Test Overview

Test Methodology

Competitive protein binding assay.

Test Usage

The intracellular cystine content of acid-stabilized white blood cells may be used to evaluate the cystine-depleting effect of Cystagon or to diagnose (or rule out) new cystinosis patients. White cells are used because cystine is not elevated in red cells or plasma of cystinosis patients. (It is elevated in urine also, but this is not diagnostic.) The normal value is generally less than 0.2 nmol half cystine/mg white cell protein. The cystinosis value is generally greater than 2 nmol half cystine/mg white cell protein.

Reference Range*

Interpretive report provided.

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Test Details

Days Test Performed

Monday - Thursday

Analytic Time

10 - 14 days

Soft Order Code


MiChart Code

Cystine, Leukocytes (MMGL)



Cystine, Leukocytes
Cystine, Leukocyte
White blood cell cystine
Leukocyte Cystine Shadow
Leukocyte Preparation

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Laboratory Reference

UCSD Cystine Determination Lab

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Specimen Requirements

Offsite Collection Instructions

Contact MLabs Client Services Center prior to collection of specimen for instructions regarding sample preparation or to confirm that UMHS specimen processing tech will be available. Blood must be collected 5-6 hours after a dose of Cystagon and processed immediately for the white cell cystine measurements to be meaningful.

Special Handing

Contact the MMGL laboratory at 734-615-2429 for instructions prior to collection of specimen.
Page 0603 immediately for sample pick-up by laboratory if at the UMHS hospital complex.

Rejection Criteria

Sample not received within required time interval.

Normal Volume

5 mL whole blood

Minimum Volume

3 mL whole blood

Additional Information

Test sent to University of California, San Diego, Department of Pediatrics, Cystine Determination Laboratory.

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