Amylase in drain fluid for the diagnosis of pancreatic leak in post-pancreatic resection

BACKGROUND

The treatment of people with clinically significant postoperative pancreatic leaks is different from those without clinically significant pancreatic leaks. It is important to know the diagnostic accuracy of drain fluid amylase as a triage test for the detection of clinically significant pancreatic leaks, so that an informed decision can be made as to whether the patient with a suspected pancreatic leak needs further investigations and treatment. There is currently no systematic review of the diagnostic test accuracy of drain fluid amylase for the diagnosis of clinically relevant pancreatic leak.

OBJECTIVES

To determine the diagnostic accuracy of amylase in drain fluid at 48 hours or more for the diagnosis of pancreatic leak in people who had undergone pancreatic resection.

SEARCH METHODS

We searched MEDLINE, Embase, the Science Citation Index Expanded, and the National Institute for Health Research Health Technology Assessment (NIHR HTA) websites up to 20 February 2017. We searched the references of the included studies to identify additional studies. We did not restrict studies based on language or publication status, or whether data were collected prospectively or retrospectively. We also performed a 'related search' and 'citing reference' search in MEDLINE and Embase.

SELECTION CRITERIA

We included all studies that evaluated the diagnostic test accuracy of amylase in the drain fluid at 48 hours or more for the diagnosis of pancreatic leak in people who had undergone pancreatic resection excluding total pancreatectomy. We planned to exclude case-control studies because these studies are prone to bias, but did not find any. At least two authors independently searched and screened the references produced by the search to identify relevant studies.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data from the included studies. The included studies reported drain fluid amylase on different postoperative days and measured at different cut-off levels, so it was not possible to perform a meta-analysis using the bivariate model as planned. We have reported the sensitivity, specificity, post-test probability of a positive and negative drain fluid amylase along with 95% confidence interval (CI) on each of the different postoperative days and measured at different cut-off levels.

MAIN RESULTS

A total of five studies including 868 participants met the inclusion criteria for this review. The five studies included in this review reported the value of drain fluid amylase at different thresholds and different postoperative days. The sensitivities and specificities were variable; the sensitivities ranged between 0.72 and 1.00 while the specificities ranged between 0.73 and 0.99 for different thresholds on different postoperative days. At the median prevalence (pre-test probability) of 15.9%, the post-test probabilities for pancreatic leak ranged between 35.9% and 95.4% for a positive drain fluid amylase test and ranged between 0% and 5.5% for a negative drain fluid amylase test.None of the studies used the reference standard of confirmation by surgery or by a combination of surgery and clinical follow-up, but used the International Study Group on Pancreatic Fistula (ISGPF) grade B and C as the reference standard. The overall methodological quality was unclear or high in all the studies.

AUTHORS' CONCLUSIONS

Because of the paucity of data and methodological deficiencies in the studies, we are uncertain whether drain fluid amylase should be used as a method for testing for pancreatic leak in an unselected population after pancreatic resection; and we judge that the optimal cut-off of drain fluid amylase for making the diagnosis of pancreatic leak is also not clear. Further well-designed diagnostic test accuracy studies with pre-specified index test threshold of drain fluid amylase (at three times more on postoperative day 5 or another suitable pre-specified threshold), appropriate follow-up (for at least six to eight weeks to ensure that there are no pancreatic leaks), and clearly defined reference standards (of surgical, clinical, and radiological confirmation of pancreatic leak) are important to reliably determine the diagnostic accuracy of drain fluid amylase in the diagnosis of pancreatic leak.

Meeting Requirements of the California Cholinesterase Monitoring Program

California (CA) has a long-standing formal blood cholinesterase (ChE) monitoring program for mixers, loaders, and applicators of pesticides. When the authors found commercial clinical kits were not optimal for assaying blood ChEs, CA regulations were revised to specify use of the Ellman ChE assay or to demonstrate a conversion factor with a correlation ( r2) of 0.9 or better. The authors were enlisted to work with the clinical laboratories. Only two of seven participating laboratories generated an acceptable correlation for red blood cells (RBCs), whereas four of five laboratories had an acceptable correlation for plasma ChE. Subsequently, the CA Department of Pesticide Regulation (DPR) restated the need to meet this requirement and the authors worked with several of the clinical laboratories using a bovine ghost RBC ChE as a reference. Unfortunately, only 3 of 10 laboratories had acceptable correlations. Next, the authors provided all interested laboratories with human blood and plasma samples to perform the comparison study outlined in the regulation (Section 6728f). Fourteen laboratories participated; 9 met the ChE criteria for whole blood, 14 for plasma, and 6 for RBCs. Based on such data, on July 8, 2003, DPR notified the CA Agricultural Commissioners that nine of the participating laboratories were approved for ChE testing. Later work resulted in acceptable RBC values for two of the laboratories and their approval. The authors continue to work with laboratories interested in being on the approved list. The current list may be seen at www.cdpr.ca.gov/docs/whs/lablist.htm .

Establishing Reference Intervals of Aspartate Aminotransferase-to-Platelet Ratio Index for Apparently Healthy Elderly

BACKGROUND

Aspartate aminotransferase (AST) to platelet ratio index (APRI) serves as a parameter in evaluating liver fibrosis in current clinical practice. However, reference standard (reference intervals, RIs) or baseline levels of APRI have not been previously reported. The purpose of this paper is to establish the reference intervals of APRI in apparently healthy elderly people from the region of Shuyang, China.

METHODS

Blood specimens were collected from local elderly residents (selected 51,263 elderly Han Shuyang Chinese from 65 to 97 years old, 32.97% males and 67.03% females) by standard procedures. Complete blood counts were determined by Sysmex XE-2100 analyzer and the AST values were measured by a TBA2000FR automatic biochemical analyzer (Toshiba Co., Ltd., Japan). The 95% reference intervals were calculated by using the non-parametric method according to the document: Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Guideline-Third Edition (C28-A3) of CLSI.

