Objective: Detection of BK virus associated large T-antigen is crucial for the diagnosis of polyomavirus nephropathy. Method: In an international multi-centre trial we assessed the inter-observer and inter-laboratory variability for BK immunohistochemistry. A tissue microarray was constructed comprising 23 specimens representative of the whole analytical spectrum from negative over mild to strong SV40 positive cases. 81 participants at 60 centers stained the TMA slides using local protocols. Participants evaluated their slides following a provisional Banff grading schema. Details regarding local staining protocols and evaluation scores were collected online. Stained slides were returned for centralized panel re-evaluation. Weighted kappa statistics were used to determine the variability. Results: The BK inter-observer reproducibility was substantial (mean kappa 0.64), but inter-laboratory reproducibility was below chance (kappa −0.22). Separating components of BK evaluation schema into stain intensity and stain percentage showed no significant improvements in reproducibility. However, collapsing the proposed BK scoring schema into a simple positive/negative call improved BK inter-laboratory variability to 0.77. Conclusion: These results indicate a significant variability between laboratories for detecting the SV40 large-T antigen by immunohistochemistry in paraffin sections. Any proposed grading schema for BK nephropathy, which is dependent on percentage and intensity of nuclear staining, will essentially not be reproducible between laboratories. Objective: Cryopyrin-Associated Periodic Syndrome (CAPS) is a rare hereditary inflammatory disorder with three differents phenotypes: familial cold autoinflamatory syndrome, Muckle-Wells syndrome and neonatal-onset multisysten inflamtory disease CAPS results from a mutation of the NLRP3 gene (1q44) coding for cryopyrin, which forms intracellular protein complexes (inflammasomes). Results: Case report: 41 year old women with chronic renal disease stage 3 (creatinin 2,2 mg/dl and proteinuria 180 mg/ 24 h) who developed urticarial episodies since 6 months old related to cold exposure. After 11 years old patient describe associated to these episodios bilateral arthritis (knes, ankles and elbows), conjunctival inflammation, shivers, and asthenia, more frequently in winter and precipitated by cold exposure, air conditioning, stress and menstruatión. Aditionaly the patient developed in last years bilateral hypoacusis A kidney biopsy showed a amorphous, acellular and acidophilic material Congo red positive deposits at interstition, arteries and arterioles and less frequent at glomeruli. This material displays apple green birefringence by polarizad light microscopy. Diagnosis: SECONDARY RENAL AMYLOIDOSIS Conclusion: The clinico-Pathologial findings of this case are compatible with Muckle-Wells syndrome. Secondary amyloidosis is a severe complication which occurs in 25 % of Muckle-Wells cases. Amyloidosis is cause by increase of C-protein and A amyloid during the episodies before described and deposition of the A amyloid in differents tissues.