Inter- and intra-laboratory variability of CD4 cell counts in Swaziland

Southern African Journal of HIV Medicine

Field Value
Title Inter- and intra-laboratory variability of CD4 cell counts in Swaziland
Creator Mlawanda, Ganizani Rheeder, Paul Miot, Jacqui
Description Background. Analytical variability in CD4 enumeration is well known, but few studies from southern Africa have quantified the inter- and intra-laboratory variability in CD4 count measurements. In addition, the possible impact of time lapse after sample collection on CD4 reliability is not well understood.

Methods. A cross-sectional study was conducted at Royal Swaziland Sugar Corporation Hospital and three laboratories, Lab A (comparator), Lab B (national reference) and Lab C (rural hospital). Blood from HIV-infected individuals was collected using routine venepuncture into separate specimens for each of the three laboratories. The samples were further subdivided at each laboratory: one was run at 12 hours and the second at 24 hours after venepuncture. The results of absolute CD4 count and CD4 percentage testing were compared within (intra-laboratory) and between (inter-laboratory) laboratories.

Results. Among 53 participants, the mean CD4 count at 12 hours was 373 cells/μl, 396 cells/μl and 439 cells/μl, and at 24 hours 359 cells/μl, 389 cells/ μl and 431 cells/μl, for laboratories A, B and C, respectively. The coefficient of intra-laboratory variation was 4%, 8% and 20% for CD4 count for laboratories A, B and C, respectively. Comparing 12- and 24-hour measurements, the mean difference (bias) within the laboratories between the two time points (and limits of agreement, LOAs) was 14 (-46 to 73), 8 (-161 to 177) and 7 (20 to 33) cells/μl for labs A, B and C, respectively. Comparing Lab A versus Lab B, lab A versus Lab C and Lab B versus Lab C, the inter-laboratory bias for the CD4 count at 12 hours was -32, -64 and -38 cells/μl, respectively. The corresponding LOAs were -213 to 150, -183 to 55, and -300 to 224, respectively. At 24 hours, the biases and LOAs were similar to those at 12 hours.

Conclusions. CD4 counts appeared reliable at all three laboratories. Lab B and Lab C were clinically interchangeable with the comparator laboratory, Lab A, but not between themselves. Time to measurement does not affect the interlaboratory agreement within 12 and 24 hours.

S Afr J HIV Med 2012;13(2):59-63.
Publisher AOSIS
Date 2012-06-07
Type info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion —
Format text/html application/pdf
Identifier 10.4102/sajhivmed.v13i2.139
Source Southern African Journal of HIV Medicine; Vol 13, No 2 (2012); 59-63 2078-6751 1608-9693
Language eng
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Rights Copyright (c) 2012 Ganizani Mlawanda, Paul Rheeder, Jacqui Miot