The document discusses renal function tests and their interpretation. It provides information on various tests used to evaluate kidney function, including blood urea nitrogen, serum creatinine, and creatinine clearance. It defines different types of azotemia and outlines stages of chronic kidney disease based on estimated glomerular filtration rate and albumin-creatinine ratio. The document also discusses equations used to estimate glomerular filtration rate, including MDRD4, CKD-EPI, Cockcroft-Gault, and Jelliffe, noting their uses and limitations.

1. Interpretation of
Renal Function Tests

2.  Renal Functions Tests (RFTs) can be assessed by measuring Blood
Urea Nitrogen (BUN), Serum Creatinine (SCr). and Creatinine
Clearance (CrCl or ClCR);
 In many disease conditions, urea and creatinine accumulate in the
blood as they cannot be excreted properly.
 The RFTs basically evaluate the Glomerular Filtration Rate (GFR).
 Renal Function decreases with age and disease condition. Consider
these while interpreting the test values.
 RFTs can help in determining the dosage for medications excreted
through the kidneys.

3.  Azotemia: Excessive retention of nitrogenous waste products (BUN
and creatinine) in the blood.
 Uremia: the syndrome resulting from decreased renal function
and azotemia;
 Azotemia types:
Renal azotemia
• Due to renal
diseases like
glomerulonephritis
and pyelonephritis
Pre-renal azotemia
• Due to severe
dehydration,
hemorrhagic shock,
excessive protein
intake
Post-renal azotemia
• Due to stones
(ureteral, urethral),
tumors, prostatic
obstructions

4. Blood Urea Nitrogen (BUN)
 Urea is an end product of protein metabolism.
 Is produced by the liver and excreted by the kidneys;
 Urea is filtered by the glomerulus; tubules reabsorb approx. 40%.
 Normal BUN range: 3.0 – 6.5 mmol/L (8 – 18 mg/dL)
 ↑ed BUN levels indicate renal disease.
 ↓ed BUN levels indicate hepatic disease.

5. Serum Creatinine
 Is a more sensitive indicator of renal damage than BUN levels
because renal impairment is almost the only cause of an increase
in serum creatinine levels.
 Normal SCr range: 50 – 110 mmol/L (0.6 – 1.2 mg/dL)

6. Clearance
 Is a theoretical concept used to estimate GFR;
 The volm. of plasma from which a measured amount of substance
(solutes, drugs, etc..) can be completely eliminated or cleared into
the urine per unit time.
 Creatinine: Endogenous amine produced by muscle catabolism;
excreted unchanged by GF only;
Creatinine Clearance (CrCl or ClCR)
 Is the rate at which creatinine is removed from the blood by the
kidneys;
 This provides the approximate value of the GFR in ml/min.
 Normal range: 75-125 ml/min.
 CrCl depends on age, gender, weight, disease state, among other
factors.

8. Issue with CrCl formula:
 Some creatinine found in the urine is due to ‘Tubular
Secretion’.
 CrCl formula therefore overestimates GFR at all levels
of renal function.
 Drugs (like amiloride, cimetidine, trimethoprim,
salicylates, triamterene, spironolactone) which inhibit
secretory function may increase SCr, and decrease the
overestimate, without actually affecting the GFR.

9.  Renal Function is calculated by:

10. Chronic Kidney Disease
Definition:
 A CKD patient has abnormalities of kidney function or
structure present for > 3 months.
 The definition of CKD includes…
• all individuals with markers of kidney damage, or
• those with an eGFR of < 60 ml/min/1.73m2 on at least
2 occasions 90 days apart (with or without markers of
kidney damage).

