1. Novel Biomarkers of Kidney Disease NGAL and Cystatin C
COL SOHAIL SABIR
HOD NEPHROLOGY MILITARY HOSPITAL
HOD MEDICAL EDUCATION
ARMED FORCES POSTGRADUATE MEDICAL INSTITUTE

2. Biomarker
characteristic that is objectively measured and evaluated as an indicator of normal biological or pathogenic processes, or pharmacologic responses to a therapeutic intervention

3. serum creatinine unreliable indicator of acute kidney injury (AKI), for the following reasons:
influenced by multiple non-renal factors, such as age, gender, muscle mass, muscle metabolism, diet, medications, and hydration status
can take several hours or days to reach a new steady state and thus does not reflect the actual decrease in GFR in the acute setting
Because of renal reserve, the serum creatinine level may not rise until more than half of the kidney function has been lost

4. serum creatinine unreliable indicator of acute kidney injury (AKI), for the following reasons:
An increase in the serum creatinine level represents a delayed indication of a functional change in GFR that lags behind structural changes that occur in the kidney during the early stage of AKI
Serum creatinine measurement does not allow differentiation between hemodynamically mediated changes in renal function, such as pre-renal azotemia from intrinsic renal failure or obstructive uropathy

5. Characteristic of ideal marker of kidney disease
Ideally, biomarkers for kidney injury, especially in the acute setting, should have the following characteristics
Kidney specific and allow discrimination between pre-renal, intrinsic and post-renal causes of kidney injury
Able to detect kidney injury early in the course of the disease
Able to isolate the cause of kidney injury
Specific to particular sites in the kidneys and able to provide information on pathologic changes in the primary location of injury (eg, renal tubules, interstitium, vasculature)
Easily, reliably, promptly, and noninvasively measurable
Stable in its matrix
Inexpensive to measure

6. Novel Biomarkers of Acute Kidney Injury

7. Neutrophil Gelatinase-associated Lipocalin
NGAL is a 25-kD protein of the lipocalin family.
Elevation of NGAL levels in the plasma and urine of animal models of ischemic and nephrotoxic acute kidney injury
novel urinary biomarker for kidney injury

8. Neutrophil Gelatinase-associated Lipocalin
In human studies, the expression of the NGAL messenger ribonucleic acid (mRNA) and protein has been shown to be significantly increased in the kidney tubules in the following settings:
Ischemic, septic, or post-transplantation AKI
Within 2-6 hours after cardiopulmonary bypass surgery
At frequent intervals for 24 hours post–cardiopulmonary bypass surgery in children
Following contrast administration

9. NGAL reduce injury
inhibits apoptosis and increase the normal proliferation of kidney tubule cells and up-regulate heme oxygenase-1
which preserves proximal tubule N-cadherin
subsequently inhibits cell death

10. Translational Research Investigating Biomarker Endpoints in AKI study (TRIBE-AKI)
NGAL has been tested in multiple studies of patients at risk for AKI
to determine whether biomarkers measured at the time of first clinical diagnosis of early AKI after cardiac surgery can potentially predict AKI severity

11. Translational Research Investigating Biomarker Endpoints in AKI study (TRIBE-AKI)
Biomarkers such as urinary IL-18, urinary albumin-to-creatinine ratio (ACR), and urinary and plasma NGAL were demonstrated to improve risk classification compared with the clinical model alone
plasma NGAL performing the best
biomarkers measured on the day of AKI diagnosis improve risk stratification and identify patients at higher risk for progression of AKI and worse patient outcomes

12. diagnosis of early acute tubular necrosis (ATN) and differentiate it from pre-renal disease
Paragas et al
in a mouse strain with a gene for bioluminescence and fluorescence inserted into the NGAL gene
Imaging after ischemia reperfusion demonstrated illumination of specific cells of the distal nephron
Indicating NGAL production at the site of injury
No NGAL illumination was seen following maneuvers that lead to significant pre-renal disease

13. NGAL Vs IL-18
use of urinary neutrophil gelatinase–associated lipocalin (NGAL) and IL-18 in patients with AKI (post–cardiopulmonary bypass)
sequential markers: NGAL levels peak within the first 2-4 hours following AKI, while IL-18 peaks at the 12th hour.
A potential limitation of IL-18
more generalized marker of inflammation rather than a specific marker of AKI, particularly in the elderly population, who may have underlying baseline decreased kidney function.

