• 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
• 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
• Cystatin C is a small 13 kDa protein (most potent inhibitor of
• Constant production rate, regulated via house-keeping gene
• Not influenced by muscle mass , or inflammation
• Free renal filtration
• No tubular secretion
• Tubular reabsorption followed by degradation.
• The family 3 Cystatins, high and low molecular weight
kininogen, contain three Cystatin domains and are mainly
intravascular proteins, which in addition to being inhibitors of
cysteine proteases also are involved in the coagulation
process and in the production of vasoactive peptides.
• Cystatin C is abundant in various tissues and bodily fluids,
the highest levels having been determined in cerebrospinal
fluid, seminal fluid, plasma, and synovial fluid.
• Half life (N-END RULE).
• Protein with N-Terminal Met,Ser,Thy,Val, or Gly.
Have half life more than 20 hours.
• Protein with N-Terminal Phe,Leu,Asp,Lys, or Arg.
Half life of 3 minutes or less.
• PEST: Proteins with Pro(P),Glu (E),Serine (S)
Thr(T) are more rapidly degraded.
• Papain is well studied plant (CP).
• Cathepsins are large family of lysosomal cysteine
• Caspase are involved in activation & implementation
• Calpains are Ca++ activated cysteine proteases that
cleave intracellular proteins.
• They regulate processes such as cell migration and
• Sereine proteases.
• Cysteine proteases.
• Aspartyl proteases.
• Metal ion proteases (Zn++)
• Threonine proteases.
• *Best substrate is unfolded proteins.
• The human Cystatin family presently comprises 11 identified
• Two of these, Cystatin A and B, form the family 1 Cystatin
and are mainly, or exclusively, intracellular proteins, while
Cystatin C, D, E, F, S, SA and SN are mainly extracellular
and/or transcellular proteins and constitute the family 2
• The family 3 cystatins are mainly intravascular proteins,
produces vasoactive peptide & involved in coagulation.
FATE OF CYSTATIN-C
• Produced by all nucleated cells and its rate of
production is constant.
• In human, all cells with nucleus produce cystatin
C as a chain of 120 amino acids
• It is freely filtered at the Glomerulus.
• Practically completely reabsorbed by proximal
• It is totally catabolized in the proximal renal
• No re-entry into circulation.
FATE OF CYSTATIN C
• Cystatin superfamily encompasses proteins 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
• Type 2 are a class of cysteine proteinase inhibitors found in
human fluids and are protective in function
SOME FACTS ABOUT CYSTATIN-C
• Cystatin-C is a non glycosylated basic protein (isoelectric pH 9.3)
• It has a crystal structure characterized by short alpha helix and a
long alpha helix running across a large anti-parallel 5 stranded beta
• It has 2 disulfide bonds
• 50% of the molecule carry a hydroxylated proline
• It forms two dimers
• 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
Types of cystatin
• The human cystatin family presently comprises of 11 identified
• FAMILY 1: Two cystatin A and B, and are mainly, or exclusively,
• FAMILY 2: C, D, E, F, S, SA and SN are mainly extracellular
and/or transcellular proteins and constitute the family 2 Cystatins.
• Family 3 cystatins: high and low molecular weight kininogen,
contain three cystatin domain & are mainly intravascular proteins.
• In addition to inhibitors of cysteine protease also involved in
CALCULATION OF GFR
• CKD-EPI cystatin equation adjusted for age,
sex and race:
• Formula for calculation of eGFR:
• eGFR = 127.7 X (Cys C)-1.17 X (age)-0.13 X
0.91 (if female) X 1.06 (if African American)
CALCULATION OF GFR
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
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 atherosclerosis and aneurysmal(saccular bulging)
lesions of aorta
• A reliable marker of GFR in patients with mild-to-moderate
kidney dysfunction (stages 2–3 of CKD) in both type 1 and
type 2 diabetes.
• Elevated serum cystatin C levels identified as a significant
prognostic indicator for the development of cardiovascular
disease in people with diabetes.
• Cystatin C is not only a better indicator of GFR in diabetes, it
has the best correlation with changes in GFR over two
years, making it a useful measure for follow-up of patients
VIRUS (HIV) INFECTION
• Studies have reported increased cystatin C
levels in HIV.
