Protocol - Cystatin C Assay for Kidney Function

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Protocol Name from Source:

National Health and Nutrition Examination Survey (NHANES) Questionnaire. Laboratory Procedures Manual


Publicly available


This protocol provides instructions for drawing, processing, and storing blood for the serum cystatin C assay according to the NHANES methods. Because there are no standard assays for cystatin C, the protocol also provides basic guidelines to aid comparability among different studies.


Exclusion Criteria

Persons will be excluded from this component if they:

Report that they have hemophilia; or

Report that they have received cancer chemotherapy in the last 4 weeks

SP = Sample Person.

1. Do you have hemophilia?

[ ] 1 Yes

[ ] 2 No

[ ] 7 Refused

[ ] 9 Don't Know

If the SP answers "Yes," the SP is excluded from the blood draw.

If the SP answers "No" or "Don't Know," blood is drawn from the SP.

2. Have you received cancer chemotherapy in the past four weeks or do you anticipate such therapy in the next four weeks?

[ ] 1 Yes

[ ] 2 No

[ ] 7 Refused

[ ] 9 Don't Know

If the SP answers "Yes," the SP is excluded from the blood draw.

If the SP answers "No" or "Don't Know," blood is drawn from the SP.

Venipuncture Procedures

Editor's Note: Please review chapter 4 of the Laboratory Procedures Manual from the National Health and Nutrition Examination Survey for a full description of Phlebotomy procedures: http://www.cdc.gov/nchs/data/nhanes/nhanes_07_08/manual_lab.pdf

Venipuncture should generally be performed using the median cubital, cephalic, or basilic veins in the left arm unless this arm is unsuitable. If the veins in the left arm are unsuitable, look for suitable veins on the right arm. If the veins in the antecubital space on both arms are not suitable, then look for veins in the forearm or dorsal side of the hand on the left arm/hand and then the right arm/hand.

Record the Results of the Venipuncture Procedure

Immediately after completing the venipuncture, record the results of the blood draw, the reasons for a tube not being drawn according to the protocol, and any comments about the venipuncture.

Process the Sample for the Cystatin C Assay

Editor's Note: Please review chapter 8 of the Laboratory Procedures Manual from the National Health and Nutrition Examination Survey 2007-2008 for a full description of Blood Processing procedures:


Allow the blood to clot by setting aside for 30 to 45 minutes at room temperature. Do not clot for more than an hour.

Centrifuge the tube at room temperature to separate the serum and aliquot into an appropriate storage tube.

Determine if the serum is hemolyzed, turbid, lipemic, or icteric. If so, enter a comment to describe the plasma.

Laboratory Assay for Cystatin C

The Diabetes Working Group notes that although there is not a standardized assay, there are many different kits which are appropriate to measure the concentration of cystatin C in serum. Once an assay is chosen for a particular study, the Working Group recommends that no changes in the protocol be made over the course of the study.

Reference Ranges

Cystatin C ranges between 0.57 - 1.12 mg/L

Estimated Glomerular Filtration Rate:

estimated Glomerular Filtration Rate = 127.7 X Cystatin C -1.17 X Age -0.13 X [0.91 if Female] X [1.06 if African American]

Personnel and Training Required


Laboratory that can perform the cystatin C assay.

Equipment Needs

Phlebotomy supplies


Requirement CategoryRequired
Average time of greater than 15 minutes in an unaffected individualNo
Major equipmentNo
Specialized requirements for biospecimen collectionNo
Specialized trainingNo

Mode of Administration

Life Stage:

Child, Adolescent, Adult, Senior, Pregnancy

Specific Instructions:

Lipemic or frozen specimens, which become turbid after thawing, may interfere with the assay (Mayo Clinic, n.d.).

Note from the Diabetes Working Group: The Diabetes Working Group recommends that the cystatin C assay be done in conjunction with serum creatinine to yield more information about kidney disease (Levey, et al 2014)

The investigator should record the reason a sample person is excluded from the blood draw. Blood should be collected in an appropriate 5- or 10-mL red-top tube. The Diabetes Working Group recommends that the investigator record whether the blood was drawn and whether the full amount was obtained. Serum should be stored at -80°C until testing and shipped on dry ice to prevent thawing. To aid comparability, the Diabetes Working Group recommends that the investigator record the make and manufacturer of equipment used and the repeatability and coefficients of variation for the assay.

