Centrifugation improves detection of HIV-1 p24 antigen in sera from children born to HIV infected mothers.

MARIA NOÉ GARCIA; MARIA SOL DOS RAMOS FARÍAS; ROBERTO DANIEL RABINOVICH; MARIA MERCEDES AVILA

Ciudad de Mexico, Mexico

Conferencia; XVII International AIDS Conference; 2008

International AIDS Society

Introduction: Virus detection is necessary for diagnosis in children born to HIV infected mothers; PCR is the gold standard. p24 antigen (p24) plasmatic detection is a simple economical alternative though less sensitive. The aim of this study was to improve sensitivity of p24 detection using plasma centrifugation. Methods: 65 samples from 55 children (23 infected, 14 uninfected, 18 with a unique-sample-PCR-positive) with a median age of 137 days were retrospectively used. Samples from 33 infected adults were also included. Stored plasmas were defrosted, p24 determination was carried out and remaining plasma volume (0.3-1ml) was centrifuged at 23,500g at 4ºC, 60 minutes. p24 was determined in the resuspended pellet (0,15ml) using Murex HIV antigen Mab, Abbott. Results: out of 32 plasma samples from 23 infected pediatric patients, p24 was positive in 6 (18.7%) plasmas and 24 (75%) pellets. p24 was undetectable in all plasmas and pellets from uninfected children. Specificity was 100% in plasma and pellet. Sensitivity was significantly higher (p=0.001) in pellet. In 18 samples from patients with one-positive-PCR, p24 was detected in 1 plasma (5.5%) while, it was positive in 9/18 pellets. Ratio absorbance/cut-off was always higher in pellet than in plasma (median 23.5, IQR 10.9- 35.5 versus median 2.5, IQR 1.16-9.6;p=0.028). When the pellet was originated from the highest available plasma volume, antigen detection in pellet was more frequent (94.4%vs50%, p=0.006). In samples from adults p24 was detected in 5/33 plasmas (15.15%) and in 9/33 (27.27%) pellets. Conclusions: Results show the benefit of centrifugation prior to p24 determination in pediatric patients since sensitivity augmented from less than 20% to 75% without causing loss of detection in any case. Two phenomena may be involved in p24 increased detection: concentration of particulated antigen and elimination of antibodies or other soluble factors present in plasma that might interfere with p24 detection.