Establishment of reference intervals of clinical chemistry analytes for the adult population in Egypt

BACKGROUND

This is the first Egyptian nationwide study for derivation of reference intervals (RIs) for 34 major chemistry analytes. It was conducted as a part of the global initiative by the IFCC Committee on Reference Intervals and Decision Limits (C-RIDL) for establishing country-specific RIs based on a harmonized protocol.

METHODS

691 apparently healthy volunteers aged ≥18 years were recruited from multiple regions in Egypt. Serum specimens were analyzed in two centers. The harmonization and standardization of test results were achieved by measuring value-assigned serum panel provided by C-RIDL. The RIs were calculated by parametric method. Sources of variation of reference values (RVs) were evaluated by multiple regression analysis. The need for partitioning by sex, age, and region was judged primarily by standard deviation ratio (SDR).

RESULTS

Gender-specific RIs were required for six analytes including total bilirubin (TBil), aspartate and alanine aminotransferase (AST, ALT). Seven analytes required age-partitioning including glucose and low-density lipoprotein cholesterol (LDL-C). Regional differences were observed between northern and southern Egypt for direct bilirubin, glucose, and high-density-lipoprotein cholesterol (HDL-C) with all their RVs lower in southern Egypt. Compared with other collaborating countries, the features of Egyptian RVs were lower HDL-C and TBil and higher TG and C-reactive protein. In addition, BMI showed weak association with most of nutritional markers. These features were shared with two other Middle Eastern countries: Saudi Arabia and Turkey.

CONCLUSION

The standardized RIs established by this study can be used as common Egyptian RI, except for a few analytes that showed regional differences. Despite high prevalence of obesity among Egyptians, their RVs of nutritional markers are less sensitive to increased BMI, compared to other collaborating countries.

Internal quality assurance of HIL indices on Roche Cobas c702

Automatic assessment of hemoglobin (H), lipaemia (L) and icterus (I) in serum or plasma (HIL indices) is the mainstay for evaluating sample quality. We planned this study to verify whether in-house prepared internal quality control (IQC) materials may be suitable for quality assurance of HIL indices. Pools containing different values of each of the three HIL indices were prepared from routine plasma samples, divided in aliquots and frozen at -20°C. Stability of frozen materials was assessed by thawing one aliquot of each pool after different days of freezing (1, 4, 8, 15, 22 and 29), and by measuring HIL indices on baseline fresh samples and frozen-thawed aliquots with Roche Cobas c702. Five fresh liquid IQCs materials were also measured at the same time points. Intra-assay and inter-assay imprecision of HIL indices calculated with commercial IQC materials ranged between 1.1-2.0% and 1.6-3.3%, respectively. When target values of HIL indices were calculated using frozen-thawed aliquots, the inter-assay imprecision of in-house prepared materials was optimal, even better than that of commercial liquid IQCs (H-index, 0.8% versus 1.6%; L-index, 2.2% versus 2.5%; I-index, 0.8% versus 3.3%). In conclusion, in-house prepared IQC materials are cost-effective alternatives to commercial liquid IQCs for HIL quality assurance.

Increased conjugated bilirubin is sufficient to initiate screening for biliary atresia

INTRODUCTION

Biliary atresia is the leading cause of liver transplantation in children. It affects 1:15,000 in Denmark. With a national birth rate of 60,000, four children are born every year with biliary atresia. Early correction of biliary obstruction is essential to prevent fatal biliary cirrhosis. The Danish Health and Medicines Authority (DHMA) demands diagnostic evaluation of children with elevated level of serum bilirubin after two weeks of age. Biliary atresia has to be excluded if conjugated bilirubin level is above than 20 μmol/l, and/or more than 20% of total bilirubin. This percentage value has caused diagnostic trouble over the years. The objective of the present study was to investigate the possibility of changing the recommendations.

METHODS

This was a retrospective analysis of the medical records of children operated for biliary atresia in the 1993-2012 period.

RESULTS

During the period, 73 patients where operated with a portoenterostomy ad modum Kasai. Patients older than 84 days at the time of operation were excluded, 54 patients were available for analysis. Conjugated bilirubin in μmol/l and the percentage value were significantly above the DHMA threshold limit: mean 129.7 μmol/l (42-334 μmol/l) and 73% (28-97%), respectively.

CONCLUSION

The total amount of conjugated bilirubin above 20 μmol/l is sufficient to require further evaluation for biliary atresia. The percentage value is unnecessary and may cause confusion.