RESULTS

RIs established for healthy elderly include: 0.1398-0.6266 for males and 0.1282-0.5798 for females (0.1284-0.5086 for 65-74 years old; 0.1209-0.5704 for > or = 75 years old). Ris of APRI for elderly males were higher than those of females, and values of APRI increased with increasing age for females.

CONCLUSIONS

We established scientific and reasonable RIs of APRI for the healthy elderly in our region.

The Application of Six Sigma Techniques in the Evaluation of Enzyme Measurement Procedures in China

BACKGROUND

Recently, Six Sigma techniques have been adopted by clinical laboratories to evaluate laboratory performance. Measurement procedures in laboratories can be categorized as "excellent", "good", and "improvement needed" based on sigma (σ) metrics of σ ≥ 6, 3 ≤ σ < 6, and σ < 3, respectively. The quality goal index (QGI) was further investigated for measurement procedures with σ ≤ 3. Improvements of the procedures were recommended based on QGI: QGI < 0.8 indicates that the precision of the procedure needs to be improved; QGI > 1.2 indicates that the trueness of the procedure needs to be improved; 0.8 ≤ QGI ≤ 1.2 indicates that both the precision and trueness of the procedure need to be improved.

METHODS

Fresh frozen sera containing seven enzymes (ALT, ALP, AMY, AST, CK, GGT, and LDH) were sent to 78 clinical laboratories in China. The biases for measurement procedures in each laboratory (Bias) were calculated based on the target values assigned by 18 laboratories performing IFCC (International Federation of Clinical Chemistry and Laboratory medicine) recommended reference methods. The imprecision of each measurement procedure was represented by coefficient variations (CV) calculated based on internal quality control (IQC) data. The σ and QGI values were calculated as follows: σ = (TEa-Bias)/CV; QGI = Bias/(1.5 x CV). TEa is allowable total error for each enzyme derived from biological variation.

RESULTS

Our study indicated that 7.9% (6/76, ALP) to 31.0% (18/58, AMY) of the participating laboratories were scored as "excellent" (σ ≥ 6), 21.1% (16/76, ALP) to 41.3% (31/75, CK) of the laboratories were scored as "good" (3 ≤ σ < 6), and 31.0% (18/58, AMY) to 71.1% (54/76, ALP) of the laboratories need to improve their enzyme measurement procedures (σ < 3). For those with σ < 3, QGIs were further calculated. Based on QGI values, 8.6% (5/58, AMY) to 35.9% (28/78, LDH) of the laboratories (QGI < 0.8) need to improve the precision of the procedures, 8.0% (6/75, CK) to 52.6% (40/76, ALP) of the laboratories (QGI ≤ 1.2) need to improve the trueness of the procedures; and 2.7% (2/75, AST) to 16.3% (8/49, GGT) of the laboratories (0.8 ≤ QGI ≤ 1.2) need to improve both the precision and trueness of the procedures.

CONCLUSIONS

Even though rapid progress has been made to standardize serum enzyme measurements in China in recent years, our study using Six Sigma techniques still suggested that approximately 31.1% to 71.0% of the laboratories need to improve their enzyme measurement procedures, either in terms of precision, trueness, or both.

Disease progression in chronic hepatitis C patients with normal alanine aminotransferase levels

AIM: To investigate whether the disease progression of chronic hepatitis C patients with normal alanine aminotransferase (ALT) levels differs by ALT levels.

METHODS: A total of 232 chronic hepatitis C patients with normal ALT (< 40 IU/L) were analyzed. The patients were divided into “high-normal” and “low-normal”ALT groups after determining the best predictive cutoff level associated with disease progression for each gender. The incidence of disease progression, as defined by the occurrence of an increase of ≥ 2 points in the Child-Pugh score, spontaneous bacterial peritonitis, bleeding gastric or esophageal varices, hepatic encephalopathy, the development of hepatocellular carcinoma, or death related to liver disease, were compared between the two groups.

RESULTS: Baseline serum ALT levels were associated with disease progression for both genders. The best predictive cutoff baseline serum ALT level for disease progression was 26 IU/L in males and 23 IU/L in females. The mean annual disease progression rate was 1.2% and 3.9% for male patients with baseline ALT levels ≤ 25 IU/L (low-normal) and > 26 IU/L (high-normal), respectively (P = 0.043), and it was 1.4% and 4.8% for female patients with baseline ALT levels ≤ 22 IU/L (low-normal) and > 23 IU/L (high-normal), respectively (P = 0.023). ALT levels fluctuated during the follow-up period. During the follow-up, more patients with “high-normal” ALT levels at baseline experienced ALT elevation (> 41 IU/L) than did patients with “low-normal” ALT levels at baseline (47.7% vs 27.9%, P = 0.002). The 5 year cumulative incidence of disease progression was significantly lower in patients with persistently “low-normal” ALT levels than “high-normal” ALT levels or those who exhibited an ALT elevation > 41 U/L during the follow-up period (0%, 8.3% and 34.3%, P < 0.001).

CONCLUSION: A “high normal” ALT level in chronic hepatitis C patients was associated with disease progression, suggesting that the currently accepted normal threshold of serum ALT should be lowered.

[The preanalytical stage of under measuring of concentration of catalytic activity of enzymes: the characteristics and tasks of standardization]

The article explains the importance of standardization, the development and maintenance of rules and recommendations regulating the conditions and order of implementation of particular parts of preanalytical stage. The order of these conditions is noted including the rules stated and published in such normative documents as national standards GOST R 15 189-2009, GOST R 53079.4-2008, GOST R ISO 6710-209 and in the recommendations of foreign National societies ofclini-cal chemistry and laboratory medicine. These requirements concern all the analytes, enzymes included. The cited data have a practical significance for acquisition of reliable results in everyday functioning of laboratories. Enough to mention data concerning the anticoagulants influence on catalytic concentration of enzymes, the most often measured concentrations of alpha-amylase, lipase, amynotransferase, alkaline and acid phosphatase, creatine kinase, lactate dehydrogenase, choline esterase, hemolysis impact, the increased concentration of bilirubin and hyperlipemia in samples and significance of measurement of indices of serum and plasma as well. The possible mechanisms of impact of these interferents on the results of measurement of catalytic concentration of enzymes are discussed.

