Reflexed cryptococcal antigenaemia detection rates in the Western Cape, South Africa.

Background: Reflexed cryptococcal antigenaemia (CrAg) testing has been offered on remnant CD4 specimens with a count < 100 cells/µL from 2017 in South Africa. The Western Cape is the only province to introduce CrAg testing for counts of 100 cells/µL to 200 cells/µL.

Objectives: The objective of this study was to assess the reflexed CrAg detection rate in the Western Cape.

Method: The retrospective analysis of laboratory data for reflexed CrAg testing was conducted between September 2022 and May 2024. The CrAg detection rate was reported for the following CD4 categories at the provincial, district, and sub-district levels: (1) < 100 cells/µL, (2) ≥ 100 cells/µL - ≤ 200 cells/µL, and (3) ≤ 200 cells/µL.

Results: Data are reported for 80 809 specimens, with a CrAg detection rate of 4.0% for a CD4 ≤ 200 cells/µL compared to 6.2% for a count < 100 cells/µL. For a count of ≥ 100 cells/µL - ≤ 200 cells/µL, a CrAg detection rate of 2.1% was reported. The district CrAg detection rate for counts ≤ 200 cells/µL ranged from 1.4% (Central Karoo) to 5.9% (Cape Winelands). Excluding subdistricts without CrAg-positive specimens, the detection rate ranged from 1.3% (Beaufort West) to 8.3% (Swartland).

Conclusion: The study findings of a CrAg detection rate of 4.0% in the Western Cape province justifies their decision to extend reflexed screening to a threshold of 200 cells/µL. However, most CrAg-positive specimens were identified for a count < 100 cells/µL. Intensified approaches to find CrAg-positive patients with a count ≤ 200 cells/µL are required.