Table 5

Quality control studies for SF CPPD

StudyNumber of SF samples examinedNumbers of participating laboratories or observersCPPDComment
2511 SF of which 2 contained CPPD2 Laboratories compared with reference laboratoryOnly 1/4 CPPD crystal SF correctly identified 3 False positivesPoor. One laboratory failed to identify CPPD at all
One false negativeBUT too few test samples
244 SF of which 1 contained CPPD and 1 contained both CPPD and MSUM25 LaboratoriesOnly 6/50 CPPD crystal SF correctly identified!Very poor
CPPD missed or misidentified
2712 SF of which 4 contained CPPD6 Laboratories17/24 CPPD crystal SF correctly identified 4 Laboratories good results (14/16 correct) 2 Laboratories poor, only 50% or less correct, and scored 3 false positives for CPPDVariable
2896 Slide preparations of SF, 42 with synthetic CPPD added1 LaboratoryMean sensitivity 83%Improved with higher concentrations
Concentration ranged from 1 to 1000 μg/ml6 ObserversMean specificity 78%
High false positive result
2911 SF, 3 containing CPPD1 LaboratorySensitivity 56%Good for both Gram stained and wet preparations
Gram stained and wet preparations of each SF3 ObserversSpecificity 96%