Evaluation of commutability of several materials for harmonization alkaline phosphatase catalytic concentration measurements

BACKGROUND

The International Standard ISO 18153 establish that one of the requirements to assure the metrological traceability of values for catalytic concentration of enzymes is the commutability of calibrator and control materials used in the reference measurement systems. This approach was applied to verify the commutability of several commercial stabilized materials using the recently published alkaline phosphatase IFCC primary reference procedure and two routine procedures.

METHODS

ALP catalytic activity was measured in 50 serum samples and 16 commercial materials, including control materials from EQAS programs, using primary reference measurement procedure and two routine measurement procedures with AMP and DEA as buffers. Calibration materials with a value assigned by reference procedure which were proved to be commutable were used to recalculate the serum values obtained by routine procedures.

RESULTS

All commercial materials showed a similar behaviour to the patient specimens when AMP vs IFCC procedures were compared. For DEA vs IFCC comparison only one calibration material and two quality control materials were commutable. Recalculation of serum results with a commutable common calibrator improves the agreement between methods changing the ratio AMP vs IFCC from 1.44 to 1.04 and DEA vs IFCC from 3.02 to 1.05.

CONCLUSIONS

The use of a common commutable calibration material allows harmonizing ALP measurements and made traceable patient results to reference procedure.

ADAMTS-13 assays in thrombotic thrombocytopenic purpura

ADAMTS-13, the thirteenth member of the ADAMTS (A Disintegrin And Metalloprotease with Thrombo-Spondin 1 repeats) family, is the plasma metalloprotease responsible for regulating the multimeric structure of VWF. In congenital or acquired deficiency it is actively involved in the pathophysiology of thrombotic thrombocytopenic purpura (TTP), a rare but life threatening disease characterized by microangiopathic haemolytic anaemia and consumptive thrombocytopenia leading to disseminated microvascular thrombosis and variable signs and symptoms of organ ischemia and damage. In the last few years, a number of in house and commercial laboratory assays for ADAMTS-13 and its autoantibodies have been developed. The features and clinical utility of ADAMTS-13 assays are summarized in this review.

Assessment of three new parasite lactate dehydrogenase (pan-pLDH) tests for diagnosis of uncomplicated malaria

A study to assess the diagnostic capabilities of three parasite lactate dehydrogenase (pan-pLDH) tests, Vistapan), Carestart and Parabank), was conducted in Uganda. An HRP2 test, Paracheck-Pf), and a Giemsa-stained blood film were performed with the pLDH tests for outpatients with suspected malaria. In total, 460 subjects were recruited: 248 with positive blood films and 212 with negative blood films. Plasmodium falciparum was present in 95% of infections. Sensitivity above 90% was shown by two pLDH tests, Carestart (95.6%) and Vistapan (91.9%), and specificity above 90% by Parabank (94.3%) and Carestart (91.5%). Sensitivity decreased with low parasitaemia (chi(2) trend, P<0.001); however, all tests achieved sensitivity >90% with parasitaemia > or =100/microl. All tests had good inter-reader reliability (kappa>0.95). Two weeks after diagnosis, 4-10% of pLDH tests were still positive compared with 69.7% of the HRP2 tests. All tests had similar ease of use. In conclusion, two pLDH tests performed well in diagnosing P. falciparum malaria, and all pLDH tests became negative after treatment more quickly than the HRP2. Therefore the rapid test of choice for use with artemisinin-combination therapies in this area would be one of these new pLDH tests.

[Evaluation of the Unicel DXC 600 (Beckman Coulter) and comparison with Integra 800 (Roche Diagnostics)]

The Unicel DXC 600 is an automated analytical system from Beckman Coulter for measuring usual biochemistry parameters (electrolytes, substrates and enzymatic activities), therapeutic drugs, drugs of abuse and specific proteins. According to the "Société française de biologie clinique (SFBC)" validation protocol, we tested the following parameters: electrolytes (sodium, potassium, chloride, total CO2), substrates (uric acid, calcium, phosphate, glucose, creatinine, urea, cholesterol, HDL cholesterol, bilirubin, iron, triglycerides), enzymes (ALAT, ASAT, amylase, CK, GGT, LDH, lipase, ALP), total proteins and specific proteins (albumin, CRP, haptoglobin). The results confirm the excellent analytical performances regarding imprecision. The comparison study shows differences between values obtained with Unicel DXC 600 and Integra 800 (Roche diagnostics), leading to the use of correcting factors for some parameters.

Evaluation of polymerase chain reaction and adenosine deaminase assay for the diagnosis of tuberculous effusions in children

AIM

To evaluate and compare the utility of polymerase chain reaction (PCR) for the diagnosis of tuberculous effusions in children.

METHODS

PCR, adenosine deaminase (ADA) activity and absolute lymphocyte count (ALC) were evaluated in the fluid of 31 tuberculous (20 pleural, 8 ascites and 3 pericardial) and 24 non-tuberculous (10 transudtative ascites, 8 empyema thoracis, 3 malignant pleural and 3 pyopericardium) effusions.

RESULTS

Fluid PCR for Mycobacterium tuberculosis was positive in 74% of tuberculous effusions, whereas it was falsely positive in 13% of the non-tuberculous group. The mean fluid ADA and ALC values were significantly higher in tuberculous effusions than in non-tuberculous effusions (p<0.001). The sensitivity and specificity of PCR, ADA (> or =38 IU/l) and ALC (> or =275/mm3) were 74% and 88%, 81% and 75%, and 90% and 83%, respectively, in diagnosing tuberculous effusions. The sensitivity of PCR, ADA and ALC was 100%, 100% and 88%, respectively, for confirmed tuberculous effusions. When the two tests were combined (either/or positive), the sensitivity increased (90-100%) at the expense of specificity. When both the tests were positive, then the specificity markedly increased (92-96%), but sensitivity of the tests decreased.