FUNDING

none.

TRIAL REGISTRATION

not relevant.

Correlation and precision of serum free bilirubin concentrations determined by single and two peroxidase concentration methods in term or late-preterm newborn infants using a FDA-approved analyzer

BACKGROUND

Free bilirubin concentration (B(f)) is an index for identifying newborns at risk for developing bilirubin-induced neurotoxicity. It has been suggested that B(f) measured by a single peroxidase concentration (B(f-single)) does not equal the equilibrium concentration of B(f), which is confirmed by B(f) at two different peroxidase concentrations (B(f-two)). However, the differences between B(f-single) and B(f-two) are unknown in the serum of term or late-preterm newborn infants. Furthermore, to apply B(f-single) with savings on time and cost to the clinical setting, it is very important for us to clarify the differences between B(f-single) and B(f-two).

METHODS

Forty serum samples were obtained from 21 term or late-preterm newborns who were admitted at Kobe University Hospital. Using a peroxidase method, B(f-single) was measured at one peroxidase concentration, and B(f-two) was determined at two different peroxidase concentrations (the manufacturer's recommended peroxidase concentration and half the manufacturer's recommended peroxidase concentration). To clarify the relationship between B(f-single) and peroxidase concentrations, B(f-single) was measured at five different concentrations of peroxidase reagent. Intra-day and inter-day analyses were performed to assess the precision of B(f-single) and B(f-two).

RESULTS

1/B(f-single) increased as peroxidase concentration increased. B(f-single) was significantly lower than B(f-two) (B(f-single): 0.50 microg/dL [0.13 - 1.22 microg/dL] versus B(f-two): 0.59 microg/dL [0.15 - 1.76 microg/dL], p < 0.001), but B(f-single) was significantly correlated with B(f-two) (r = 0.953, p < 0.0001). Intra-day analysis showed that the CV was 9.7% for B(f-two) and 3.3% for B(f-single), and the inter-day CV was 12.4% for B(f-two) and 3.2% for B(f-single).

CONCLUSIONS

Although B(f-single) and B(f-two) are not identical, B(f-single) is significantly correlated with B(f-two) and it is more precise than B(f-two) in term or late-preterm newborns.

Do we measure bilirubin correctly anno 2005?

We observed 30% discrepancy between liquid chemistry and dry chemistry analysers for the determination of total bilirubin in human adult serum samples, which were consistent with a 20% overestimation and 10% underestimation relative to a Jendrassik-Grof reference method, respectively. In contrast, standard reference material SRM916, which was recently recommended as being the most suitable material for attaining interlaboratory agreement, shows very good agreement on both types of analysers, as well as close to 100% recovery with respect to the reference method. We show that the liquid vs. dry bilirubin discrepancies seem to originate in the presence of either conjugated or δ-bilirubin. Our observations make it clear that good interlaboratory (or inter-analyser) agreement between bilirubin reference materials does not guarantee the same for bilirubin concentrations in human serum samples.

[Using purified conjugated bilirubin as a calibrator for bilirubin measurement]

OBJECTIVES

To improve the accuracy and precision of the determination of bilirubin, especially direct bilirubin (DB), and the standardization of that as well.

METHODS

Purified conjugated bilirubin (Bc) and ditaurobilirubin(DTB) and their diazo products were subjected to absorption spectrum analysis. The diazo reaction characters of their calibration solutions were compared by the method of Doumas J-G(TB & DB).

RESULTS

Bc, DTB and their azopigments were found to have the similar absorption spectra with the same lambda max. Their TB standard curves almost superposed together all over. Although the slopes of their DB standard curves were not markedly different ((YBc = 0.00366X + 0.00933, rBc2 = 0.9977, P < 0.01; YDTB = 0.00391X + 0.00023, rDTB2 = 0.9987, P < 0.01; Pb1-b2 > 0.05, n1 = n2 = 5), the DB value measured for Bc differed from that for DTB(n = 5, P < 0.05). In addition, the calibrators made from Bc based different matrices, such as HSA, BSA and human serum, were significantly different in DB/Bc, but no difference was seen among the concentrations. Furthermore, the DB values determined for DTB or Bc increased linearly with the corresponding concentrations, respectively, with no difference between the slopes (YBc = 0.8300XBc + 1.9463, rBc2 = 0.9977, P < 0.01; YDTB = 0.8853XDTB-0.0251, rDTB2 = 0.9986, P < 0.01; n1 = n2 = 5, Pb1-b2 > 0.05).

