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Phenx toolkit Supplemental Information Domain: Diabetes Release Date: 10/1/2015 Cystatin c assay for Kidney Function


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PhenX Toolkit Supplemental Information

Domain: Diabetes

Release Date: 10/1/2015

Cystatin C Assay for Kidney Function





About the Measure

Domain

Diabetes

Measure

Cystatin C Assay for Kidney Function

Definition

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




About the Protocol

Description of Protocol

This protocol provides instructions for drawing, processing and storing blood for the serum cystatin C assay according to the National Health and Nutrition Examination Survey (NHANES) methods. As there are no standard assays for cystatin C, the protocol also provides basic guidelines to aid comparability among different studies.
The Diabetes Working Group recommends that the cystatin C assay can be done in conjunction with serum creatinine to yield more information about kidney disease (Levey, 2014)

Note from the Diabetes Working Group: The investigator should record the reason a sample person is excluded from the blood draw.

Note from the Diabetes Working Group: Blood should be collected in an appropriate 5- or 10-mL red-top tube.
Note from the Diabetes Working Group: The Diabetes Working Group recommends that the investigator record whether the blood was drawn and whether the full amount was obtained.
Note from the Diabetes Working Group: 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 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 also 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. While 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, while 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 assuring 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 utilized to estimate glomerular filtration rates (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 potential 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.



Protocol text

The following is a summary version of the full National Health and Nutrition Examination Survey 2007-2008 protocol.
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 SP answer “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 SP answer “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:

http://www.cdc.gov/nchs/data/nhanes/nhanes_07_08/manual_lab.pdf


  • 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 Groups 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]
Stevens, LA, Coresh, J, Schmid, CH, Feldman, HI, Froissart, M, Kusek, J, Rossert, J, Van Lente, F, Bruce, RD, Zhang, Y, Greene, T, & Levey, AS. (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.

Participant

Participant 6 years of age or older.

Source

Centers for Disease Control and Prevention (CDC). National Center for Health Statistics (NCHS). National Health and Nutrition Examination Survey Questionnaire. Laboratory Procedures Manual. Hyattsville, MD: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, 2007.

Language of Source

English

Personnel and Training Required

Phlebotomist

Laboratory that can perform the cystatin c assay



Equipment Needs

Phlebotomy supplies

Protocol Type

Bioassay

General References

Inker LA, Okparavero A. (2011) Cystatin C as a marker of glomerular filtration rate: prospects and limitations. Curr Opin Nephrol Hypertens. 20(6):631-639


Levey AS, Inker LA, Coresh J. (2014) GFR estimation: from physiology to public health. Am J Kidney Dis. 63(5):820-834
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.
Stevens, LA, Coresh, J, Schmid, CH, Feldman, HI, Froissart, M, Kusek, J, Rossert, J, Van Lente, F, Bruce, RD, Zhang, Y, Greene, T, & Levey, AS. (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.



Process and Review

The Expert Review Panel #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)








PhenX Toolkit Supplemental Information

Cystatin C Assay for Kidney Function



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