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This study evaluated serum kappa and lambda free light chain (FLC) concentrations in a Veterans Affairs (VA) population. We hypothesized that our older, mostly male, population should not differ in serum FLC ranges from levels previously established for younger male and female populations and that the assay would improve our screening protocol for plasma cell dyscrasias (PCD). Serum kappa and lambdaFLC were assayed in 312 consecutive serum samples collected during a 16-week period from veterans whose clinical presentation indicated a need for serum protein electrophoresis (SPEP) analysis. We reviewed our laboratory information system (LIS) files to evaluate the patients' diagnoses and treatment status in conjunction with serum FLC levels. All assays and validation studies were conducted using an immunoturbidimetric method with a Roche/Hitachi 911 modular analytical system. The intra-assay variability (CV) was <5%, based on 13 replicate assays of 4 control samples and 1 blank sample. Of the 312 patients, the SPEP results were normal in 235 and abnormal in 77. Of the 235 patients with normal SPEP results, 37 had abnormal FLC values and 20 of these were diagnosed as PCD. Of the 77 patients with abnormal SPEP results, only 9 had diagnoses unrelated to PCD. Using the FLC assay in conjunction with retrospective reviews of medical records, we obtained an 86% detection rate of PCD. This detection rate increased to 100% when both SPEP and FLC results were considered. In conclusion, this study documents an important role for serum FLC assays in diagnosing and monitoring PCD in a VA population. Our results support previously established serum FLC reference ranges that were obtained in younger, male and female populations. Using the serum FLC results in conjunction with SPEP results improves the sensitivity and specificity for managing VA patients whose clinical presentation indicates the need to evaluate PCD.

The purpose of this study was to validate the Albumin Cobalt Binding (ACB) assay at the Seattle Veterans Affairs (VA) Hospital to determine if it would provide an earlier rule-out of acute coronary syndrome (ACS) in patients, compared to current use of cardiac injury markers. This study compares the distribution of ischemia modified albumin (IMA) values of our patient population to those provided by the kit manufacturer. IMA values were determined photometrically on a Roche Modular Analytical System on 200 subjects: 69 subjects not experiencing chest pain (normals), 78 subjects presenting to the emergency room (ER) with chest pain whose initial and subsequent troponin results were negative (non-converters), and 53 subjects presenting to the ER with chest pain whose initial troponin result was negative but subsequent troponin results were positive (converters). Based on the relationships between IMA values in the initial samples from the non-converters and converters, we constructed a ROC curve to identify an optimum IMA rule-out value. The IMA values (mean+/-SD) for the normals, non-converters, and converters were 89+/-7.1, 100+/-13.9, and 126+/-14.1 U/ml, respectively, and each mean was statistically different from the means of the other groups. The ROC curve comparing converters and non-converters showed an area of 0.89 (p <0.001) compared to the line of identity. An IMA cut-off of 97 U/ml gives a 98% sensitivity and 45% specificity and may be the best decision point to differentiate between these groups in our population. Nine of 78 non-converters were classified as having unstable angina. In conclusion, the ACB assay has a strong negative predictive value and sensitivity in our population for predicting the troponin results at 6 to 24 hr post-presentation. Because ACB results may be facility- and instrument-dependent, each facility should conduct an independent ROC analysis to determine the optimal IMA rule-out level. The ACB assay, when used in conjunction with cardiac injury markers and assessment of unstable angina, holds promise in reducing inappropriate low-risk hospital admissions and improving the clinical management of patients with chest pain.

Children with juvenile-onset multiple carboxylase deficiency lack biotinidase activity (biotinamide amidohydrolase, EC 3.5.1.12) in the liver and other tissues. Hence, little free biotin is metabolically available, resulting in seizures, acidosis, and serious neurological damage. As the absence of hepatic biotinidase activity is reflected in serum, assessment of biotinidase status can easily be made from a blood sample. A convenient qualitative procedure for screening infants has been employed in order to estimate serum levels of biotinidase in as little as 10 microliters of sample. This colorimetric procedure detects the formation of free p-aminobenzoate cleaved from the substrate, N-biotinyl-p-aminobenzoate at pH 6.0. The assay is easily performed and has a low incidence of false positive results. A kinetic assay for serum biotinidase has also been developed using biotinyl-p-nitroanilide (BpNA) as substrate. When 50 microliters of biotinidase positive serum was incubated with 0.2 mM BpNA in phosphate buffer at pH 6.0, an increase in absorbance was observed at 405 nm. The rate of change in absorbance was followed kinetically on the Roche Cobas BIO analyzer at 37 degrees C. Monitoring the increase in absorbance of para-nitroanilide every 60 seconds over 30 minutes demonstrated linearity from 10 to 30 minutes. In comparing results from this kinetic assay on 48 randomly selected sera with those obtained using a colorimetric procedure, a correlation coefficient of 0.85 was obtained. Several false positive results were observed in clearly lipemic sera.

Screening programs for late-onset, biotin-responsive, multiple carboxylase deficiency (LMCD) detect colormetrically the presence of biotinidase activity in dried samples of whole-blood spotted on filter-papers as used in the neonatal screening of phenylketonuria. A sensitive and stable qualitative technique is described using 10 microliter of serum that avoids problems associated with poor sample collection, improper drying of blood-spots and transient color development. The modified assay is timely and suitable for the clinical laboratory not involved in mass screening programs.

The serum fructosamine concentrations measured in 64 diabetic patients correlated (r = 0.73) with glycated hemoglobins (HbA1c). However, 23 percent of the diabetic patients had normal fructosamine and abnormal HbA1c levels. In order to determine whether or not the discrepant values were the result of recent glycemic regulation by the diabetic patient, fructosamine levels of patients suffering from diabetic ketoacidosis (along with beta-hydroxybutyrate levels) were closely monitored. It was shown that short term alterations (one to three days) in serum glucose did not significantly affect fructosamine levels. Therefore, disagreements between fructosamine and HbA1c are most likely due to longer term improvement in glucose control by the diabetic or the result of the higher imprecision of the HbA1c assay.