CONCLUSIONS

The results demonstrate that the diazo reaction characters of Bc are identified with those of DTB. However, under the condition of DB, Bc reacts differently from DTB. This study also indicates that as a calibrator of DB based human serum, Bc has the similar constant effect of HCl as serum samples do, so it is a more reliable calibrator to eliminate the matrix effects.

A modification of the acid diazo coupling method (Malloy-Evelyn) for the determination of serum total bilirubin

A simple and reliable method for the determination of total bilirubin from human serum is described. In this method, indirect bilirubin is liberated by the tenside in 0.12 mol l-1 HCl (R1), and the total bilirubin is coupled with a 2,5-dichlorobenzene diazonium (DBD) salt to obtain the corresponding azobilirubin having a lambda max of about 520-522 nm. The method can easily be applied to the KONE Delta, a fully automated, discrete random access clinical analyser, and also to less modern instruments. A sample volume of 5 microliters, R1 volume of 180 microliters, and R2 volume of 36 microliters was used on the KONE Delta. After a 5-min incubation at 37 degrees C, measurement at 575 nm was done (main wavelength). The within-run imprecision (CV%) varied from 2.9 to 0.3% within the serum total bilirubin range of 14-290 mumol l (n = 10). The between-run imprecision was from 2.2 to 1.3% within the range 13-97 mumol l-1 (n = 8). The method is linear up to at least 340 mumol l-1 (19.8 mg dl-1), and dilution extends the test limit to 3400 mumol l-1 (198.8 mg dl-1). The linearity of dilution was good over the practical measuring range. The present method had a strong linear correlation with the Boehringer 2,5-dichlorophenyl diazonium (DPD) method on the Hitachi 717 analyser: y(DBD) = 1.018x(DPD)+0.758, r = 0.9955 (n = 61). The stability of R2 (diazo reagent) in the analyser reagent compartment lasts at least 2 weeks.

Transcutaneous bilirubinometry: its role in the assessment of neonatal jaundice

OBJECTIVE

To review the literature on transcutaneous bilirubinometry so that its exact role in the prevention of kernicterus or bilirubin encephalopathy could be determined.

DESIGN AND METHODS

Literature searches were done in Medline and Current Contents.

RESULTS

It is estimated that about 50% of newborns have an episode of jaundice in the first few days of life. Six percent of newborns may develop hyperbilirubinemia (> 220 mumol/L), which can potentially cause bilirubin encephalopathy or kernicterus, a severe neonatal disease. In the past, serum bilirubin (SB) has been the preferred method of detecting hyperbilirubinemia in newborns. The ordering of SB in neonates is based on visual evaluation by either physicians or nursing staff. Skin puncture collection of blood exposes the neonate to trauma and risk of infection. A noninvasive device for predicting serum bilirubin levels in newborns diminishes the need to do skin punctures. One such device that has been very extensively studied is the Minolta AirShields Jaundice Meter. It is a portable light-weight instrument that uses reflectance measurements on the skin to determine the amount of yellow color present in the skin, namely transcutaneous bilirubin (TcB). Although the TcB measurements correlate well with serum bilirubin (SB) levels, they cannot accurately predict serum bilirubin because of error related to a variety of factors.

CONCLUSIONS

TcB cannot be used directly to make decisions about transfusions or phototherapy in neonates. It is a good tool for screening neonates to determine when a laboratory measurement of serum bilirubin is needed. Such a practice requires careful selection of the decision level so that false-negative TcB values do not prevent appropriate serum bilirubin tests from being done.

A survey of the values of clinical chemistry parameters obtained for a common rat blood sample in ninety-eight Japanese laboratories