CONCLUSION

Fluid PCR alone should not be relied on as a single test; rather, combined analysis with either ADA or ALC could be more useful in the diagnosis of tuberculous effusions in children.

IFCC primary reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C

This paper is the eighth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The concept of reference procedures for the measurement of catalytic activity concentrations of enzymes; Part 2. Reference procedure for the measurement of catalytic concentration of creatine kinase; Part 3. Reference procedure for the measurement of catalytic concentration of lactate dehydrogenase; Part 4. Reference procedure for the measurement of catalytic concentration of alanine aminotransferase Part 5. Reference procedure for the measurement of catalytic concentration of aspartate aminotransferase Part 6. Reference procedure for the measurement of catalytic concentration of gamma-glutamyltransferase; Part 7. Certification of four reference materials for the determination of enzymatic activity of gamma-glutamyltransferase, lactate dehydrogenase, alanine aminotransferase and creatine kinase at 37 degrees C. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method. Differences are tabulated and commented on.

Metrological traceability of values for catalytic concentration of enzymes assigned to a calibration material

BACKGROUND

The metrological traceability of values for the catalytic concentration of several enzymes assigned to a calibration material has been assured by following the recently published International Standard ISO 18153.

METHODS

A traceable value with a measurement uncertainty was assigned for the catalytic concentration of alanine aminotransferase, creatine kinase, gamma-glutamyltransferase and lactate dehydrogenase in two materials from different sources. These are all measurable quantities, with the primary reference measurement procedure described by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) and a primary calibrator giving metrological traceability to the SI unit of measurement. The metrologically traceable calibration was validated by measuring human serum samples using the primary reference measurement procedure and a routine commercial measurement procedure calibrated with the traceable materials.

RESULTS

Results showed that the primary reference procedure, selected manufacturers' procedures and the end-user's routine procedure for each enzyme have the same analytical specificity. Four of eight commercial calibrators tested were commutable, whereas the others had a very small difference in absolute terms, indicating that these materials would be useful for calibration.

CONCLUSION

The implementation of a reference system for enzyme measurements was demonstrated that assures the traceability of patient results to SI units.

Trueness verification and traceability assessment of results from commercial systems for measurement of six enzyme activities in serum

BACKGROUND

The in vitro diagnostics directive of the European Union requires traceability to higher order reference measurement procedures and materials for analytes in assuring the result trueness and comparability of laboratory measurements. Manufacturers must ensure that the systems they market are calibrated against available reference systems. Validation of metrologically traceable calibrations is, however, required.

METHODS

A commutable serum-based material was analyzed in three reference laboratories and target values for six enzymes (ALT, AST, CK, GGT, LD, amylase) were assigned using IFCC reference measurement procedures. 70 laboratories in Germany, Italy, and The Netherlands measured the same enzymes in the material using procedures from six commercial companies. A system for maximum allowable error was developed from the biological variation model and the results of the various procedures were tested on their compliance to trueness and between-laboratory and within-laboratory variations relative to the maximum allowable.

RESULTS

For ALT results were relatively good. >95% of laboratories using systems from Dade, Olympus, Ortho and Roche are expected to comply traceability within the biologically derived limits, and 94% respectively 89% from Abbott and Beckman. For AST and GGT only Dade respectively Olympus fully complied. For CK all companies showed significant bias. Nevertheless >95% of laboratories applying Abbott, Beckman and Roche systems will comply. Finally, LD and amylase measurements require significant improvement. Some manufacturers continue to sell on the European market assays giving results which are not traceable to the internationally accepted reference systems.

CONCLUSIONS

The traceability of enzyme measurements obtained with routine procedures to internationally accepted IFCC reference systems is not yet satisfactorily accomplished in clinical practice.

Intermethod calibration of alanine aminotransferase (ALT) and γ-glutamyltransferase (GGT) results: application to Fibrotest® and Actitest® scores

Two multi-component scores (Fibrotest

The choice of conditions for cathepsin D activity determination in human saliva

The aim of the study was the demonstration and choice of conditions for the determination of cathepsin D activity in human mixed saliva. The 6% solution of hemoglobin, denatured with hydrochloric acid, was used as the substrate. The ratio of saliva volume to hemoglobin was 4:1 w/v. The reaction was interrupted by adding 10% trichloroacetic acid, after 6 hours of incubation at 37 degrees C. The increase in degradation products was determined with the use of Folina and Ciocalteau method with copper modification.

A rapid enzyme-linked assay for ADAMTS-13

BACKGROUND

A deficiency in the plasma metalloprotease ADAMTS-13 is associated with deposition of microvascular thrombi that cause thrombotic thrombocytopenic purpura. Current assays for ADAMTS-13 are technically complex and time-consuming. The objective of this study is to devise a rapid and sensitive assay for ADAMTS-13 activity in plasma and verify the site of cleavage.

METHOD

A new enzyme-linked substrate, which contains a core ADAMTS-13-specific peptide conjugated to horseradish peroxidase (HRP) at the N-terminus, and labeled with biotin at the C-terminus, was constructed. After cleavage of this substrate by plasma ADAMTS-13 and removal of uncleaved substrate by adsorption with streptavidin-agarose, ADAMTS-13 activity was quantitated by determining the unadsorbed HRP activity remaining in solution. Levels of inhibitory antibodies in test plasma were also determined by measuring the residual ADAMTS-13 activity after varying amounts of test plasma were incubated with a known amount of ADAMTS-13.