12. The K/DOQI classification of CKD
K/DOQI = Kidney Disease Outcome Quality Initiative;
(by the National Kidney Foundation)

13. Markers of kidney disease:
 Albuminuria (ACR > 3 mg/mmol),
 Haematuria (or presumed or confirmed renal origin),
 Electrolyte abnormalities due to tubular disorders,
 Renal histological abnormalities,
 Structural abnormalities detected by imaging (e.g.
polycystic kidneys, reflux nephropathy)
 H/o kidney transplantation;

16. CKD Classification
 Based on the eGFR and the level of proteinuria and helps to
risk-stratify patients.
 Patients are classified as…
• G1-G5 (based on the eGFR), and
• A1-A3 (based on the ACR which is albumin:creatinine ratio)
 E.g.,
• A person with an eGFR of 25 ml/min/1.73 m2 and an ACR of 15
mg/mmol has CKD G4A2.
• A person with an eGFR of 50 ml/min/1.73 m2 and an ACR of 35
mg/mmol has CKD G3aA3.

19. KDIGO stages of CKD
 Stage 1 GFR > 90 ml/min/1.73 m²
 Stage 2 GFR 60 – 89 ml/min/1.73 m²
 Stage 3a GFR 45 – 59 ml/min/1.73 m²
 Stage 3b GFR 30 – 44 ml/min/1.73 m²
 Stage 4 GFR 15 – 29 ml/min/1.73 m²
 Stage 5-GFR <15 ml/min/1.73 m² (ESRD)
• KDIGO = Kidney Disease Improving Global Outcomes
• ESRD = End-Stage Renal Disease

21.  In pts. w/ CKD stages 1 – 5 (pre-dialysis), the
Cockroft-Gault (CG) eqn. is used to estimate the CrCl
in the presence of stable renal function.
(140-age) x (W)
CrCl = ______________
(72) x SCr
CrCl (females) = CrCl (males) x 0.85
 where, SCr is in mg/dl and W is in kgs

22.  MDRD4 equation:
• Where, eGFR = estimated GFR (ml min-1/ 1.73 m2 BSA)
• (Cs)cr = serum creatinine conc.(mg/dl)
 If serum albumin (ALB) and BUN values are known,
then the formula can be expressed as:
• (Cs)cr and BUN units is mg%; ALB is %

23. MDRD4 eqn. limitations:
 Underestimates eGFR for patients with GFR > 60
ml/min
 MDRD4 eqn. is not adjusted for body weight…
Smaller eGFR values for heavy patients,
Larger eGFR values for thinner patients
vs CG eqn.

24. Drug classes requiring dosage adjustment in CKD

25. CKD-EPI Equations for calculation of eGFR
CKD-EPI creatinine equation (Levey, et. al.)
eGFR = 141 x min(SCr/κ, 1)α x max(SCr /κ, 1)-1.209 x
(0.993)Age x [1.018 if female] x [1.159 if Black]
• eGFR (mL/min/1.73 m2); SCr = standardized serum creatinine (mg/dL)
• κ = 0.7 (females); 0.9 (males); α = - 0.329 (females), - 0.411 (males)
• min = indicates the minimum of SCr/κ or 1
• max = indicates the maximum of SCr/κ or 1
 The CKD-EPI eqns. are mainly used for identifying CKD
and staging the degree of severity.
 More accurate than the MDRD4 equation, especially for
patients with higher levels of GFR.
 Not yet being used in Malaysia.

26. CKD-EPI Equations for calculation of eGFR (contd’.)
CKD-EPI cystatin C equation (Inker, et. al.)
eGFR = 133 x min(SCys/0.8, 1)-0.499 x max(SCys /0.8, 1)-1.328 x
(0.996)Age x [0.932 if female]
• eGFR (mL/min/1.73 m2); SCys = standardized serum cystatin C
CKD-EPI creatinine-cystatin C equation (Inker, et. al.)
eGFR = 135 x min(SCr/k, 1)-a x max(SCr /k, 1)-0.601 x
min(SCys/0.8, 1)-0.375 x max(SCys /0.8, 1)-0.711 (0.995)Age x
[0.969 if female] x [1.018 if Black]
K = 0.7 (females), 0.9 (males);
a = -0.248 (females), -0.207 (males)

27.  Jelliffe Equation:
CrCl (ml/min) = {[98 – 0.8 × (age – 20)] × [1 – (0.01 × gender)]
× (BSA/1.73)}/(SCr × 0.0113)
• BSA = Body Surface Area;
• SCr = Serum Creatinine;

28. THE END