Cystatin-C is a protein produced by all nucleated cells and filtered out of the bloodstream by healthy kidneys. It is a more sensitive marker of kidney function than creatinine, as its levels rise earlier when glomerular filtration rate decreases. Measurement of cystatin-C can help detect chronic kidney disease at an earlier stage than creatinine. The document discusses the history, molecular biology, structure, role in medicine, prevalence, and stages of chronic kidney disease, highlighting how cystatin-C can be a useful marker for detecting and monitoring kidney function and disease.

1. CYSTATIN-C
Presented by
Dr.Brijesh Mukherjee
P.G.,Biochemistry.

2. HISTORY
• It was first described as “gamma trace in 1961
as a trace protein together with other
ones(such as beta trace) in CSF and in urine of
patient with renal failure.
• Grubb and Lofberg first reported its amino
acid sequencence
• They noticed it was increased in patient of CRF
• It was first proposed as a measure of GFR by
Grubb and co-workers in 1985

3. MOLECULAR BIOLOGY
• Cystatin superfamilly encompasses protein that contain
multiple cystatin like sequences
• Some members are active cysteine proteinase
inhibitors
• There are 3 inhibitory families in the superfamily-
• 1) Type 1 cystatins(stefins)
• 2) Type 2 cystatins
• 3)Kininogens
• Type 2 are a class of cysteine proteinase inhibitors
found in human fluids and are protective in function

4. MOLECULAR BIOLOGY(CONT.)
• They are located in short arm of chromosome
20 which contain majority of type 2 cystatin
genes and pseudogenes
• Highest level found in semen followed by
breast milk,tears and saliva

5. SOME FACTS ABOUT CYSTATIN-C
• Cystatin-c is a non glycosylated basic protein(isoelectric pH 9.3)
• It has a crystal stucture characterized by short alpha helix and a
long alpha helix running across a large antiparallel 5 stranded beta
sheet
• It has 2 disulfide bonds
• 50% of the molecule carry a hydroxylated proline
• It forms two dimers(molecule pairs)
• In human all cells with nucleus produce cystatin c as a chain of 120
amino acids
• It is a potent inhibitor of lysosomal proteinases
• It is also an important inhibitor of extracellular cysteine proteases
• It has a low molecular weight of 13.3 kilodaltons
•

6. SRUCTURE OF CYSTATIN C

7. DIMERS
In biochemistry a dimer is a macromolecular complex formed by two, usually covalently
bound, macromolecules like proteins or nucleic acids. It is a quaternary structure of a protein.

8. ROLE IN MEDICINE
• KIDNEY FUNCTION
• It is removed from bloodstream by
glomerular filtration by kidneys
• if the function of kidneys decrease and GFR
falls, level of cystatin-c in blood increases
• So it has been suggested that cystatin-c
might predict the development of CRF

9. ROLE IN MEDICINE (CONT.)
• Levels of cystatin-c are altered in following conditions
• 1)Cancer patient
• 2)Thyroid dysfunction
• 3)Glucocorticoid therapy
• 4)Cigarette smoking
• 5)HIV infection
• 6)Increased levels in MI,stroke,heart failure,peripheral
arterial syndrome
• 7)Increased in metabolic syndrome
• 8)Increased in alzheimers disease
• 9)Levels decreased in atheroslerosis and
aneurysmal(saccular bulging) lesions of aorta

11. STAGES OF KIDNEY DISEASE
NORMAL Healthy kidney GFR >90 ml/min
STAGE 1 Kidney damage with GFR >90 ml/min
normal/elevated GFR
STAGE 2 Kidney damage with mild GFR 60-89 ml/min
decrease in GFR
STAGE 3 Kidney damage with moderate GFR 30-59 ml/min
decrease in GFR
STAGE 4 Kidney damage with severe GFR 16-29 ml/min
decrease in GFR
STAGE 5 Kidney failure(end stage renal GFR <15 ml/min
disease,ESRD)

12. PREVALANCE

13. METABOLIC EFFECTS IN CRD
Stage (Renal dysfunction) GFR Metabolic Consequences
(ml/min/1.73 m2)
Normal renal function – Persons >90
at increased risk or with early renal
damage
Mild renal insufficiency (ERI) 60-89* PTH levels start to rise (GFR ~ 60-80)
Moderate renal insufficiency (CRI) 30-59 Decrease in Calcium absorption (GFR
<50)
Lipoprotein activity falls.
Malnutrition.
Onset of LVH.
Severe renal insufficiency (Pre-ESRD) 15-29 Triglyceride levels start to rise.
Onset of Anemia (EPO deficiency).
Hyperphosphatemia.
Metabolic acidosis.
Hyperkalemia tendency.
ESRD (Uremia) <15 Azotemia develops.

