Table 4

Quality control studies for MSUM

Study reference	Number of SF samples examined	Numbers of participating laboratories or observers	Results	Comment
25	11 SF of which 7 contained MSUM crystals	2 Laboratories compared with reference laboratory	5/7 MSUM crystal SF were correctly identified by 1 laboratory	Fair
			3/7 MSUM crystal SF were correctly identified by 1 laboratory
			There was one false positive result
			Sensitivity was calculated as 62.5%

24	4 SF of which 1contained MSUM alone, and 1 contained both MSUM and CPPD	25 Laboratories	39/50 MSUM crystal SF correctly identified, 78% Accuracy	Good

27	12 SF of which 4 contained MSUM	6 Laboratories	19/24 MSUM crystal SF correctly identified, 15/16 by 4 laboratories (good)	4 Laboratories good
			But the results for the other 2 laboratories were poor (50% correct and scored 2 false negatives and 3 false positives)	2 Laboratories poor

26	4 SF of which 1 contained MSUM	25 Laboratories	19/25 Laboratories identified MSUM crystal SF correctly. 24% False positives	Good

28	96 slide preparations of SF, 41 with synthetic MSUM added. Concentrations of MSUM 0.1–100 μg/ml	1 Laboratory	Mean sensitivity 69%	MSUM identification improved at higher crystal concentrations
		6 Observers	Mean specificity 93%

29	11 samples, 3 with MSUM Gram stained and wet preparation set up for each sample	1 Laboratory	78% Sensitivity	Results equally good for Gram stained and wet preparations of SF
		3 Observers	100% Specificity