Twenty-four-hour Bence-Jones protein determinations: can we ensure accuracy?

CONTEXT

Light chain disease represents 15% to 20% of cases of multiple myeloma. Current guidelines recommend monitoring these patients with 24-hour urine collections.

OBJECTIVE

To determine the reliability of 24-hour urine collections in assessing the amount of Bence-Jones protein (BJP).

DESIGN

We included all patients from our institution from 2003 through 2008 with BJP who had more than four 24-hour urine collections. We compared BJP excretion calculated from the submitted 24-hour collection with BJP excretion calculated by normalizing the collection to that patient's mean 24-hour creatinine excretion. We also looked at differences in serial values with these 2 methods. In addition, we evaluated the feasibility of using random urine samples to determine BJP excretion.

RESULTS

A total of 14 patients with 135 24-hour urine collections met our inclusion criteria. The 24-hour urine creatinine excretion for each patient, which should be reasonably constant, varied considerably (coefficient of variation range 12%-30%). Differences in the 2 methods of calculating BJP excretion ranged from -1588 to 2315 mg/d. Among a total of 121 serial 24-hour measurements, the differences were clinically significant in 37 (30%). Among a total of 23 random urine samples from 11 of these patients submitted within 10 days of a 24-hour collection, the estimated BJP excretion appeared to be accurate in at least 18 (78%).

CONCLUSIONS

Twenty-four-hour urine collections for BJP are, in practice, often misleading. At a minimum, one should verify that the 24-hour creatinine excretion is accurate. In addition, it may be possible to use the protein/creatinine ratio from random urine samples to determine 24-hour BJP excretion.