RESULTS

Plasma ADAMTS-13 activity was readily determined in approximately 60 min (coefficient of variation 5.8%) using 1 microL of test plasma. Amino acid sequencing of the cleavage product confirmed that cleavage occurred at the Tyr1605-Met1606 bond in the substrate. ADAMTS-13 activities in the plasma of five TTP patients were below 2%. Inhibitory antibody titers in these samples varied from undetectable to 81 BU mL(-1).

CONCLUSION

The HRP-linked substrate provides a rapid, sensitive, and reproducible way of determining the levels of ADAMTS-13 activity and inhibitory antibodies in plasma.

A new enzymatic cycling method for ammonia assay using NAD synthetase

BACKGROUND

Ammonia is an important marker for liver diseases such as hepatitis and hepatic cirrhosis. Several methods have been developed for ammonia analysis. In particular, the enzymatic assay using glutamate dehydrogenase has been widely used. However, this method is not necessarily high in sensitivity and accuracy due to inhibition by interferences in plasma and instability over long-term storage.

METHODS

We developed an ammonia assay using a system consisting of three enzymes, NAD synthetase (NADS; EC 6.3.1.5), glucose dehydrogenase (GlcDH; EC 1.1.1.47), and diaphorase (DI; EC 1.6.99.2).

RESULTS

The calibration curve for ammonia with the cycling method was linear (r=0.999) up to 300 micromol/l. The within-run CVs of 10 and 20 micromol/l NH4Cl solutions and 24.1 micromol/l ammonia in human plasma were 2.3%, 1.5%, and 2.8%, respectively. The between-run CVs of them were 4.5%, 3.1%, and 2.8%, respectively. The recovery was between 96.3% and 105%, and the limit of detection was 2.4 micromol/l. No significant interference was observed with addition of the following components: hemoglobin, bilirubin, chyle, EDTA, heparin, and sodium citrate. Due to the high degree of specificity of NAD synthetase to ammonia, no amino compounds exhibited any effect on the ammonia assay. A high correlation was obtained between results of the present method (y) and a conventional glutamate dehydrogenase method in regression analysis; y=0.944x-6.160 with r=0.993 (n=125). However, an addition error was observed from Bland-Altman analysis (the 95% limits of agreement between the two methods; 9.51+/-5.92 micromol/l).

CONCLUSION

This new enzymatic method is more sensitive, precise, and accurate than the conventional method. In particular, accurate assay for ammonia can be performed without interference in the presence of various compounds.

[Predictors of choledocholithiasis in patients sustaining acute biliary pancreatitis]

BACKGROUND

To assess the role of alkaline phosphatase (AP), gamil-glutamyltransferase (gammaGT) and abdominal ultrasound (US) as predictors of choledocholithiasis in patients sustaining acute biliary pancreatitis.

METHODS

Data was prospectively collected during a period of 31 months. Forty patients were included, 30 were female and the mean age was 49 +/- 16. All patients sustaining acute biliary pancreatitis were enrolled. Patients with clinical jaundice and severe pancreatitis were excluded. Serum content of AP and gGT as well as US were assessed at admission and 48 hours before cholecistectomy. All patients underwent intra-operative cholangiography (IOC) or pre-operative endoscopic retrograde cholangiography (ERCP), which was indicated based on the odds of choledocholithiasis. In order to identify the predictors of choledocholithiasis, variables were compared between patients sustaining or not such alteration in cholangiography. Student t, Fisher and chi square tests were used for statistical analysis, considering p<0.05 as significant. Positive (PPV) and negative predictor values (NPV) were calculated for each variable.

RESULTS

Upon admission, 15 (37%) patients sustained biliary tract dilatation and 5 (12%) choledocholithiasis at the US. Forty eight hours before the operation, 34 (85%) patients had altered levels of gGT and 16 (40%) of AP. Pre-operative US showed biliary tract dilatation in nine patients and choledocholithiasis in three. ERCP was performed in 15 (37%) cases. Higher PPV (55%) was attributed to pre-operative US, which had also a NPV of 96%.

CONCLUSION

The best predictor of choledocholithiasis in patients sustaining mild acute pancreatitis was the biliary tract dilatation in pre-operative US.

Reference intervals for eight enzymes in blood of adult females and males measured in accordance with the International Federation of Clinical Chemistry reference system at 37 degrees C: part of the Nordic Reference Interval Project

As part of the Nordic Reference Interval Project we present reference intervals for alanine transaminase (ALT), aspartate transaminase (AST), creatine kinase (CK), lactate dehydrogenase (LD), alkaline phosphatase (ALP), gamma-glutamyltransferase (GT), amylase (AMY) and pancreatic type of AMY in blood of adult males and females. A total of 3036 reference persons, all of whom considered themselves to be in good health, were recruited by 102 Nordic clinical biochemical laboratories. Exclusions were undertaken on the basis of predefined biochemical and clinical criteria. Enzyme activities in serum and plasma were measured in the different laboratories using various commercially available routine measurement systems at 37 degrees C. Only results obtained with the International Federation of Clinical Chemistry (IFCC) compatible measuring systems were selected for estimation of the enzyme reference intervals. The final number of results on each enzyme varied from 459 (LD) to 2300 (ALT). The 2.5 and 97.5 percentile reference limits were calculated by a non-parametric method in accordance with the IFCC recommendations, using the Refval 4.0 data program. Statistical partitioning testing was undertaken to decide whether the reference intervals ought to be partitioned according to gender and/or age. For most of the enzymes, but not for all, the upper reference limits were found to be higher than those that have been in general use until now.

[Uncertainty of measurement as an integral part of the result and a tool of quality of work improvement for the chemical-toxicology laboratory]

An uncertainty in measurements is a numerical defined range that is supposed to find a true value with a given level of probability. The purpose of this study was to estimate a type A and B of uncertainty in the analysis of ethanol using the ADH method and prove it to be useful in lab practice. A large percentage of uncertainty was shown for pipetting of the ADH and perchloric acid solutions. This result formed the basis to make an effort in order to improve the procedure. The results of uncertainty of measurements given by method B are similar to the empiric method A results. The reduction of expenses and time saving of the analysis is an important advantage of the described way of uncertainty.