14. PROGRESSION OF C.R.D.

15. CRITERIA FOR C.R.D.

16. G.F.R.
• GFR is a measure of rate at which water and
dissolved substances(low molecular weight
ultrafiltrable compounds) are filtered out of
blood per unit time through kidneys
• NORMAL GFR
• Males-150 ml/min
• Females-130 ml/min
• Serum creatinine is most common marker
used to measure GFR

17. LIMITATIONS OF CREATININE AS A
MARKER OF GFR
• NON RENAL FACTORS-
• 1.Gender
• 2.Ethinicity
• 3.Diet
• 4.Muscle mass
• 5.Drugs affecting tubular secretion of creatinine
• CLINICAL FACTOR-
• Poor sensitivity for CKD- Creatinine blind range
• Creatinine remains normal until 50% renal function is lost
• Insensitive to loss of GFR in Stage-2 and Stage-3 in CKD
• ANALYTICAL FACTOR-
• Non specific bias frequently reported with Jaffe Assay Method

18. ADVANTAGE OF CYSTATIN-C AS GFR
MARKER
ADVANTAGE COMMENT
Virtually unaffected by non renal factors Muscle mass/weight/height,age(>1 year)-
cystatin-c parallels age related decrease in GFR
and can be used in children
Sensitive to so called creatinine blind range Enables early detection and treatment of CKD
Can be used to detect and monitor kidney Creatinine for GFR in liver disease not
diseases in patient with hepatic diseases recommended
Correlates to appearance of microalbuminuria Clinical studies suggest that very early renal
failure may be the first clinical indication of
progressive renal damage associated with
diabetis

19. CONTRAINDICATION OF CYSTATIN-C
ESTIMATION
• THYROID FUNCTION
• Levels of cystatin-c are sensitive to change in
thyroid function and should not be performed
without knowledge of patients thyroid status
• CORTICOSTEROIDS
• Cystatin-c concentrations are affected in
patients of impaired renal function receiving
corticosteroids

20. LABORATORY MEASUREMENT
• ASSAY PRINCIPLE-
• Cystatin-c in the sample binds to the specific anticystatin-c antibody
which is coated on latex particles and causes agglutination
• The degree of turbidity caused by agglutination is measured
optically and is proportional to the amount of cystatin-c in the
sample by a method called TURBIDIMETRY.
• REFERENCE VALUE-
• Males-0.52-0.98 mg/dl
• Female-0.52-0.90 mg/dl
• Normal value decreases until first year of life,then remains stable
before increasing after age of 50 years
• NOTE-
• Cystatin-c can be measured from a random sample of blood from
which RBC and clotting factors have been removed(i.e. serum)

21. TURBIDIMETRY
• Some analytical methods give an insoluble
product in finely divided form so that the
particles remain in suspension
• If a beam of light passes through,some of it is
scattered-TYNDALL EFFECT
• Turbidimetry measures the reduction of intensity
of the incident beam and is similar to the study of
light absorption in spectrophotometry
• Turbidimetric measurements are done with usual
types of photometers

22. TURBIDIMETRY COMPONENTS

23. TURBIDIMETRY AND NEPHELOMETRY

24. TURBIDIMETER

25. STANDARD GRAPH OF TURBIDIMETRY

26. % INCREASE IN CYSTATIN-C LEVELS
AFTER 50 YEARS

27. SENTITIVITY AND SPECIFICITY OF
CYSTATIN-C/CREATININE

28. GRAPH OF CYSTATIN-C(STD.)

29. GRAPH OF CYSTATIN C ASSAY

30. CYSTATIN-C CONC. VS OPTICAL
DENSITY GRAPH

31. GENTIAN CYSTATIN-C GFR
CALCULATOR
• The calculator gives instant conversion of
cystatin-c measurement to standard GFR units

32. GFR CALCULATOR
CYSTATIN-C(mg/dl) GFR(ml/min)
0.5 217
0.6 167
0.7 133
0.8 110
0.9 93
1.0 80
1.1 70
1.2 61
1.3 55
1.4 49
1.5 45
1.6 41
1.7 37
1.8 34

33. 1.9 32
2.0 29
3.0 16
3.5 13
4.0 11
4.5 09
5.0 08
5.5 07
6.0 06
6.5 05
7.0 05
7.5 04

34. CONCLUSION
• The prevalence of chronic renal diseases are
increasing in INDIA especially with an increase
in cases of diabetis
• Hence it is important to diagnose renal
disease at an early stage to decrease
morbidity and mortality
• The use of CYSTATIN-C as a marker of CRD can
be an important tool to monitor renal disease.

35. THANK YOU