The Bonn Risk Index (BRI) of Laube et al for Estimating the Risk of Calcium Oxalate Crystallization in Urine

Molecular weight of oxalic acid: 90.04 grams

Parameters:

(1) 24 hour urine ionized calcium in mmol/L

(2) 24 hour urine oxalic acid in mmol/L

Bonn risk index =

= (concentration of ionized calcium) / (concentration of oxalic acid)

Interpretation:

• An index > 1 is considered at risk for calcium oxalate stone formation.

• An index <= 1 is low risk for calcium oxalate stone formation.

Limitation:

• The index for healthy patients in the study had a mean value of 1.05 with a range of 0.06 to 4.89. This means that some low risk patients will have an index > 1.

• The patients with calcium oxalate stones had a mean value of 2.87 with a range of 0.278 to 23.

• Because there is some overlap in the populations, it might be useful to have low, moderate and high risk groups.