Faecal pancreatic elastase--1 a non invasive measure of exocrine pancreatic function

BACKGROUND

Faecal pancreatic elastase-1 is a laboratory based test used for the diagnosis or exclusion of exocrine pancreatic insufficiencies. Pancreatic elastase-1, is released into blood circulation during inflammation of the pancreas, but unlike most pancreatic enzymes it is stable during intestinal passage and not degraded.

OBJECTIVES

The major objective of this work was to establish the assay of faecal pancreatic elastase-1 in spot stool samples as an exocrine pancreatic function test at Korle-Bu (a referral) hospital in Ghana, for the diagnosis of pancreatic diseases.

METHOD

Twenty-five apparently healthy persons; mean age of 43.4 years and thirty-two patients with various pancreatic diseases, mean age 51.4 years were referred for the test based on clinical presentation, imaging studies and biopsy findings. The male to female ratio was 6.4:3.6 and 8.1:1.9 respectively. An ELISA technique which recognizes human pancreatic elastase-1 from spot stool samples was employed for the test and read photometrically at 405nm.

RESULTS

Elastase-1 activity in spot stool samples from apparently healthy group ranged from 165 to 870mg/g with a mean of 379 (SE 41)mg/g, and a range of 20 to 285mg/g with a mean of 112.9 (SE 11.6)mg/g obtained for the pancreatic disease group. Disease severity was classified as mild to moderate with elastase-1 concentration between 100 and 200mg/g stool and the severe pancreatic insufficiency group with elastase-1 concentration of less than 100mg/g stool. The pancreatic elastase-1 was found to be stable in faeces for several weeks when stored frozen, hence the convenience for batch determinations.

CONCLUSION

The test is non invasive and can assist with the diagnosis of inflammatory conditions of the pancreas where imaging results are equivocal.

Inaccuracy of routine creatinine measurement in canine urine

BACKGROUND

Urine creatinine concentration often is used in ratios such as urine protein:creatinine to compensate for dilution or concentration of spot urine samples.

OBJECTIVE

The purpose of this study was to compare the accuracy of different techniques of urine creatinine measurement currently available for veterinary practitioners.

METHODS

In 104 samples of canine urine diluted 1:20 with distilled water, creatinine concentration was measured using a kinetic Jaffé reaction assay, and an enzymatic technique on an automatic analyzer (Elimat) and 3 benchtop analyzers (Reflovet, Scil; Vitros DT2, Ortho-Clinical Diagnostics; Vettest 8008, IDEXX) used in veterinary practice.

RESULTS

The Jaffé and enzymatic techniques on the Elimat were not significantly different, and their inaccuracy tested with human control urines was <5%. The benchtop analyzers underestimated creatinine concentration, especially at concentrations >2000 mg/L. Inaccuracy was higher with multilayer slide technology systems (Vitros and Vettest) than with the Reflovet system. Results were approximately 25% and 2% lower, respectively, than with the Elimat at urine creatinine concentrations about 2000 mg/L.

CONCLUSION

Inaccuracy in urine creatinine measurements using benchtop analyzers should be taken into account when defining decision thresholds, which should be corrected according to the method used to avoid misinterpretations.

Comparison between the enzymatic vitros assay for creatinine determination and three other methods adapted on the Olympus analyzer

To evaluate the relationship between the enzymatic Vitros assay for creatinine determination and other methods, we determined creatinine concentration in 400 heparin samples. Plasma creatinine level was successively determined on the Vitros 750 analyzer (Johnson & Johnson Co., Rochester, NY) and on the Olympus AU2700 analyzer (Olympus France, Rungis, France), using three reagents in the same assay: Olympus-Jaffé and two enzymatic commercial kits-Crea Plus (Roche Diagnostics, Meylan, France) and Enzymatic Creatinine (Randox, Mauguio, France). Comparison of Jaffé and enzymatic measurements of plasma creatinine levels revealed a high correlation when considering all values ranged from 20-1000 micromol/l (r > 0.99). However, for values <60 micromol/l, enzymatic reagents provided best results. Enzymatic methodology is a better clinical choice for the accurate measurement of creatinine, especially for neonates, pediatrics, and hematology units. Because analytical performance and the costs of Randox creatinine were satisfactory for our laboratory, this method, adapted on the Olympus analyzer, was chosen for routine determination of creatinine levels. According to the Valtec protocol (8), no interferences such as hemolysis, lipemia, or bilirubin were detected for Enzymatic Creatinine Randox.

Multicenter evaluation of the commutability of a potential reference material for harmonization of enzyme activities

Standardization of laboratory results allows for the use of common reference intervals and can be achieved via calibration of field methods with secondary reference materials. These harmonization materials should be commutable, i.e., they produce identical numerical results independent of assay principle or platform. This study assessed the commutability of a cryolyoprotectant-containing harmonization material, obtained from the Dutch Foundation for Quality Assessment in Clinical Laboratories, that is intended to harmonize measurements of enzyme activities within the Dutch project “Calibration 2000”. The catalytic concentrations of alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, γ-glutamyltransferase and creatine kinase were analyzed in pooled patient sera and in the reference material in 14 laboratories. On liquid chemistry analyzers the harmonization material behaves like patient material. The enzyme activities measured in it fall on the regression lines calculated from activities measured in serum samples. For dry chemistry analyzers the activities of all enzymes measured in the harmonizator differ from the serum-based regression line. We show that this is due to the sucrose-containing cryolyoprotectant in the harmonization material. For each enzyme, correction factors were calculated that compensated for the bias and proved to be constant between reagent lots. Depending on the enzyme activity measured, application of these factors leads to 2- to 10-fold reduction of between-laboratory percentage coefficient of variation. Thus, additives to (potential) reference materials may alter their matrix in a way that interferes with analysis on certain test systems. The bias caused may be quantifiable and correctable. Establishment of correction factors leads to analytical uncertainties and costs. Therefore, matrix-based materials without additives should be selected as reference materials.

