Lab: Cystatin C Measurement

Jurisdiction: JM Part B. States: North Carolina, South Carolina, Virginia, West Virginia. Type: Active LCD

History/Background and/or general information Cystatin C is a low molecular weight protein produced by all nucleated cells in the body at a constant rate. Cystatin C is freely filtered by the renal glomerulus, completely reabsorbed by the proximal tubule, and then metabolized by the proximal tubule. It has been proposed and investigated as an improved marker of renal function and as a potential alternative to serum creatinine based estimated glomerular filtration rate (e GFR), as well as a biomarker for predicting cardiovascular risk. Clinical assessment of kidney function is part of routine medical care for adults. GFR is the best overall index of kidney function. Normal GFR varies according to age, sex, and body size, and declines with age. Routinely, GFR is estimated from prediction equations, which are based on endogenous serum markers like creatinine, in addition to, demographic variables such as age, sex and race. The National Kidney Foundation recommends using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) Creatinine Equation (2009) to estimate GFR. Cystatin C is considered to be a potential alternative to serum creatinine for estimating GFR. GFR can be estimated (eGFR) from serum cystatin C utilizing an equation which includes the age and sex of the patient. Cystatin C eGFR may have advantages over creatinine eGFR in certain patient groups in whom muscle mass is abnormally high or low (e.g., individuals who are very elderly, malnourished, or have quadriplegia). Serum creatinine levels may also be influenced by diet (e.g., vegetarian or high protein diets) and medications that block distal tubule secretion of creatinine. Blood levels of cystatin C also equilibrate more quickly than creatinine. Therefore, serum cystatin C may be more accurate than serum creatinine when kidney function is rapidly changing (for example amongst hospitalized individuals). Cystatin C levels have been reported to be abnormally elevated or decreased in some medical conditions (e.g., HIV disease and thyroid disease) and by some medications (e.g., corticosteroids). In clinical situations where confirmation of the eGFR by serum cystatin C is warranted, equations that combine serum cystatin C and serum creatinine provide a more precise eGFR than equations using serum cystatin C alone. Estimation of GFR from serum creatinine remains the clinical standard worldwide. Covered Indications Cystatin C testing is medically reasonable and necessary when all of the following are met: In adults with eGFR creat 45–59 ml/min/1.73 m2 (Chronic Kidney Disease (CKD) stage 3A mildly to moderately decreased GFR) who do not have markers of kidney damage; and If confirmation is warranted When GFR estimates based on serum creatinine are thought to be inaccurate; and When decisions depend on a more accurate knowledge of the GFR, such as confirming a diagnosis of CKD, determining eligibility for kidney donation, or adjusting the dosage of toxic drugs that are excreted by the kidneys. Limitations The following are not reasonable and necessary and therefore, will be denied: Measurement of cystatin C to assess cardiovascular risk is considered investigational in the risk assessment and management of cardiovascular disease. Cystatin C is not covered according to Title XVIII of the Social Security Act, §1861(xx)(1). Therefore, cystatin C measurement is considered not medically reasonable and necessary. Based on the Kidney Disease Outcomes Quality Initiative (KDOQI™) US Commentary on the 2012 Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline for the Evaluation and Management of CKD, cystatin C testing is considered not medically reasonable and necessary for patients with following stages of CKD: Stage 1 Kidney damage with normal or elevated GFR > 90 ml/min/1.73 m 2 Stage 2 Kidney damage with mild decrease in GFR 60-89 ml/min/1.73 m 2 Stage 3B Moderately to Severely decreased GFR 30-44 ml/min/1.73 m 2 Stage 4 Severely decreased GFR 15-29 ml/min/1.73 m 2 Stage 5 Kidney Failure GFR 2