ABSTRACT
Sweat chloride (Cl(-)) measurement is a key step for the diagnosis of cystic fibrosis. The coulometric technique is validated in this context by international guidelines. The aim of our study was to evaluate the assay for sweat Cl(-) ions using direct potentiometry on disposable cassette (Spotchem™ SE EL-1520, Elitech-Arkray) by comparing results to those obtained on the same sample, by coulometry (Chloride analyser Sherwood 926S, Dutscher). To complete our table of correspondence between the results of Cl(-) ions and sweat conductivity (Sweat Check™ 3100), conductivity has been also achieved for 99 of the 139 sweat samples studied. Linearity of each technique performed extends from 10 to 120 mmol/L. The coefficients of variation within and between runs are < 5%. Comparison of 139 results (Passing - Bablock regression) shows a significant difference (p < 0.001): [Spotchem] = 1.026 [Chloride analyser] + 1.8, r = 0.996. After correction with regression factors, only 6 pairs of values (4.6%) had a difference greater than ± 5 mmol/L). The results of conductivity measurement is strongly correlated with those of Cl(-) ions (r = 0.959 for Chloride analyser and 0.965 for Spotchem; p = 0.576) with a linear relationship between the decision thresholds from 30 to 60 mmol/L Cl(-). Sweat Cl(-) determinations using Spotchem™ analyser meet the criteria required by analytical recommendations. The technique is standardized, easy to perform and fast. Its good practicability makes the sweat test independent to operator and allows point-of care use.
Subject(s)
Chlorides/analysis , Potentiometry/methods , Sweat/chemistry , Adolescent , Adult , Aged , Child , Child, Preschool , Cystic Fibrosis/diagnosis , Electric Conductivity , Electrolysis/instrumentation , Electrolysis/methods , Humans , Infant , Ion-Selective Electrodes , Middle Aged , Muscarinic Agonists , Pilocarpine , Potentiometry/instrumentation , Young AdultABSTRACT
Sweat test measuring the chloride ion (Cl(-)) concentration in sweat is a tool for the cystic fibrosis (CF) diagnosis. We evaluated analytical criteria of different available methods and compared them into five hospitals and throught a national quality control program. Sweat tests were performed by stimulation using pilocarpine iontophoresis, sweat collection and measurement of sweat Cl(-) (mmol/L) by titration (colorimetric or coulometric end-point) or by in situ direct potentiometry using a chloride-selective electrode. Indirect determination by sweat conductivity measurement was expressed in mmol/L sodium chloride (NaCl) equivalents (Eq). Linearity range was demonstrated for all measurement procedures in the range 10 to 120 mmol/L. Intra-laboratory coefficients of variation (CVs) were <5% for values between 10 and 100 mmol/L. Inter-laboratory CVs were <3% only for conductivity measurement whatever the range. The comparison of results obtained for a same sweat sample, simultaneously by coulometric and conductivity measurements, demonstrated a first degree linear distribution between 30 to 60 mmol/L Cl(-) allowing us to establish an analytical correspondence table for this range. Thus, calculated values for 30, 40 and 60 mmol/L Cl(-) were respectively 57, 66 and 84 mmol/L NaCl Eq. In conclusion, comparison of methods highlighted that the less the sweat test is automatically controlled, the more the operator influence on results quality is important. Our study supports that sweat test result <50 mmol/L NaCl Eq is unlikely with CF diagnosis in absence of clinical arguments.
Subject(s)
Biological Assay/methods , Biological Assay/standards , Diagnostic Techniques, Endocrine/standards , Sweat/chemistry , Biosensing Techniques/methods , Child , Child, Preschool , Electric Stimulation/methods , Electrophysiological Phenomena , Female , Humans , Infant , Infant, Newborn , Male , Quality Control , Retrospective Studies , Sensitivity and Specificity , Sweat/metabolism , Sweat/physiologyABSTRACT
BACKGROUND: Jaundice is frequent in neonates and can cause severe complications, especially in premature neonates, particularly the risk of developing acute bilirubin encephalopathy. Our purpose was to verify if determination of total bilirubin (TBIL) in whole blood on an ABL 735 blood gas analyzer with a spectrophotometer module could provide an analytical alternative to chemical methods of TBIL measurement. METHODS: Our multicenter comparative study involved four hospital laboratories. We studied the repeatability and reproducibility of ABL 735 TBIL measurements in two control sera of medium (N1, 58.1 micromol/L) and high (N2, 275.3 micromol/L) TBIL levels. The same study was simultaneously conducted on four chemistry instruments (two LX 20, one Integra 800 and one Hitachi 917) using four Jendrassik-Grof derived methods. At one site, repeatability was performed with two adult whole-blood samples containing low and high TBIL levels (55.1 and 312.6 micromol/L). RESULTS: Repeatability tests provided coefficients of variation (CVs) between 0.67% and 1.86% on the ABL 735 system, vs. 0.35% and 1.96% for the chemistry instruments. Reproducibility tests for the same control sera resulted in CVs between 1.01% and 3.55% for the ABL 735 and between 0.52% and 3.65% for the chemistry instruments. Recovery for the N1 and N2 control sera was 102-120%. A correlation study of TBIL determination in whole blood vs. plasma was conducted on 473 neonatal blood samples. Correlation coefficients between whole blood and plasma TBIL ranged from 0.969 to 0.994. Passing-Bablok equations were y=1.17x+9.7 [site 1 (IP)], y=1.01x+5.6 [site 2 (JPB, MR)], and y=1.00x-20 [site 3 (AS)]. Only 10% of the results fell outside the 10% range in the bias-corrected Bland-Altman difference plot for the ABL 735 method compared to traditional laboratory methods. CONCLUSIONS: The ABL 735 instrument is reliable for measuring TBIL in 70-microL whole blood samples from neonates. Thus, this method might allow significant blood savings in preterm neonates. Correlation with the reference method for plasma or sera must be established to ensure good follow-up of patients.
