The calculator in question is the ACR (American College of Rheumatology) Classification Criteria for Lupus Nephritis. This scoring system is specifically designed for patients with systemic lupus erythematosus (SLE), a chronic autoimmune disease. The calculator is used to classify the severity of lupus nephritis, a serious complication of SLE that affects the kidneys.

The clinical utility of this calculator is to guide treatment decisions and to provide prognostic information. It helps clinicians to stratify patients based on the severity of their kidney disease, which can range from mild to severe. The ACR criteria can also be used in research settings to standardize the definition of lupus nephritis across studies.

There are no specific exclusion criteria for the use of the ACR Classification Criteria for Lupus Nephritis. However, it should be noted that this calculator is not designed to diagnose lupus nephritis. It is intended to be used in patients who have already been diagnosed with SLE and are suspected to have kidney involvement. The diagnosis of lupus nephritis should be confirmed by kidney biopsy.

ACR classification criteria for lupus nephritis

# Criteria
 A. Diagnosis of systemic lupus erythematosus
B. Urine 24-hour protein excretion > 0.5 g/day or urine protein/creatinine ratio > 0.5 mg/mg
C. Urinary cellular casts of > 5 cells per high-power field in the absence of concomitant urinary infection

# Conditions
- A and (B or C)
- true