) / P
- U = urine creatinine concentration (µmol/L)
- V = urine flow rate (mL/min or (L/24h)/1.44)
- P = plasma creatinine concentration (µmol/L)
Alternatives to Creatinine Clearance
- Two main approaches used:
- Deriving an estimated GFR (eGFR) from plasma creatinine concentration
- Using exogenous markers of clearance
Estimated GFR (eGFR)
- CKD-EPI, MDRD, and Cockcroft-Gault formulas are commonly used in clinical practice. These provide estimates are important for the assessment of kidney function but are not a direct measurement
- Different formulas address different populations and take into account sex, age, serum creatinine, and race. Clinical practice often relies on estimates of GFR (eGFR) because direct measurement is less convenient.
eGFR Misleading Circumstances
- AKI
- Increased distribution volume for creatinine (e.g., heart failure edema, nephrotic syndrome, pregnancy)
- Decreased muscle mass, such as in conditions like paraplegia, amputations, muscle loss, or significant malnutrition.
- Increased muscle mass (e.g., athletes, bodybuilders).
- Age extremes
- Ethnic groups (not validated across all groups).
- Malnutrition/obesity
- Meat-rich meals
- Medications that affect creatinine secretion (e.g., those that interfere with tubular secretion).
Cystatin C
- Tiny protein produced by all nucleated cells; freely filtered, reabsorbed, and catabolized in the proximal convoluted tubule.
- GFR estimation is more accurate than creatinine because less affected by muscle mass, age, and gender. Provides a more precise measure of kidney filtration.
- Useful for early changes in kidney function.
- Elevated in malignancies, hyperthyroidism, corticosteroid treatment. Can indicate underlying conditions impacting kidney function.
Beta 2 Microglobulin
- Freely filtered by the glomerulus and reabsorbed in the proximal tubule. Useful for GFR estimations.
- Sensitive marker for renal tubular disease, neoplasia, inflammation, and infectious conditions.
- Prognostic marker in multiple myeloma.
Tests for Renal Tubular Function
- Performed less frequently than glomerular function tests.
- Glycosuria with normal blood glucose suggests proximal tubular dysfunction (isolated or generalized).
- Aminoaciduria may occur with tubular defects.
- Assessments of proximal tubular bicarbonate reabsorption may be needed (e.g., proximal RTA).
- Protein filtration is almost completely reabsorbed and catabolized in the proximal renal tubules; this is important for normal function.
Tests for Distal Renal Tubular Function
- Increased excretion of low-molecular-weight proteins in the urine suggests renal tubular damage.
- Beta-2-microglobulin measurement is sometimes used (can be unstable).
- More reliable methods include retinol-binding protein or a1-microglobulin, which may not be required clinically if other data is sufficient. These alternative tests can be used when necessary or when other indicators are unavailable
- Water deprivation test assesses renal concentrating ability, and tests of urinary acidification are used for diagnosis of distal RTA
Conclusion
- Renal function tests provide insight into the state of the kidneys.
- GFR is the standard measure; eGFR estimation from plasma creatinine and cystatin C concentrations is used to avoid direct GFR measurements.
- Plasma analyte concentrations can indicate dehydration and tubular/glomerular defects.
- eGFR equations have improved GFR estimation accuracy and convenience, but caution is still needed in specific circumstances.
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Description
This quiz focuses on renal function tests assessing kidney health and disease states. It includes evaluating biochemical kidney tests, discussing glomerular filtration rates, and analyzing urine tests in renal disease. Participants will enhance their understanding of critical interpretations and applications in clinical scenarios.
