HORMONAL IMMUNOASSAYS

COMPARISON USING ECL & ELFA

Abstract

Objectives: several improvements have been made in the design of immunoassays
such as method of antibody production, labeling, automation and detection technology. The aim of
the present study was to compare the accuracy and precision of enzyme linked immunofloriscence
assay (ELFA) and electrochemiluminescence assay (ECL), with Elisa for determination of serum TSH
levels. Period: Feb 2014 to Nov 2014. Setting: College of postgraduate studies, University of Al-
Neelain, Khartoum, Sudan. Material and Methods: Three commercial control materials low, normal
and high levels of TSH, were used for imprecision studies of immunofloriscence assay (ELFA) and
electrochemiluminescence assay (ECL) methods and 120 patients samples including low (20%),
normal (50%), and high (30%) TSH levels, were measured by the two methods, and used for methods
comparison. In addition to six assigned prepared pool serum used for linearity evaluation of the two
methods. Results: Inter- and intra-assay CV% for ECL and ELFA was significantly low compared with
the required by the manufacture. (Intraassay CV% for ECL was 2.9%, 2.74%, and 2.55% for low,
normal, and high respectively of TSH levels of the control sera. Intraassay CV% for ELFA was 3.95%,
3.75%, and 5.73% for low, normal, and high respectively of TSH levels of the control sera. Interassay
CV% for ECL was 3.0%, 2.75%, and 2.81% for low, normal, and high respectively of TSH levels of
the control sera. Intraassay CV% for ELFA was 4.26%, 4.0% , and 5.75% for low, normal , and high
respectively of TSH levels of the control sera. Although the mean TSH levels of the three levels of the
control sera measured by ECL & ELFA methods, is significantly difference from assigned TSH mean
values( low 0.488+/-0.078,normal 6.016+/- 0.952,high 33.651+/-5.39) , but the measured values is
within the mean range of the assigned means values. ECL; low (0.611 +/- 0.018. p ≤ 0.001), normal
(6.6785 +/- 0.183. p ≤ 0.00), high (35.0485 +/- 0.894. p ≤ 0.02). ELFA low (0.50545 +/- 0.020. p ≤
0.00) , normal (6.5395 +/- 0.244. p ≤ 0.00), high (31.0350 +/- 1.779. p ≤0.001).The mean TSH levels
of the 120 patients samples measured by ECL & ELFA , is significantly difference , for ECL (15.74+/-
1.181 . p ≤ 0.00) when compared with the mean TSH value (14.56 +/- 1.65) of the patients samples.
For ELFA method also there is significant difference (13.76 +/- 1.59 , p ≤ 0.00) when compared
with mean of the assigned TSH values(14.56 +/- 1.65) of the patients samples, but within the target
values of the means .The study showed strong relationship between the two TSH levels measured
by ECL( mean 15.74 mIU/L, slope 0.67 , correlation coefficients 0.991, p ≤ 0.00) and by ELFA (
mean 13.76 mIU/L, slope 0.54, correlation coefficients 0.995, p ≤ 0.00) with the assigned values
(14.56 ) of 120 patients sample .The results illustrates no significant difference of TSH mean level in
six prepared pool samples measured by ECL(22.63 mIU/l +/- 1.12 , p ≤ 0.1) and ELFA(19.87mIU/l
+/- 1.15 , p ≤ 0.11) when compared with the TSH assigned values(22.54 mIU/l +/-0.96), and with
strong correlation between the two TSH levels measured by ECL(22.63 mIU/l, slope 0.79, correlation
coefficients 0.999, p ≤ 0.00) and ELFA ( mean 19.87mIU, slope 0.68, correlation coefficients 0.985,
p ≤ 0.00), with the assigned TSH values (22.54 mIU/l +/-0.96).of the six prepared pool samples.
Conclusion: Considerable significant precision and accuracy was manifested by both ECL and ELFA
methods in estimation of TSH levels, but ECL is more precise than ELFA especially in the lower TSH
concentration.