Establishment of reference intervals for enzyme catalytic activity concentration measurements at 37 degrees C--a practical approach

The change from measuring enzyme catalytic activity concentrations from 25 degrees C to 37 degrees C in the German Federal Republic has led to the need for new reference ranges for defined patient groups and for healthy individuals. Up to now, these are only present as tentative values and are incomplete, especially for children. This article describes a method for deriving reference ranges from results obtained from measurement at 25 degrees C and 37 degrees C and the use of percentiles to establish values for 37 degrees C. A total of 1,111,378 data from 507,305 patients were used to establish reference ranges for the following 11 enzymes at 37 degrees C using the test kits from Roche Diagnostics measured on the Modular analyser: acid phosphatase, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, cholinesterase, creatine kinase, creatine kinase - MB subunit, gamma glutamyl transpeptidase, glutamate dehydrogenase, lactate dehydrogenase and lactate dehydrogenase - isoenzyme 1. The computed reference ranges from the data used gave rise to reference ranges, some of which were in agreement with the data from the producer, some of which, however, showed deviations from the values given by the producer. Ranges for newborns, children and adolescents could be computed with the prerequisite that ranges for 25 degrees C were available and that these had been established and validated. This method of establishing reference ranges for catalytic enzyme activities can be used for all producers, providing the number of data used is sufficient to allow for valid statistical analysis.

Measurement of von Willebrand factor-cleaving protease (ADAMTS-13) activity in plasma: a multicenter comparison of different assay methods

A severely deficient ADAMTS-13 activity (<5%) is a key laboratory finding confirming the diagnosis of thrombotic thrombocytopenic purpura (TTP), whereas a mildly or moderately decreased activity is found in various other conditions. Laboratory tests for ADAMTS-13 activity must reliably identify a severe deficiency and detect inhibitory antibodies against ADAMTS-13. We carried out a multicenter comparison of different assays for ADAMTS-13 activity in plasma, including the quantitative immunoblotting of degraded von Willebrand factor (VWF) substrate, the residual collagen binding activity and ristocetin cofactor activity of degraded VWF, and an immunoradiometric assay. The main goal was to investigate whether all assays concordantly identified severe ADAMTS-13 deficiency and detected inhibitory antibodies. ADAMTS-13 activity was determined by five laboratories in 30 plasma samples of patients with hereditary and acquired TTP and other conditions. ADAMTS-13 activity values of the samples ranged from <3% to > 100%. Concerning the identification of a severe ADAMTS-13 deficiency, good interassay and interlaboratory agreement was observed with only one false-negative and two false-positive results by two laboratories using a collagen binding assay. For samples with normal or mildly to moderately reduced ADAMTS-13 activity, results were less concordant. There was good agreement for the detection of strong inhibitors. We conclude that all assays investigated are useful as a screening test in suspected TTP. Further assay improvement is needed, however.

IFCC primary reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C. International Federation of Clinical Chemistry and Laboratory Medicine. Part 4. Reference procedure for the measurement of catalytic concentration of alanine aminotransferase

This paper is the fourth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of Gamma-Glutamyltransferase; Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of Gamma-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C. A document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method. Differences are tabulated and commented on in Appendix 2.

IFCC primary reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C. International Federation of Clinical Chemistry and Laboratory Medicine. Part 5. Reference procedure for the measurement of catalytic concentration of aspartate aminotransferase

This paper is the fifth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of Gamma-Glutamyltransferase; Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of Gamma-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C. A document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method. Differences are tabulated and commented on in Appendix 3.

A rapid direct telomerase assay method using 96-well streptavidin plates

We have developed a high-throughput direct assay methodfor the assay of telomerase activity that improves on previous direct telomerase assays in two ways that allow larger numbers of samples to be conveniently processed: (i) 96-well streptavidin coated plates are used to bind and wash biotinylated primer extension products from the telomerase assay, as opposed to tubes containing streptavidin-coated magnetic beads; and (ii) storage phosphor-imagery is used instead of film autoradiography to detect telomerase products after being washed and released from the streptavidin-derivatized matrix. This method improves on previous direct assay methods using magnetic beads by allowing larger numbers of samples to be conveniently assayed. Also, the total activity of the radiolabeled nucleotides used in this procedure is significantly lower than that used in standard direct telomerase assays, lowering costs and exposure to radioactivity. We have validated the assay by repeating, in triplicate, the IC50 determination of rivanol, our previously identified telomerase inhibitor.

Molecular study of the hydroxymethylbilane synthase gene (HMBS) among Polish patients with acute intermittent porphyria

Acute intermittent porphyria (AIP), an autosomal dominant disorder of heme biosynthesis, is due to mutations in hydroxymethylbilane synthase (HMBS; or porphobilinogen deaminase, PBGD) gene. In this study, we analyzed 20 Polish patients affected by AIP and we were able to characterize seven novel mutations. A nonsense mutation (Y46X), two frameshift mutations (315delT and 552delT) and a 131bp deletion (nucleotides 992-1123) give rise to truncated proteins. A donor splice site mutation IVS12+2T>C predicts skipping of exon 12. A missense mutation (D61Y) was identified in two apparently unrelated patients with a clearly clinical indication of AIP. An inframe 3-bp deletion (278-280delTTG) results in the removal of V93 from the enzyme. In addition to the novel mutations, nine previously described HMBS gene mutations-R26H, G111R, IVS7+1G>A, R149X, R173Q, 730-731delCT, R225X, 982-983delCA and G335D-were identified in this cohort. Our results demonstrate that molecular analysis of the PBGD gene is a more reliable method comparing to enzymatic assay in the diagnosis of AIP. Although more than 170 different mutations are known to the HMBS gene so far, over 40% of all mutations identified among the Polish AIP patients of this study are novel mutations, indicating the heterogeneity of molecular defects causing AIP.

