A Challenging Diagnosis of IgG4-Related Disease When Understanding Limitations of Laboratory Testing Was Pivotal

Table 1

IgG subclass analysis for this patient showing varying values at different labs.

Sample date	September 2015		February 2016
Performing lab	Lab A	Lab B	Lab A	Lab C	Reference intervals (g/L)
IgG1 (g/L)	13.8	18	19.1	20.0	3.82–9.29
IgG2 (g/L)	5.64	>10.1	46.13	43.20	2.42–7.00
IgG3 (g/L)	1.36	>2.1	1.01	6.69	0.22–1.76
IgG4 (g/L)	0.734	>3.3	0.309	5.94	0.039–0.864
Calculated total IgG (g/L)	21.5		66. 6	75.8
Reported total IgG by home lab (g/L)	69.5		76.7		6.1–16.2

IgG4 levels were underestimated at Lab A.