RENAL FUNCTION TESTS (RFT)

1. INTERPRATATION OF DIAGNOSTIC TESTS
RENAL FUNCTION TEST
Kedir.N
June, 2023
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2. ANATOMY
 Highly differentiated organ
 Renal blood flow normally drains ~20% of the
cardiac output, or1000 mL/min.
 Filtration is determined by
molecular size to lesser
extent by charge
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PHYSIOLOGY

4. GLOMERULUS
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5. Afferent renal arteriole
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9. gfr
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Glomerular filtration rate (GFR)
 is the product of the average filtration rate of each nephron
 normal level for GFR is approximately 130 ml/min/1.73 m² for men and
120 ml/min/1.73 m² for women

10. gfr
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• GFR correlates well with
 health and disease
• Both tubular secretion and absorption
• Endocrine and metabolic function of the kidney

11.  Plasma clearance of substance x (Cx) can be
calculated as Cx = Ax/Px
 AX - eliminated amount of substance x
 Px – plasma level of substance x
 In the steady state, substance x is maintained at
constant plasma level.
 To decrease non-GFR determinants equations
use clinical and epidemiologic variables giving
more accurate estimated GFR.
 Other sources of error
 Measurement error - Poor
calibration
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12. gfr
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Endogenous chemicals used to estimate GFR
 Solutes that are <20,000Da, not bound with plasma proteins, freely
filtered by the glomerulus
 Endogenous – usually produced in a steady state
 Creatinine
 Urea, cystatin c
 Exogeneous
 Inulin
 Iothalamate, iohexol, ethylenediaminetetraacetic acid, and diethylenetriaminepentaacetic acid


13. Gfr
 Factors affecting GFR
 Age
 Gender
 body size
 physical activity
 diet,
 pharmacotherapy,
 Hyperglycemia
 physiologic states such as
pregnancy
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14. gfr
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 Age – decline with age; the mean rate of decline is approximately 0.75 ml/min/year after 40 years of
age.
 Gender – 8% higher in men than women
 body size – BSA is used to counter the body size of the body (/ml min/1.73m²)
 physical activity, diet, pharmacotherapy, hyperglycemia, and physiologic states such as


15. gfr
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 Pregnancy - GFR increases by about 50% in the first trimester and returns to normal immediately
after delivery
 Diurnal variation - and is 10% lower at midnight compared with the afternoon
 Reductions in GFR could result from
 Single nephron GFR decrement with-out loss of nephron number
 Due to loss of nephrons

16. creatinine
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 Creatinine is
 Metabolite of phosphocreatine from muscle
 Free not protein bound,
 Freely filtered across glomerulus
 Secreted by tubules
 drugs that affect creatinine level
 cimetidine, trimethoprim, and possibly fenofibrate
 Some cephalosporins and flucytosine
 Cystatin C – cellular product

17. gfr
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 GFR calculation equations
 Cockcroft-Gault formula
 CrCl = [(140 - age) x IBW] / (Scr x 72) (x 0.85 for females)
 IBW calculator =
 MDRD equation
 Estimated GFR (ml/min/1.73m2) = 186 x (Scr/ 88.4)-1.154 x (Age)-
0.203 x (0.742 if female) x (1.210 if black)
 CKD-EPI equation
 GFR = 141 × min(Scr/κ, 1)α × max(Scr/κ, 1)-1.209 × 0.993Age × 1.018
[if female] × 1.159 [if African American]

18. gfr
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 Still GFR calculations don’t consider
 extreme levels for creatinine generation
 amputees
 large or small individuals
 muscle-wasting conditions
 atypical pattern of meat consumption

19. DRUG DOSING AND RENAL FUNCTION
TEST
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 Pharmacokinetics of many drugs is affected by acute and
chronic disease
 Drug dosing calculation with MDRD equation should use ml/min
than /1.73m²
 Body surface area =0.20247 x height (m)0.725 x mass (kg)0.425
 The Cockcroft-Gault formula was widely used.

20. AKI and drug dosing
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Recommendations for metabolized medications in AKI include
more close monitoring than current clinical practice
– Frequent monitoring of drug pharmacodynamics
– Therapeutic drug monitoring/pharmacokinetic analysis
• Limited by availability of laboratory testing in clinically
relevant time-frame

21. AKI AND DRUG DOSING
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 Duration of AKI may also be important
– Using dosing recommendations for CKD and ESRD early in AKI for drugs with a
significant nonrenal clearance component may lead to subtherapeutic levels
– Higher dosing may be needed early in course with later reduction in dose
and/or frequency as AKI persists and nonrenal clearance attenuates

22. Ckd and drug dosing
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 GFR is assumed to capture all aspects of effect of kidney yet
 No incorporation of other factors that may not correlate with GFR,
but are present in patients with CKD, e.g. hypoalbuminemia or drug
interactions

23. Reference
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Thank you!