The Banff Working Group Classification of Definitive Polyomavirus Nephropathy is a diagnostic scoring system used specifically in the field of nephrology. This classification system is applied to patients who have undergone kidney transplantation and are suspected of having polyomavirus nephropathy, a serious complication that can lead to graft loss. 

The clinical utility of this calculator is to standardize the diagnosis of polyomavirus nephropathy, which can be challenging due to its variable clinical presentation and histological findings. The Banff classification provides a systematic approach to evaluate the histological features of kidney biopsy specimens, allowing for a more accurate and consistent diagnosis. 

There are no specific exclusion criteria for the use of this classification system. However, it should be noted that it is intended for use in kidney transplant recipients and not in the general population or in patients with native kidney disease. It also requires a kidney biopsy, which may not be feasible or safe in all patients.

Banff Working Group classification of definitive polyomavirus nephropathy

# Criteria
 ## Polyomavirus load score, positive tubules/ducts (pvl score)
A. < 1% (pvl1)
B. 1-10% (pvl2)
C. > 10% (pvl3)
## Banff lesion score for interstitial fibrosis (ci score)
D. 0-5% (ci0)
E. 6-25% (ci1)
F. 26-50% (ci2)
G. > 50% (ci3)

# Conditions
- A and (D or E)
- (A and (F or G)) or (B and (D or E or F or G)) or (C and (D or E))
- C and (F or G)
- true