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  • Author: Andries J. Bakker x
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Monoclonal gammopathy is characterized by the presence of an M-protein in serum or urine that has homogeneous structural and functional properties. It can occur in very high concentrations and may cause significant interference in clinical chemistry assays. Examples of gammopathy interference for the analytes glucose, bilirubin, γ-glutamyltransferase, urea and ferritin are presented. Various mechanisms of interference are described, such as the production of turbidity by the M-protein and the binding of the M-protein to a component of the test system or analyte. In immunoglobulin tests, the M-protein is the analyte itself and may not be completely bound by the test antibody owing to its structural properties. Modern analyzers can detect unusual changes in absorption during the course of a reaction, and thus the formation of turbidity due to M-proteins. This interference may be prevented by optimizing the buffering conditions of the reagents to avoid the formation of turbidity or by removal of the M-protein prior to analysis of the sample. Owing to the unique properties of each M-protein, it is impossible to protect common clinical chemistry test systems completely from gammopathy interference. Therefore, efficient ways for the detection of such interference are needed.

Clin Chem Lab Med 2007;45:1240–3.


Background: Detection and quantification of monoclonal proteins is hampered when the monoclonal peak coincides with one of the regular bands in serum proteinelectrophoresis. The objective of this study was to evaluate four procedures for serum proteinelectrophoresis with respect to detection and quantification of monoclonal proteins.

Methods: For 466 patient samples with a monoclonal protein, three variants of agarose gel electrophoresis (5-band, split-β and high resolution) and one variant of capillary electrophoresis were compared with the results of the routinely used agarose gel electrophoresis followed by immunofixation analysis using specific or pentavalent antisera.

Results: In total, 310 patient samples were analyzed by the four methods, consisting of 295 samples with a monoclonal protein, seven with oligoclonal bands and eight without any bands. Suspicion of a monoclonal protein was raised in 295/256/256/232/265 of the samples using the reference/5-band/split-β/high resolution/capillary procedure. In 152/147/135/142/126 of the samples the concentration of monoclonal protein was >1.0 g/L and in 51/33/53/33/67 of the cases, the monoclonal protein was not separated from one of the normal protein zones.

Conclusions: In high resolution agarose gel electrophoresis, monoclonal bands of low concentration often remain undetected. In split-β agarose gel electrophoresis as well as capillary electrophoresis monoclonal bands more often were not separated from the regular protein bands.


Background: The objective of this study was to elucidate the most practical and effective laboratory measurement for monitoring citrate in critically ill patients undergoing citrate-anticoagulated continuous venovenous haemofiltration (CVVH).

Methods: This observational study was performed at the mixed medical and surgical intensive care unit of a regional teaching hospital. The study population comprised ten consecutive critically ill patients with acute renal failure and indication for haemofiltration with the use of regional anticoagulation with citrate. Serum samples for the measurement of citrate and total and ionised calcium were taken from the pre- and post-filter compartments and from the arterial circulation of patients during citrate-anticoagulated CVVH.

Results: Receiver operating characteristic (ROC) curve analysis showed that for detecting citrate overdose (defined as a citrate concentration >1.0mmol/L) the best cut-off limits for total/ionised calcium and ionised calcium were 2.1 and 0.8mmol/L, respectively. Sensitivity and specificity for the cut-off limit of 2.1 for total/ionised calcium were 89% and 100%, and 84% and 100%, respectively, for the cut-off limit of 0.8mmol/L for ionised calcium.

Conclusions: In patients without liver insufficiency, total/ionised calcium performed slightly better than ionised calcium in detecting elevated citrate concentrations. However, because of the simplicity of its measurement, ionised calcium is preferred. Measurement of citrate is not necessary.

Clin Chem Lab Med 2006;44:962–6.


Background: This study evaluates HbA1c measurements from dried blood spots collected on filter paper and compares HbA1c from filter paper (capillary blood) with HbA1c measured in venous blood.

Methods: Patient satisfaction was evaluated using a questionnaire. The performance with the filter paper method was assessed by comparing HbA1c results from EDTA-blood samples obtained via dried blood spots with HbA1c results obtained with freshly hemolyzed blood (routine HbA1c). Adult patients visiting the outpatient clinic for HbA1c analyses were recruited for the evaluation of dried blood spot sampling at home. Laboratory personnel collected a capillary blood sample on filter paper as well as a venous EDTA-blood sample. The participants collected another capillary blood sample at home and sent the dried filter paper back to the laboratory. Samples were analyzed with an immunoturbidimetric assay.