IFCC Primary Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes at 37°C. Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of γ-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase according to IFCC Reference Procedures at 37°C

This paper is the seventh in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of Gamma-Glutamyltransferase. A document describing the determination of preliminary reference values is also in preparation. The certification of the catalytic activity concentrations as determined by the recently elaborated IFCC primary reference methods at 37 degrees C of four enzyme preparations, namely IRMM/IFCC 452 (gamma-glutamyltransferase), IRMM/IFCC 453 (lactate dehydrogenase 1), IRMM/IFCC 454 (alanine aminotransferase) and IRMM/IFCC 455 (creatine kinase) is described. Homogeneity data were derived from previous results. Stability was assessed using recently obtained data as well as data from previous stability studies. The collaborative study for value assignment was performed under a strict quality control scheme to ensure traceability to the primary reference method. Uncertainty of the materials was assessed in compliance with the Guide to the Expression of Uncertainty in Measurement. The certified values obtained at 37 degrees C are 1.90 microkat/l +/- 0.04 microkat/l (114.1 U/l +/- 2.4 U/l), for gamma-glutamyltransferase, 8.37 microkat/l +/- 0.12 microkat/l (502 U/l +/- 7 U/l), for lactate dehydrogenase 1, 3.09 microkat/l +/- 0.07 microkat/l (186 U/l +/- 4 U/l), for alanine aminotransferase and 1.68 microkat/l +/- 0.07 microkat/l (101 U/l +/- 4 U/l), for creatine kinase. The materials are intended for internal quality control as well as for the evaluation of test systems as required by recent European Union legislation. Furthermore, the materials can be used to transfer accuracy from a reference method to a routine procedure provided the procedures exhibit the same analytical specificity and the certified materials are commutable.

IFCC Primary Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes at 37C. Part 6. Reference Procedure for the Measurement of Catalytic Concentration of γ-Glutamyltransferase

This paper is the sixth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of Gamma-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C A document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method. Differences are tabulated and commented on in Appendix 1.

[Improvement of inter-laboratory imprecision in enzyme measurements]

The traceability chains of the enzyme measurement system were established based on technological advances in instrumentation and reagent systems. The values assigned in reference materials (Japan Certified Enzyme Reference Materials; JCERM) were transferred to daily laboratory analysis via enzyme calibrators included in industrial reagent kits. The imprecision between laboratories was then minimized to within 4 percent in six enzymes, AST, ALT, LD, ALP, CK and gamma-GT.

Establishing a reference system in clinical enzymology

The goal of standardization for measurements of catalytic concentrations of enzymes is to achieve comparable results in human samples, independent of the reagent kits, instruments and laboratory where the procedure is carried out. To pursue this objective, the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) has launched a project to establish a reference system in clinical enzymology. This system is based on three hinges: a) extensively evaluated and carefully described reference procedures, b) certified reference materials and c) a network of reference laboratories operating in a highly controlled manner. The original IFCC-recommended procedures for alanine aminotransferase, aspartate aminotransferase, creatine kinase, gamma-glutamyltransferase, lactate dehydrogenase and alpha-amylase have been slightly modified to optimize them at 37 degrees C, with the definition of detailed operating procedures. A group of laboratories perform these procedures manually, with self-made reagents on carefully calibrated instruments. Partially purified and stabilized materials, prepared in the past by the Community Bureau of Reference, have been re-certified by these laboratories for alanine aminotransferase, creatine kinase, gamma-glutamyltransferase and lactate dehydrogenase activities. Using these materials and the manufacturer's standing procedures, industry can assign traceable values to commercial calibrators. Thus, clinical laboratories, which will use routine procedures with these validated calibrators to measure human specimens, can finally obtain values which are traceable to reference procedures.

Drug interference in clinical chemistry: recommendation of drugs and their concentrations to be used in drug interference studies

A group of international experts prepared two lists of drugs with their serum/plasma and urine concentrations, which should be used when evaluating the performance of a new laboratory method. The two lists were verified by running in vitro interference studies in three European laboratories on Hitachi instruments. The study identified the following new interferants: acid phosphatase in serum by ibuprofen and theophylline; non-prostatic acid phosphatase in serum by cefoxitin and doxycycline; creatine kinase MB in serum by doxycycline; total bilirubin in serum (Jendrassik-Grof method) by rifampicin and intralipid; total bilirubin in serum (DPD method) by intralipid; creatinine in serum (Jaffe method) by cefoxitin; fructosamine in serum by levodopa and methyldopa; uric acid in serum by levodopa, methyldopa and tetracycline; carbamazepine in serum by doxycycline, levodopa, methyldopa and metronidazole; digitoxin in serum by rifampicin; phenytoin in serum by doxycycline, ibuprofen, metronidazole and theophylline; theophylline in serum by acetaminophen, cefoxitin, doxycycline, levodopa, phenylbutazone and rifampicin; tobramycin in serum by cefoxitin, doxycycline, levodopa, rifampicin and phenylbutazone; valproic acid in serum by phenylbutazone; C3 in serum by intralipid; C4 in serum by doxycycline; rheumatoid factor in serum by ibuprofen and metronidazole; pancreatic amylase and total amylase in urine by acetylcysteine, ascorbic acid, cefoxitin, gentamicin, levodopa, methyldopa and ofloxacin; magnesium in urine by acetylcysteine, gentamicin and methyldopa; beta2-microglobulin in urine by ascorbic acid; total protein in urine by ascorbic acid, Ca-dobesilate and phenylbutazone. Interference in acid phosphatase, creatine kinase MB and bilirubin methods was observed at very low analyte concentrations, and therefore it may not be evident at higher concentrations. The study confirmed the usefulness of the recommendation.