Assessing kidney function — measured
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Transcript of Assessing kidney function — measured
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PRESENTATION BY
DR. MUHAMMAD UMAIR
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Review articleThe new england journal of medicine
Assessing Kidney Function-Measured and Estimated Glomerular Filtration Rate
Lesley A. Stevens, M.D., Josef Coresh, M.D., Ph.D., Tom Greene, Ph.D.,and Andrew S. Levey, M.D.
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the strengths and weaknessesof current methods of measuring and estimating GFR as applied to chronic kidney disease.
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Chronic Kidney DiseaseA persistent reduction in the GFR to less than 60 ml per minute per 1.73m2of body-surface area
or
the presence of kidney damage, regardless of the cause, for three or more months.
Risk factors:
an age of more than 60 years, hypertension, diabetes, cardiovascular disease, and a family history of the disease.
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Measurement of GFR with Filtration Markers
(urinary or plasma clearance)
• Exogenous: inulin,iothalamate,EDTA, and iohexol.
• Endogenous: Creatinine, Cystatin C
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EXOGENOUS MARKERS CLEARANCE
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ENDOGENOUS MARKERS:Creatinine
• Urinary clearance:timed urine collection
• blood sampling during the collection period
• Creatinine clearance has reciprocal relationship with the serum creatinine level.
• Drugs, trimethoprim & cimetidine clearance and serum level
• the relationship between the levels of serum creatinine and GFR varies among persons & over time.
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Cystatin C• Reabsorbed and catabolized by the tubular
epithelial cells; only small amounts are excreted in the urine so its urinary clearance cannot be measured.
• The generation of cystatin C appears to be less variable from person to person than that of creatinine.
• However, serum levels are Influenced by corticosteroid use and related to age, sex, weight, height, smoking status, and the level of C-reactive protein.
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Estimation of GFR with Equations
Two creatinine-based equations
• The Cockcroft–Gault equation i.eCcr = [(140 − age) × weight]/(72 × Scr ) × 0.85 (if the subject is female)
• The Modification of Diet in Renal Disease (MDRD) study equation i.e
GFR = 186 × (Scr)−1.154 × (age)−0.203 × 0.742 (if the subject is female)
or × 1.212 (if the subject is black).
It estimates GFR adjusted for body-surface area. It was found to be more accurate.
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Evaluation of Current Estimating Equations
• In some studies the MDRD study equation has been reported to be more accurate than the Cockcroft–Gault equation but not in other.
• The Cockcroft–Gault equation appears to be less accurate than the MDRD study equation in older and obese people
• The MDRD study equation is reasonably accurate in nonhospitalized patients known to have chronic kidney disease
• Both the MDRD study and the Cockcroft–Gault
equations have been reported to be less accurate
in populations without chronic kidney disease.
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Use of GFR Estimates
• Detection of Chronic Kidney Disease
• Monitoring Progression of Chronic Kidney Disease
• Evaluation and Management of Complications
• GFR and Referral to Nephrologists
• Medications and Chronic Kidney Disease
• Assessment of Risk for Cardiovascular Disease
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When to Consider Clearance Measurements Insteadof Estimated GFR
When more accurate estimates
may be necessary
• to evaluate people for kidney donation,
• to administer drugs (e.g.methotrexate), or
• for research protocols.
Clearance of exogenous filtration markers provides
the most accurate measure of GFR
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GFR Reporting by Clinical Laboratories
• Laboratories should report a specific value of GFR only if the estimated GFR is less than 60 ml per minute per 1.73 m2
• Higher values should be reported as “GFR is 60 ml per minute per 1.73 m2 or more.
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Conclusions
• The main limitation of current GFR estimates is
the greater inaccuracy in populations without
known chronic kidney disease than in those with
the disease.
• However current GFR estimates
facilitate detection, evaluation, and management
of the disease.
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