A control survey was conducted to check the accuracy of automated analyzers used in the evaluation of clinical chemistry parameters in nonclinical toxicology studies. Pooled serum samples from male Sprague-Dawley rats were delivered refrigerated to each facility 98 laboratory facilities throughout Japan within 18 hours after sample preparation and analyzed. Commercially available normal human serum samples from a single lot were also analyzed at the same time. Survey results were divided into three categories. (1) Parameters with small coefficient of variation (CV) values for both rat and human serum samples included protein, glucose, cholesterol (CHO), urea nitrogen (UN), sodium (Na), potassium (K), chloride (Cl), calcium (Ca), and inorganic phosphate (IP). Definition of normal values in rats should be straight forward for these parameters. (2) Parameters with large CV values, but with a relatively good correlation between rat and human values include triglycerides (TG), glutamic oxaloacetic transaminase/aspartate aminotransferase (GOT/AST), glutamic pyruvic transaminase/alanine aminotransferase (GPT/ALT), and alkaline phosphatase (ALP). Measurements based on different principles gave different mean values, and this values contributed to the increase in CV values. Assessment of normal values would require a consideration of the measurement principles. (3) Parameters with large CV values only in rat serum samples included albumin (albumin/globulin ratio: A/G ratio), creatinine (CRE), and total bilirubin(BIL). Reactivity was different in rat albumin (ALB), depending on the reagents used. This difference needs to be corrected with values available by electrophoresis, or adjusted by rat ALB values, because of the lack of an appropriate measurement method. The enzyme method gave low values for rat CRE, which suggests the need for further examination of this method. The BIL values were extremely low in rat samples. It seems to be necessary to select appropriate methods to measure clinical pathology parameters correctly for rats. There was no deviation in values due solely to the mechanical operations of the analytical equipment. Non-standard initial settings of the equipment (equipment originally intended for human samples, but now applied to animal samples) was the main cause of the wide range of analytical values seen.

The measurement of bilirubin fractions in serum

Bilirubin fractions are measured by (1) the direct diazo reaction, (2) high-performance liquid chromatography (HPLC), (3) direct spectrophotometry, and (4) enzymatic methods. HPLC, which effects separation and quantitation of the four bilirubin fractions, is the method of choice, but impractical for routine use. A special application of direct spectrophotometry allows the measurement of unconjugated bilirubin and the sum of bilirubin conjugates. This approach, which provides essentially the same information as HPLC, unfortunately is available only in one clinical analyzer. The direct diazo reaction measures bilirubin conjugates plus delta-bilirubin, albeit not very accurately. Direct diazo methods that measure unconjugated bilirubin as direct could obscure the clinical diagnosis. At acid pH, enzymatic methods measure all direct reacting bilirubins, while at pH 10 only conjugated bilirubins are measured. Because the measurement of conjugated bilirubins is clearly more helpful than that of direct bilirubin in the differential diagnosis of jaundice, direct diazo methods should be replaced by methods specific for bilirubin conjugates.

Molar absorptivities of bilirubin (NIST SRM 916a) and its neutral and alkaline azopigments

Three laboratories in the U.S. and two in the Netherlands determined molar absorptivities (epsilon) of Standard Reference Material (SRM) 916a Bilirubin from the National Institute of Standards and Technology. In caffeine reagent the average epsilon values were 50,060 and 48, 980 L.mol-1.cm-1 at 432 and 457 nm, respectively. The epsilon value of the blue azopigment, obtained with the Reference Method for total serum bilirubin, was 76,490 L.mol-1.cm-1 at 598 nm. When the addition of alkaline tartrate was omitted, the molar absorptivity of the red azopigment was 56,600 L.mol-1.cm-1 at 530 nm.

Light has a greater effect on direct bilirubin measured by the bilirubin oxidase method than by the diazo method

We compared the effect of light on direct-reacting bilirubin (DBIL) measurement by the bilirubin oxidase (EC 1.3.3.5; BOX) method and by the Jendrassik-Gróf diazo method. DBIL concentrations determined by the BOX method in the sera of hyperbilirubinemic infants treated with phototherapy yielded falsely higher values than those by the direct diazo method. A similar tendency was noted when DBIL concentrations in infants' sera irradiated with light in vitro were determined by both methods, although by HPLC none of these sera had detectable DBIL (i.e., conjugated plus delta bilirubin). In general, DBIL concentrations after photoirradiation remained unchanged when measured by the diazo method, but significantly increased when the BOX method was used. Indeed, photoirradiation gave rise to material that acted like a photobilirubin product, which was oxidized at pH 3.7 and therefore was measured as DBIL. Such false increases in DBIL values generated by the BOX method may have clinical diagnostic implications in monitoring jaundiced neonates and in differentiating between physiological jaundice and incipient pathological jaundice.

