Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (884 page)

   Use

   New marker to estimate GFR independent of gender, age, and muscle mass, and cirrhosis; does not need to be corrected for height or weight. It is superior to serum creatinine.

   Sensitive marker of allograft function (although it may not be an optimal marker in patients receiving glucocorticoids).

   In the assessment of adverse cardiovascular events (CHF, ischemia, death) because kidney dysfunction is associated with such events.

   Interpretation

Increased In

   Glucocorticoid treatment

   May also be affected by thyroid disorders

   Limitations

   Due to immaturity of renal function in neonates, cystatin C levels are higher in those <3 months of age.

   Increased levels can be associated with higher levels of CRP or BMI and steroid use.

   In transplant patients, extrarenal elimination at higher levels and higher intraindividual variation compared to serum creatinine.

CYSTIC FIBROSIS (CF) MUTATION ASSAY
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   Definition

   CF assay identifies mutations in the cystic fibrosis transmembrane conductance regulator (
CFTR
) gene. To date, more than 1,700 mutations have been identified for CF (OMIM# 219700). Current guidelines, revised by the American College of Medical Genetics (ACMG) in 2004, recommend for routine screen-ing a 23-mutation panel. CF screening also may identify the 5T/7T/9T variants in the CFTR gene. Complete analysis of the CFTR gene by DNA sequencing is appropriate for patients with a clinical diagnosis consistent with CF, patients with a family history of CF, males with congenital bilateral absence of the vas deferens, or newborns with a positive newborn screening result when mutation testing, using the standard 23-mutation panel, has a negative result.