Results: Between-filter coefficient of variation was 1.8%. Filter paper HbA1c increased slightly during storage, particularly during the first 5 days. Filter paper HbA1c highly correlated with routine HbA1c (r=0.987). The evaluation of samples collected at home showed comparable HbA1c values by filter paper and routine sampling methods (n=93). Eighty-three percent of participants said they would like the filter method to be brought into practice.

Conclusions: Home HbA1c sampling on filter paper is an acceptable sampling alternative for analysis of HbA1c.

Clin Chem Lab Med 2009;47:1259–64.


Background: Determination of the length of sedimentation reaction in blood (LSRB) is frequently used in daily practice to assess disease intensity. Recently, a micro-sedimentation method was introduced (TEST 1™) that uses EDTA anti-coagulated blood samples. The aim of this study was to characterize this method by comparing it to a conventional Westergren method (Sedimatic 100). Furthermore, correlation between fibrinogen and the LSRB and the influence of M-proteins on the LSRB was investigated.

Methods: Unselected paired samples were used for comparison between the TEST 1 and Sedimatic 100 methods (n=733); fibrinogen was measured in EDTA samples (n=765) using a turbidimetric method. Furthermore, LSRB was measured in 29 EDTA samples in paired serum tubes from patients in whom an M-protein was detected.

Results: TEST 1 showed excellent correlation with the Sedimatic 100 method (y=1.00x; n=733; r=0.92, 95% CI 0.90–0.93; p<0.0001), and had no significant bias (0.15mm/h, 95% CI –0.48 to 0.75mm/h). Furthermore, TEST 1 LSRB showed satisfactory correlation with the fibrinogen content (y=3.13+0.06x; n=765; r=0.78, 95% CI 0.75–0.80; p<0.0001). In samples containing M-proteins, satisfactory correlation between the M-protein content and TEST 1 LSRB was found (y=0.69+0.22x; n=29; r=0.71, 95% CI 0.45–0.85; p<0.0001), while excellent correlation was found when only M-proteins of the IgM type were taken into account (y=–0.95+0.23x; n=9; r=0.93, 95% CI 0.71–0.99; p<0.0002).

Conclusions: The results confirm previous reports that TEST 1 is a reliable method to measure the LSRB, and shows for the first time the quantitative relationship between TEST 1 LSRB and M-proteins, particularly those of the IgM type.

Clin Chem Lab Med 2006;44:904–6.


Background: The objective of this study was to evaluate the efficiency of free light chain (FLC) analysis in comparison to serum protein electrophoresis (SPE) for detecting M-proteinemia.

Methods: A total of 553 consecutive patients for whom evaluation of M-proteinemia was requested were included in this study. For all patients, serum FLC analysis and SPE followed by pentavalent immunofixation analysis was performed. Identification of monoclonal bands was performed using specific antisera. FLC analysis was performed using the Modular P analyzer in accordance with the manufacturer's recommendations. Local reference ranges for FLCs on this platform were established based on samples from patients with a normal electrophoretic pattern [no monoclonal bands, no hypo- or hypergammaglobulinemia, no acute phase pattern and normal kidney function, i.e., estimated glomerular filtration rate (eGFR) >60 mL/min].

Results: Local reference ranges (95%) were established (n=243): κ: 8.01–28.26 mg/L; λ: 8.07–23.58 mg/L and κ/λ ratio: 0.74–1.66. Negative and positive predictive values were 98.6% and 49.5%, respectively, for screening for M-proteinemia by SPE alone, 94.3% and 21.7% for FLC concentration and 95.1% and 21.4% for FLC with the κ/λ-ratio included. Combining protein electrophoresis and FLCs resulted in a negative predictive value of 99.0% and a positive predictive value of 23.4%.

Conclusions: Serum FLC analysis alone is not suitable for screening for M-proteinemia.

Clin Chem Lab Med 2009;47:1507–11.


Proper sample handling is important for the accurate and prompt diagnosis of cryoglobulinaemia as well as for obtaining correct results of other laboratory tests. In this case report, we present two patients for whom improper sampling delayed the diagnosis of cryoglobulinaemia. The routine sampling procedure was not sufficient for detecting these cryoglobulins and we demonstrated that the temperature dropped below 37 °C at different steps during the sample preparation. Adjusting the pre-analytical procedure revealed that both patients possessed a cryoglobulin with high thermal insolubility. We conclude that in cryoglobulinaemia strict adherence to guidelines to keep the temperature >37 °C is crucial for sample collection and must be strongly recommended.