Total and direct-reacting bilirubin values by automated methods compared with liquid chromatography and with manual methods for determining delta bilirubin

This study compares total and direct-reacting bilirubin values in 40 serum samples from patients with various diagnoses, as measured by automated methods (Beckman Synchron CX-5, Beckman Astra 8, Kodak Ektachem 700) and HPLC and by a manual method for delta bilirubin. For total bilirubin, within-run CVs were less than 6%. The Ektachem 700 method underestimated bilirubin with serum samples from patients with Crigler-Najjar syndrome and from newborns in whom unconjugated bilirubin concentrations were increased but conjugated bilirubins were not present or were present only in small amounts. The Astra 8 and Synchron CX-5 methods were inaccurate with cholestatic serum samples, in which conjugated bilirubin concentrations were increased and other compounds such as bile acids could be expected to interfere. We conclude that each automated method examined provides reasonable estimates for total and direct-reacting bilirubin values for routine clinical use. The need for each laboratory to select the appropriate bilirubin method for its particular situation is obvious.

Three direct spectrophotometric methods for determination of total bilirubin in neonatal and adult serum, adapted to the Technicon RA-1000 analyzer

We adapted three bichromatic spectrophotometric methods for determining total bilirubin in serum, for use with the Technicon RA-1000 analyzer. The borate buffer (BOR) of Hertz et al. (Scand J Clin Invest 1974;33:215-30), the caffeine buffer (CAF) of Vink et al. (Clin Chem 1988;34:67-70), and the combined borate-caffeine buffer (B-C) of Franzini and Cattozzo (Clin Chem 1987;33:597-9) were compared. All methods required only 10 microL of serum, were precise (between-batch CVs less than 4.2%, analyte range 64-310 mumol/L), linear to 1000 mumol/L, and insensitive to interference from hemoglobin to 5 g/L. Lipemia, carotene, and methemalbumin interfered positively with each method but insignificantly unless in supranormal concentrations. Only the BOR method was sensitive to protein matrix effect. Neonates' results obtained with all three methods compared well with a Jendrassik-Gróf-based technique. However, samples from adults with cholestasis were overestimated, particularly by the CAF method, but the BOR and B-C methods would be suitable for "stat" bilirubin analysis in these samples.

Use of the caffeine reagent in direct spectrophotometry of bilirubin

The molar absorptivity of unconjugated bilirubin in caffeine reagent is independent of the protein matrix. This finding, together with the simplicity of a dilution step for direct spectrophotometry, will improve the calibration methods of bilirubin and make them more nearly accurate. This is encouraging for the development of a new method for bilirubin determination in neonates; moreover, the caffeine reagent has a clearing influence on the turbidity of human sera. These findings should also be important for standardization, especially because the method of Jendrassik and Gróf is also protein-independent. Therefore, the introduction of one reliable, inexpensive, "universal" standard of bilirubin in bovine serum albumin will be of importance for both methods.

Candidate reference method for determination of total bilirubin in serum: development and validation

This candidate Reference Method for measuring total bilirubin in serum is based on the Jendrassik-Gróf principle (Clin Chem 29: 297-301, 1983). Standard Reference Material no. 916 bilirubin (National Bureau of Standards) is used as the standard. Bilirubin standard solutions may be prepared either in human serum or in 40 g/L albumin solution (human or bovine), because we found the molar absorptivity of the azopigment at 598 nm to be identical in these media. The absorptivities of the unconjugated and conjugated azopigments appear to be identical, but the conjugated azopigment is completely hydrolyzed in the final reaction mixture. Bilirubin added to serum from adults or neonates was quantitatively accounted for. Interference by hemoglobin (up to 2 g/L), ascorbic acid (up to 20 mg/L), or zinc (at physiological concentrations) is negligible. Of the therapeutic drugs we tested, only L-dopa and alpha-methyldopa interfere. We established normal adult reference values for total bilirubin and examined the intraindividual variation in 19 subjects.

An improved freeze-dried bilirubin preparation

We describe the conditions for successful freeze-drying of bilirubin solutions in the presence of dimethylsulfoxide and human serum albumin. Freeze-dried bilirubin preparations rehydrate readily, rapidly resulting in clear solutions. The preparations exhibit excellent homogeneity and stability at -20 degrees C. Accelerated storage tests indicate that the freeze-dried product would also be stable at higher temperatures but our results do not permit, at the present time, to make accurate predictions regarding the stability at 4 degrees C or 0 degrees C. We believe that our approach will permit manufacturers of bilirubin calibrators for clinical use to improve the quality of their products.