Abstract:
Background: Tumour markers are produced in the body on cancers and quantified in
laboratories for diagnosis of malignancies. If concentrations of markers lie beyond the
analytical ranges, dilutions are performed. The dilutional linearity, the deviation of
concentrations by dilutions, indicates the accuracy and it should be excellent to obtain readings
of dilutions as analyte concentrations. The dilutions are performed in small dilution factors
instead of maximum dilution factors (MDFs) which give high accuracy by diluting interfering
substances. But the use of MDFs requires a high volume of diluents. Therefore, the
determination of MDFs and cost-effective alternative diluents are important for routine
laboratory settings.
Objectives: To assess dilutional linearities and define MDFs for selected six tumour markers
using commercial diluents and pooled human serum on automated platforms
Methods: The requests received to Teaching Hospital-Karapitiya within 3 months (October December, 2019) were counted to find the number of dilution-required samples. Retained
samples (n = 7 per marker) with high concentrations of analyte [Carbohydrate Antigen 125
(CA-125), Prostate-Specific Antigen (PSA), Ferritin, Thyroglobulin (TG), Alpha-fetoprotein
(AFP) and β-Human Chorionic Gonadotropin (β-HCG)] were diluted as 1:10,1:20,1:50,1:100
and 1:200 using commercial diluents and in-house prepared serum pool and analyzed in
automated analyzers (Snibe Maglumi 1000 and Vitros 3600 analyzers). Non-parametric and
recovery studies were performed.
Results: The 5-15% of received samples were required dilutions within 3 months. The
Kendall’s coefficients were nearby 1 (0.921-0.995), illustrating satisfied dilutional linearities
of assays. There were no significant differences (p >0.05) among results generated by diluents
and pooled serum. The acceptable MDFs were defined by considering “mean recovery
percentages” and “p-values”. The acceptable MDFs for β-HCG, AFP, TG, ferritin and CA-125
were 1:50, 1:20, 1:50, 1:20 and 1:20 respectively in commercial diluents. The acceptable
MDFs for β-HCG, AFP, PSA, TG, ferritin and CA-125 were 1:50, 1:200, 1:200, 1:50, 1:100
and 1:100 respectively in pooled serum.
Conclusions: The pooled serum can be used with high MDFs as 1:200 for assays of serum
AFP and PSA and 1:100 for serum ferritin and CA-125. The pooled serum is more preferable
for maximum dilutions due to cost-effectiveness.