Note from the Diabetes Expert Review Panel: Plasma or serum

collection of blood samples for the measurement of analytes requires a general determination of whether to use serum or plasma for the assay and a determination of the type of collection tube to be obtained. For example, if serum is to be used, a determination needs to be made as to whether red top or serum gel separator collection tubes are used. Although comparable values are obtained for many analytes from either serum or plasma, there may be situations where differences are more pronounced and serum- or plasma-specific norms will be needed for references. The protocol presented here uses red top/serum separator tubes. At times, it may be possible to collect both, but other considerations, such as participant burden, may be the deciding factor. It is important to match assay type with sample type. Some automated devices may preclude the use of serum, for example, whereas others may be optimized for it. Investigators should choose methods of collection that match the methods of analysis. This will best be done by communicating with the laboratory where the proposed assays will be performed. They will become an important partner with you in ensuring that there is compatibility from collection, to assays, to interpretation and reporting of levels and results.

Note from the Sickle Cell Disease Research and Scientific Panel:

The Sickle Cell Disease Research and Scientific Panel acknowledges that the serum cystatin C values have been used to estimate GFR in individuals with sickle cell disease. However, cystatin C values have not been validated in this population using actual determination of GFR. Results from the BABY HUG Trial suggest that cystatin C values underestimate true GFR. Because inflammation, gender, ethnicity, and other factors may affect cystatin C levels, caution should also be used when interpreting cystatin C results from eGFR equations until these formulas have been validated in SCD.

The serum concentration of cystatin C remains unchanged with infections and with inflammatory or neoplastic states, and it is not affected by body mass, diet, or drugs. Thus, cystatin C may be a more reliable marker of renal function (GFR) than creatinine (Mayo Clinic, n.d.).

Research Domain Information

Release Date:

July 2, 2018


A bioassay to measure serum concentration of cystatin C, a protein that is filtered out of the blood by the kidneys.


Cystatin C is a protein produced by the body. Cystatin C measurements can indicate kidney function problems and assess kidney disease. For the elderly, those who are overweight, and people who have a lot of muscle mass (e.g., body builders), Cystatin C-based estimates for glomerular filtration rate (eGFR) are believed to be less influenced by muscle mass or diet than creatinine-based estimates (National Kidney Foundation, 2015).This measurement of renal function is particularly important to old people with reduced muscle mass, which makes other assays less accurate.

Selection Rationale

The National Health and Nutrition Examination Survey, produced by the Centers for Disease Control and Prevention's (CDC's) National Center for Health Statistics (NCHS), is one of the most widely used national surveys and was selected as the best practice methodology.





Process and Review

The [link[phenx.org/Default.aspx?tabid=872|Expert Review Panel (ERP) #1]] reviewed the measures in the Anthropometrics, Diabetes, Physical Activity and Physical Fitness, and Nutrition and Dietary Supplements domains.

Guidance from the ERP includes:

  • Added recommendations on use of serum or plasma

    Previous version in Toolkit archive ([link[www.phenxtoolkit.org/index.php?pageLink=browse.archive.protocols&id=140000|link]]).


Centers for Disease Control and Prevention (CDC), National Center for Health Statistics (NCHS), National Health and Nutrition Examination Survey Questionnaire, Laboratory Procedures Manual, 2007.

General References

Inker, L. A., & Okparavero, A. (2011) Cystatin C as a  marker of glomerular filtration rate: prospects and limitations. Current Opinion in Nephrology and Hypertension, 20(6), 631-639

Levey, A. S., Inker, L. A., & Coresh J. (2014) GFR estimation: From physiology to public health. American Journal of Kidney Diseases, 63(5), 820-834

Mayo Clinic. (n.d.). Test ID: CYSTC: Cystatin C with Estimated GFR, Serum. Retrieved from https://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/35038.

Miles, R. R., Roberts, R. F., Putnam, A. R., & Roberts, W. L. (2004). Comparison of serum and heparinized plasma samples for measurement of chemistry analytes [Letter to the Editor]. Clinical Chemistry, 50(9), 1704-1705.

National Kidney Foundation. (2015). A to Z Health Guide: Cystatin C. Retrieved from https://www.kidney.org/atoz/content/cystatinC.

Stevens, L. A., Coresh, J., Schmid, C. H., Feldman, H. I., Froissart, M., Kusek, J., ... Levey, A. S. (2008). Estimating GFR using serum cystatin c alone and in combination with serum creatinine: A pooled analysis of 3,418 individuals with CKD. American Journal of Kidney Diseases, 51(3), 395-406.

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