title: Freezing adversely affects measurement of vascular endothelial growth factor levels in human aqueous samples.
abstract: OBJECTIVE
  Aqueous levels of vascular endothelial growth factor (VEGF) can be a surrogate marker of intraocular VEGF activity and a measure of efficacy of anti-VEGF treatment in a variety of vasoproliferative retinal disorders, including diabetic retinopathy, age-related macular degeneration, and central retinal vein occlusion. Measurement of the VEGF level may be adversely affected by premeasurement variables, such as freezing and delay, in sample analysis. We aim to evaluate the effect of storage and delayed measurement of human aqueous VEGF levels in these conditions.
  
  
  METHODS
  Aqueous samples collected from patients receiving intravitreal injection of bevacizumab for various retinal diseases were divided into two groups. In Group 1, the VEGF levels were analyzed on the same day; in Group 2, the VEGF levels were analyzed after 21 days of freezer storage (-80°C) using immunobead assay. Statistical comparison using a paired t-test was performed between the two groups.
  
  
  RESULTS
  Thirty-one aqueous humor samples were collected, and the VEGF concentration for fresh samples was 7.8 ± 5.9 pg/mL (mean ± SD) compared to 6.5 ± 6.0 pg/mL in frozen samples, resulting in a statistically significant difference (P = 0.03).
  
  
  CONCLUSIONS
  Accurate measurement of the VEGF level is a vital component of clinical decision-making. Delayed analysis of VEGF levels in aqueous samples may result in significant sample degradation and lower levels of measured VEGF.
authors.affiliation: Department of Ophthalmology, University of Florida College of Medicine, Jacksonville, FL, USA.
authors.forename: Sankarathi
authors.initials: S
authors.lastname: Balaiya
authors.forename: Sandeep
authors.initials: S
authors.lastname: Grover
authors.forename: Ravi K
authors.initials: RK
authors.lastname: Murthy
authors.forename: Kakarla V
authors.initials: KV
authors.lastname: Chalam