White Blood Cell Cystine

Clinical Use

Use

This test provides quantitative analysis of cystine in white blood cells. Pathogenic variants in the CTNS gene are associated with cystinosis, a genetic disorder marked by the accumulation of cystine in cells. Nephropathic cystinosis, the most severe form of the disorder, manifests in early childhood with symptoms like renal Fanconi syndrome, which if untreated, may lead to kidney failure. Symptoms including visual impairment, muscle degradation, diabetes, and thyroid issues arise as the disorder progresses. Intermediate cystinosis presents similar symptoms but typically begins in early adulthood, while ocular cystinosis is characterized by light sensitivity without renal complications. Testing is crucial for patients with clinical suspicion of cystinosis and for monitoring those diagnosed with it.

Special Instructions

WBC cystine levels are sensitive to how samples are handled and can decrease quickly. It's crucial that whole blood arrives in the laboratory within 36 hours of drawing. This test should not be shipped for Sunday delivery. An optimized protocol for cystine determination was implemented on March 12, 2013, minimizing loss during preparation. The normal cystine range remains unaffected by this change, however, reported cystine levels for cystinosis patients may appear elevated, possibly leading to concerns regarding patient compliance.

Limitations

This test is sensitive to sample handling; improper conditions may alter results. The protocol change may result in increased cystine levels reported for cystinosis patients, potentially causing confusion regarding treatment adherence. It is critical to adhere to specified shipping conditions to ensure sample integrity and accurate results.

Test Details

New York Approved

Methodology

Mass Spectrometry

Biomarkers

2 components

Primary ComponentCystine Analysis

Result Turnaround Time

8 days

Specimen

Whole Blood (Unknown)

Volume

5-10 ml (adults, children >2 years); 3-5 ml (children <2 years)

Minimum Volume

3 ml

Container

ACD (yellow-top) tube

Collection Instructions

Draw blood in ACD (yellow-top) tubes.

Storage Instructions

Ship at room temperature in an insulated container by overnight courier to arrive within 36 hours of collection. To help maintain the integrity of the sample, shipping with a freezer gel pack is recommended. Do not heat or freeze.