The Italian quality control study for evaluation of CD4 cells in centres involved in the treatment of HIV-1 patients. Italian CD4 Quality Control Group

Abstract

We report on the experience of establishing a national network for a quality control programme in evaluating CD4 cell counts in most Italian centres involved in the care of patients with HIV disease. The 68 centres were divided according to their geographical location into eight groups, and twice a year (tests A and B) they received three coded whole blood samples (two were replicates of the same sample) obtained from two informed HIV+ patients, one with CD4 counts/mm3 expected to be < 200 and one with values > 300. The medians of the determinations performed by the labs involved in each of the eight areas were taken as the 'true' values for each sample. Unsatisfactory performances for percentage of CD4 cells were identified as a CD4 analysis with residual values > or = +/- 5% and with deviates > or = +/- 2. For absolute numbers of CD4 cells, an unsatisfactory performance was defined as CD4 counts with residual > +/- 100 CD4 cells/mm3 and with deviates > or = +/- 2. The residual value is the CD4 value reported by each lab minus the median value. The deviate is the residual divided by the modified interquartile range (IQR x 0.75). Most of the centres provided reliable results. However, some labs failed to provide satisfactory results for percentages (6.25% of the tested labs for test A and 6.17% for test B) or absolute numbers (16.25% test A and 12.34% test B). Only 3.7% of the labs gave unsatisfactory results in both tests. Four of the unsatisfactory results from the two tests gave an error in absolute numbers > +/- 200 CD4 cells/mm3. Our data suggest that most Italian labs provide reliable results in evaluating the numbers of CD4 cells in HIV-1+ samples, but the importance of running a quality control programme is highlighted by our experience with those centres which provide unsatisfactory data which may lead to incorrect classification of the patients or assessment of treatment.

Fig. 1

Test A: sample with expected > 300 CD4/mm³. Results obtained by individual laboratories in each area coordinated by a reference centre (BA, Bari; BO, Bologna; CA, Cagliari; FI, Florence; GE, Genoa; MI1 and 2, Milan 1 and Milan 2; PD, Padoa; RM, Rome). (a) Percentage of CD4 cells. The 0 line represents the ‘true’ value, calculated as the median of all the determinations performed in each area. Individual results are expressed as percentage residuals according to 1993 NIH Guidelines for flow cytometry. Residual values ≥ ± 5% and with deviates ≥ ± 2 are considered as unsatisfactory (in this case the deviate value is reported in the Figure). Median percentage values were: 19 (BA), 24 (BO), 23 (CA), 18 (FI), 20 (GE), 20 (MI1), 29 (MI2), 33 (PD), 39 (RM). (b) Absolute numbers of CD4 cells. The 0 line represents the ‘true’ value, calculated as the median of the determinations performed in each area. Individual results are expressed as residual values. An unsatisfactory level of performance was defined as CD4 counts with residual values > ± 100 CD4 cells/mm³ and with deviates ≥ 2 (in this case the deviate value is reported in the Figure). Median absolute values were: 331 (BA), 551 (BO), 481 (CA), 480 (FI), 608 (GE), 309 (MI1), 649 (MI2), 509 (PD), 729 (RM).

Fig. 2

Test A: sample with expected < 200 CD4/mm³. Results obtained by individual laboratories in each area coordinated by a reference centre. Results are summarized as reported in Fig. 1. (a) Percent of CD4 cells. Median percentage values were: 7 (BA), 9 (BO), 11 (CA), 21 (FI), 15 (GE), 8 (MI1), 11 (MI2), 19 (PD), 19 (RM). (b) Absolute numbers of CD4 cells. Median absolute values were: 156 (BA), 176 (BO), 211 (CA), 389 (FI), 170 (GE), 143 (MI1), 125 (MI2), 267 (PD), 220 (RM).

Fig. 3

Test B: sample with expected > 300 CD4/mm³. Results obtained by individual laboratories in each area coordinated by a reference centre. Results are summarized as reported in Fig. 1. (a) Percent of CD4 cells. Median percentage values were: 36 (BA), 22 (BO), 19 (FI), 21 (GE), 14 (MI1), 30 (MI2), 27 (PD), 30 (RM). (b) Absolute numbers of CD4 cells. Median absolute values were: 624 (BA), 346 (BO), 408 (FI), 258 (GE), 323 (MI1), 416 (MI2), 370 (PD), 673 (RM).

Fig. 4

Test B: sample with expected < 200 CD4/mm³. Results obtained by individual laboratories in each area coordinated by a reference centre. Results are summarized as reported in Fig. 1. (a) Percent of CD4 cells. Median percentage values were: 17 (BA), 22 (BO), 5 (FI), 16 (GE), 10 (MI1), 9 (MI2), 8 (PD), 7 (RM). (b) Absolute numbers of CD4 cells. Median absolute values were: 224 (BA), 177 (BO), 36 (FI), 60 (GE), 104 (MI1), 103 (MI2), 154 (PD), 125 (RM).