The document discusses methods of measuring and estimating glomerular filtration rate (GFR) to assess kidney function. It outlines two main methods - directly measuring GFR using exogenous or endogenous filtration markers in the blood or urine, and estimating GFR using equations like Cockcroft-Gault and MDRD study equation. While direct measurement is most accurate, estimated GFR using equations is sufficient for detecting, monitoring, and managing chronic kidney disease in most patients. Estimates are less accurate in populations without known chronic kidney disease.

1. PRESENTATION BY
DR. MUHAMMAD UMAIR

2. Review article
The 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.

3. the strengths and weaknesses
of current methods of measuring
and estimating GFR as applied to
chronic kidney disease.

4. Chronic Kidney Disease
A 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.

5. Measurement of GFR with
Filtration Markers
(urinary or plasma clearance)
• Exogenous: inulin,iothalamate,EDTA, and
iohexol.
• Endogenous: Creatinine, Cystatin C

6. EXOGENOUS MARKERS CLEARANCE

7. 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.

9. 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.

10. Estimation of GFR with Equations
Two creatinine-based equations
• The Cockcroft–Gault equation i.e
Ccr = [(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.

11. 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.

13. 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

15. When to Consider Clearance Measurements Instead
of 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

16. 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.

17. 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.