Efficacy of Cyto-Chex blood preservative for delayed manual CD4 testing using Dynal T4 Quant CD4 test among HIV-infected persons in Zambia.

BACKGROUND

Manual CD4 tests such as Dynal T4 Quant (Dynabeads, Dynal Biotech, Oslo, Norway) are less expensive alternatives to flow cytometry in resource-limited countries. Whereas blood preservatives have proven useful for stabilizing blood samples to allow delayed CD4 testing by flow cytometry, they have not been verified for manual tests. A method for preservation of blood prior to manual CD4 testing is needed for long-distance transport or sample batching.

METHODS

Blood from HIV-positive Zambian military beneficiaries was mixed (1:1) with Cyto-Chex (Streck Laboratories, La Vista, NE) blood preservative, and the blood was stored at refrigerated, ambient, and incubator (37 degrees C) temperatures prior to Dynabeads CD4 testing at 0, 3, 6, and 9 days after collection. Baseline flow cytometry and Dynabeads testing without preservative were performed for comparison.

RESULTS

Twenty-seven patient samples were analyzed. Dynabeads vs. flow cytometry had a correlation coefficient (r) of 0.84. There was excellent correlation (r = 0.96) between baseline Dynabeads testing and Cyto-Chex-preserved samples. Refrigerated samples showed strong correlation with baseline Dynabeads (r = 0.93-0.95) on days 3, 6, and 9 without decline in CD4 count (P = 0.73). Samples stored at ambient temperature yielded inferior results (r = 0.76-0.81), with a significant decline in CD4 count by day 3 (P < 0.001). The incubator arm had especially poor correlation (r = 0.30-0.49).

CONCLUSIONS

Addition of Cyto-Chex to peripheral blood (1:1) adequately preserves refrigerated blood samples for up to 9 days for subsequent testing with Dynabeads CD4 test. Cyto-Chex, however, cannot be recommended for delayed Dynabeads CD4 testing with storage at 37 degrees C or ambient temperatures in tropical areas similar to the site of this study.