Question

Serum cystatin C as a marker of kidney function , its role in diagnosis , prognosis , and detection of renal impairments , in addition include in you reports the pros and cons of cystatin C as a marker of kidney function.

In clinical laboratory testing , how can we minimize pre - analytical , analytical and post - analytical errors ?

please i need a Complete , not brief answer ( detailed )

Answer 1

Serum cystatin C is a non-glycosylated, 13.3-kDa protein belonging to cystatin protease inhibitors. It has shown promise as a replacement for serum creatinine in estimation of GFR.

It is fully catabolized in the proximal renal tubule and is not returned to blood. Concentration of serum cystatin C is not affected by gender, age, race, protein intake, and muscle mass, unlike serum creatinine. When GFR decreases, cystatin C level begins to rise proportionately.

Role in diagnosis,prognosis and detection of renal impairment

Serum cystatin C is elevated much before serum creatinine levels start rising. Serum cystatin C has a higher sensitivity in identifying early kidney dysfunction, which is missed by relying on serum creatinine alone.

Afterglomerular filtrationThe creatinine blind area is the range between 40 and 70 ml/min/1.73 m2where a decrease in GFR starts to occur. Early reduction in GFR will not be shown up with creatinine testing, whereas cystatin C will show a true positive reduction in GFR. The creatinine test will give a false negative result. The cystatin C test will give a true positive. Cystatin C does not have a blind area. Early diagnosis of AKI based on serum cystatin C helps in timely intervention to have favorable outcome. Cystatin C indicates a more real-time functional state of the kidney and without the lag period as in the case with creatinine measurement. Cystatin C-based GFR gives a direct and accurate measurement of GFR independent of age and muscle mass. It is fully

Pros

Cystatin C production in the body is a stable process that is not influenced by renal conditions, increased protein catabolism, or dietetic factors. Moreover, it does not change with age or muscle mass like creatinine does. Its biochemical characteristics allow free filtration in the renal glomerulus, and subsequent metabolism and reabsorption by the proximal tubule. For these reasons, serum cystatin C has been suggested to be an ideal endogenous marker of GFR.

Cons

Association between serum cystatin C and GFR is more complex during pregnancy and in infants and children.

In patients with chronic liver disease, neither serum cystatin C nor creatinine reliably predicts the GFR.

Cystatin C is related to obesity and inflammation and thus its levels may not always represent real renal function

It is highly expensive than creatinine test

CysC may underestimate clearance in transplant patients and that CysC may be increased in cancer patients require additional studies to determine the effect of increased cell turnover/death on values of this protein that is present in every nucleated cell.

Normal serum cystatin C level ranges from 0.6 to 1 mg/l.

Minimize errors by find whether the patient is under corticoid therapy or thyroid diseases or cardiac diseases

Cystatin C: Lipemic or frozen specimens, which become turbid after
thawing, may interfere with the assay.So careful about the specimen to minimise errors
eGFR: eGFR is not a precise measure of GFR and can be influenced
by non-renal factors (eg, inflammation).so value may be errored.