14. Estimating GFR in Chronic Kidney Disease

15. Creatinine
Filtered primarily through the glomerulus, it may be used to estimate GFR when its generation and renal elimination are at steady state
The limitation of creatinine level as a marker of GFR is that its generation is highly heterogeneous across individuals and its tubular secretion may vary across populations
production increases in proportion with muscle mass, physical activity, dietary meat consumption, and better overall health status

16. Cystatin C
filtered freely at the glomerulus, but metabolized in the proximal tubules
clearance cannot be calculated.
The primary advantage that its generation appears to be more uniform across populations.
It is not a product of muscle mass
produced by all nucleated cells and released constitutively to the bloodstream.
level may be biased as a marker of kidney function
patients with rapid cell turnover
uncontrolled thyroid disease
corticosteroid use

17. CKD Reclassification by Cystatin C in the REGARDS Cohort
compared the association of reduced eGFR (60mL/min/1.73 m2) defined by creatinine level (using the 2009 CKD Epidemiology Collaboration [CKDEPI] equation) and/or cystatin C (calculated with the 2008 CKD-EPI equation without demographic coefficients) with longitudinal risk of all-cause mortality or ESRD.

18. The
26,643 participants were categorized into 4 mutually
exclusive groups: CKD by both eGFRcr and eGFRcys,
eGFRcr only, eGFRcys only, or neither. Of 2,904
participants with eGFRcr 60 mL/min/1.73 m2, 29%
(n 849) had eGFRcys 60 mL/min/1.73 m2. Compared
with persons with preserved eGFR by both
measures, the group with reduced eGFRcr only had no
significant increase for mortality or ESRD (Table 1).
Conversely, 5% (n 1,378) of the cohort had reduced
eGFRcys only; these persons had a 2-fold mortality
risk and nearly 6-fold ESRD risk compared with the
reference group. Persons with reduced eGFR by both
markers (8%; n2,055) had a 2-fold adjusted mortality
risk, but a 26-fold risk of ESRD compared with the
reference group. The addition of cystatin C level
significantly improved classification of CKD as a
determinant of both outcomes, with net reclassific

19. The impact of this study is that it demonstrated that eGFRcys improves CKD definition and risk stratification relative to eGFRcr as determined by longitudinal risks for 2 major complications of CKD.

20. New CKD-EPI Equations That Incorporate Cystatin C
the CKD-EPI collaborators combined patient-level data from 13 cohorts that used several methodologies to measure GFR
The investigators used a newly established international reference standard for cystatin C to develop new GFR estimating equations.
This standardization overcomes a major limitation of prior cystatin C literature because cystatin C concentrations may have varied by manufacturer and been susceptible to drift

21. The 2012 CKD-EPI cystatin C
equation did not require a race coefficient and
included smaller coefficients for age and sex compared
with the 2009 CKD-EPI creatinine equation.
The 2012 CKD-EPI creatinine–cystatin C equation
also was presented and included creatinine level,
cystatin C level, age, sex, and race (Box 1).

22. The contribution of this study is that it offers state-of-the-art cystatin C equations that are based on the cystatin C reference standard
The combined creatinine–cystatin C equation appears to be the optimal GFR estimate, whereas the 2012 CKD-EPI cystatin C equation has the advantage of not requiring a coefficient for black race, which is a unique attribute among the CKD-EPI equations

23. GFR Estimating Equations in Elders: the Berlin Initiative Study
A major finding
of this study was that cystatin C had a much stronger
association with GFR than creatinine (Fig 2). The
addition of age and sex to creatinine level greatly
improved GFR prediction, but age and sex added little
value to cystatin C level. In this elderly cohort, the
best GFR estimation was derived from a combined
creatinine–cystatin C equation that was developed by
the investigators; however, a cystatin C–only equation
was clearly superior to a creatinine-only equation.

24. Impact- this study of community based elderly persons demonstrated the superiority of cystatin C level relative to creatinine level for GFR prediction.

25. 2012 KDIGO GUIDELINE FOR EVALUATION AND MANAGEMENT OF CKD

26. 2012 KDIGO GUIDELINE FOR EVALUATION AND MANAGEMENT OF CKD

27. 2012 KDIGO GUIDELINE FOR EVALUATION AND MANAGEMENT OF CKD

28. 2012 KDIGO GUIDELINE FOR EVALUATION AND MANAGEMENT OF CKD

30. CKD SCREENING USING CYSTATIN C
Costeffectiveness?
KDIGO guidelines have only endorsed its use for improving the specificity of CKD diagnosis, rather than the sensitivity of CKD detection
3 potential strategies for cystatin C screening:
persons with borderline eGFRcr,
persons at high risk of CKD, and
persons with conditions known to make creatinine level insensitive for detecting CKD (eg, unpredictable muscle mass).

31. THANK YOU