• Because of an increase of cystatin C levels
with active HIV infection, an overestimation of
kidney impairment may occur, particularly in
treatment-naive patients with renal disease.
• Like creatinine concentrations, cystatin C
levels are also lower in the hypothyroid and
higher in the hyperthyroid state as compared
with the euthyroid state.
• Cystatin C has been reported to be a potent predictor
of cardiovascular mortality beyond classical risk factors
in patients with CAD and normal or mildly reduced
• Serum cystatin C may have a stronger association
with mortality and cardiovascular disease than
serum creatinine in patients without CKD, as
reported in a large study of older adults.
• Serum cystatin C concentrations are increased in human
obesity in relation to over-production by the adipose tissue.
So, cystatin C levels are higher in obese subjects as
compared to lean.
• Adipose tissue is a source of cystatin C in a way that is not
related to eGFR but to the status of adipose tissue itself,
including enlarged adipocytes, hypoxia, pro-inflammatory
cytokines production, increased number of macrophages,
and probably other cellular and molecular alterations known
to occur in obesity
METHODS FOR GFR ESTIMATION
GFR measurement Creatinine Cystatin C
( reference method)
- 125 I-iothalamate
not routinely USED
• time & labor intensive
- invasive, stress-full
•Small molecule, 113
( breakdown product
of creatine as part of
• Routine clinical
- Jaffe method
•different formulas for
eGFR, e.g. MDRD
• Small protein, 13
• Fully automated
• HIGHLY SENSITIVE
• SPECIFIC MARKER
• CHRONIC KIDNEY DISEASE
• ACUTE RENAL FAILURE
• CARDIOVASCULAR EVENTS
• ALL CAUSE MORTALITY
• HEART FAILURE
• UNSUCCESSFUL AGING
CKD – a silent threat
Kidneys do not hurt!
• Laboratory testing = key to early diagnosis
• Prevention as more efficient as earlier
• Sensitive detection method required
• Continuous strong increase in the prevalence
of chronic kidney disease
CKD – a silent threat
CKD – a silent threat
• Outcomes of CKD:
- progression of renal disease to end-stage renal
• Complications of CKD:
- bone and mineral disease
- increased risk of cardiovascular disease
• GFR declines with age and cystatin C may
better reflect true kidney function in older
people because muscle mass does not
• After age 50, reference values of serum
cystatin C concentration are higher.
• Serum cystatin C concentration varies in
pregnancy, because it is not consistently
• In preeclampsia, however, altered kidney
function is more likely to be detected by CysC–
GFR than by creatinine-based formulas.
• After age 1, serum cystatin C concentration is
constant, but higher values are found in the
newborn period. In full-term newborns, cystatin C
progressively declines over the first week of life.
• CysC–GFR has been reported to be more accurate
in children with cancer and in patients with spina
LIMITATIONS OF CREATININE AS A MARKER OF GFR
• NON RENAL FACTORS-
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
ADVANTAGE OF CYSTATIN-C AS GFR MARKER
Virtually unaffected by non
year)-cystatin-c parallels age
related decrease in GFR and
can be used in children
Sensitive to so called creatinine
Enables early detection and
treatment of CKD
Can be used to detect and
monitor kidney diseases in
patient with hepatic diseases
Creatinine for GFR in liver
disease not recommended
Correlates to appearance of
Clinical studies suggest that
very early renal failure may be
the first clinical indication of
progressive renal damage
associated with diabetes
CONTRAINDICATION OF CYSTATIN-C
• THYROID FUNCTION
• Levels of cystatin-C are sensitive to change in
thyroid function and should not be performed
without knowledge of patients thyroid status
• Cystatin-C concentrations are affected in
patients of impaired renal function receiving
• 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
• REFERENCE VALUE-
– Males-0.52-0.98 mg/dl
• Normal value decreases until first year of life,then remains stable before increasing
after age of 50 years
– Cystatin-c can be measured from a random sample of blood from which RBC
and clotting factors have been removed(i.e. serum)
• 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-
• Turbidimetry measures the reduction of intensity of the
incident beam and is similar to the study of light absorption
• Turbidimetric measurements are done with usual types of