The effect of paraproteins and rheumatoid factor on four commercial immunoassays for vancomycin: implications for laboratorians and other health care professionals.

BACKGROUND: Paraproteins, immunoglobulins (Igs), which are elevated in various autoimmune disorders, are known to interfere with various laboratory immunoassays, including vancomycin (VANC). Rheumatoid factor (RF), a known immunoassay interferant, may cause falsely elevated results. OBJECTIVES: The aims of this study were to (1) evaluate the effect of 3 paraproteins (IgA, IgG, and IgM) on 4 commercial VANC immunoassays [fluorescence polarization immunoassay; enzyme multiplied immunoassay; 2 particle-enhanced turbidimetric inhibition immunoassays]; (2) determine the concentration at which the effect is obtained, and (3) examine the influence of RF on the VANC methods. METHOD: Serum and plasma pools from patients prescribed VANC and a spiked VANC pool (20 mg/L) were each mixed 1:1 with individual patient specimens containing IgA (6-63 g/L), IgG (6-54 g/L), IgM (3-30 g/L) (n = 4 for each Ig), and a patient RF pool (196 IU/L). The mixtures (n = 39) were split and distributed for VANC analysis. RESULTS: IgA and IgG in serum and plasma did not affect any of the VANC immunoassays. RF added to plasma specimens did not interfere, but in serum, elevated VAN results were observed. IgM did not affect the fluorescence polarization immunoassay and enzyme multiplied immunoassay methods but did attenuate VANC concentrations by both particle-enhanced turbidimetric inhibition immunoassays (Siemens, Beckman Coulter), with a more pronounced effect on the latter, producing concentrations >20% lower than expected in the patient serum and spiked plasma pools. The effect was progressively negative at effective IgM concentrations of 10 and 15 mg/L. CONCLUSIONS: This phenomenon is a major analytical and clinical issue that must be communicated to health care professionals caring for patients receiving VANC, so optimal therapy is achieved.

Biochemistry testing associated with pregnancy and the newborn period -- a lot has changed since you were a baby!

Everyone has been a newborn, and everyone's mother has been pregnant. Despite the commonality of these events, medical care and the clinical chemistry laboratory's role in it have changed remarkably over the last 50 years. This review is a historical overview of clinical chemistry testing that is related to pregnancy and the newborn period.

Comparison of lactate, bilirubin and hemoglobin F concentrations obtained by the ABL 700 series blood gas analyzers with laboratory methods.

OBJECTIVE: To compare lactate, bilirubin and Hemoglobin F concentrations obtained on ABL 700 series blood gas analyzers with those from laboratory methods. DESIGN AND METHOD: Pooled neonatal plasma, cord blood and adult plasma samples were used for comparison of bilirubin, hemoglobin F and lactate concentrations respectively. RESULTS: Results obtained on the ABL 700 series compared favorably (Deming regression slopes 0.97-1.13) with those from laboratory methods. For lactate ABL (y) = 1.13 Vitros (x) -0.43 with a CI (slope) of 1.10 to 1.16, CI (int) of -0.61 to -0.28. For hemoglobin F ABL(y) = 1.11 Variant (x) -8.0 with a CI (slope) of 0.88 to 1.33, CI (int) of -25.3 to 9.3. The three bilirubin comparisons are as follows: 1) Unistat (y) = 1.10 Vitros (x) -16.12 with CI (slope) of 1.06 to 1.14 and CI (int) of -25.3 to -6.9. 2), ABL (y) = 0.97 Vitros(x) -10.16 with CI (slope) of 0.94 to 1.00 and CI (int) of -17.6 to 2.73) Unistat (y) = 1.14 (x)-4.58 with CI (slope) of 1.09 to 1.18 and CI (int) of -13.6 to 4.5. CONCLUSION: The ABL 700 series gave comparable results for lactate, bilirubin and hemoglobin F with laboratory methods and may be used in patient care.