Role of urine and serum protein electrophoresis in evaluation of nephrotic-range proteinuria.

The usefulness of routine serum protein electrophoresis (SPEP) and urine protein electrophoresis (UPEP) screening in the evaluation of proteinuria is not known. The data on the clinical utility of these tests in 165 male patients with proteinuria greater than 3 g/d of protein who were screened for the presence of an M-spike are presented. Two hundred fifty-four studies were performed (SPEP, 155; UPEP 99) in these 165 patients. Twenty-four studies (9.8%) were positive for an M-spike (15 serum; 9 urine samples) in 19 patients (11.5%). Fourteen patients (8.5%) had an M-spike in either serum or urine, five patients (3%) in both studies. Two of these 19 patients were diagnosed with myeloma and 1 patient was diagnosed with primary amyloidosis. The other 16 patients were diagnosed with monoclonal gammopathy of unknown significance (MGUS). The group with a positive M-spike was significantly older (mean +/- SEM, 65 +/- 2 years; range, 39 to 78 years v 58 +/- 1 years; range, 25 to 84 years; P = 0.03), had a lower incidence of coexistent diabetes (21.1% v 61.6%; P = 0. 01), and a lower serum albumin level (3.2 v 3.6 g/dL; P = 0.05). Using a multivariable logistic regression model, the presence of an M band was positively correlated with age (odds ratio [OR], 1.056; 95% confidence interval [CI], 1.006 to 1.108) and negatively correlated for serum albumin level (OR, 0.386; 95% CI, 0.184 to 0. 810), hematocrit (OR, 0.923; 95% CI, 0.852 to 1.001), and the presence of diabetes mellitus (OR, 0.128; 95% CI, 0.038 to 0.434). In summary, routine SPEP and UPEP screening in patients with proteinuria greater than 3 g/d of protein detected an M-spike in 11. 5% and myeloma in 1.2% of the patients. The cost per case of myeloma or MGUS discovered was $1,192.

Monitoring of monoclonal gammopathies: rational use of densitometry and rate nephelometry.

The follow-up of patients with monoclonal gammopathies at our institution includes serial serum protein electrophoresis (SPE) with densitometry and IgG, IgA, and IgM quantitative immunoglobulin (QIG) determinations by rate nephelometry. This retrospective audit compares monoclonal protein concentration as estimated by SPE versus QIG in 456 serial serum specimens from 105 patients to determine whether any of the tests provide redundant information. A comparison of the methods demonstrated good correlation between SPE (x-axis) and QIG (y-axis) quantitation for each immunoglobulin class: IgG had a slope of 1.45 and an intercept of 1.60 (Sy/x = 7.46, r = 0.96, n = 250); IgA had a slope of 1.30 and an intercept of -1.37 (Sy/x = 6.85, r = 0.96, n = 78); and IgM had a slope of 1.95 and an intercept of 2.06 (Sy/x = 5.16, r = 0.98, n = 128). The data for individual patients showed similar good correlations. Exceptions included IgA peaks "buried" in the beta region of the SPE (resulting in invalid SPE estimates of monoclonal protein concentration), and IgG peaks of less than 10 g/L (when background polyclonal IgG immunoglobulin skews the QIG estimate of monoclonal protein concentration). An algorithm is proposed whereby monoclonal protein concentration is measured by the specific QIG (i.e., IgG, IgA, or IgM) determination for the routine monitoring of patients, except for those with IgG peaks of less than 10 g/L that are followed by SPE.