AFP Allotype - Lectin Binding Index, Fucosylation Index, Yolk Sac AFP

Immunology

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Description

Alpha-fetoprotein (AFP) is a single-chain glycoprotein with a molecular mass of approximately 67,500 daltons. AFP shares considerable sequence homology with albumin, and is produced by the foetus primarily in cells of the yolk sac, gastrointestinal tract and liver. AFP appears as a major serum protein in the foetus, but its concentration decreases rapidly toward birth. When embryonic haemopoiesis is replaced by foetal haematopoiesis, the synthesis of AFP is transferred to the liver [2]. Serum AFP levels can be raised in both malignant and benign liver disease. Therefore is of little use in providing a differential diagnosis [1]. The AFP isotypes produced in cells from different organs and under various pathological conditions are immunologically the same, but a difference exists in the degree of fucosylation of AFP between hepatocellular carcinoma and gonadal tumours. This is due to the different tissue specific pathways that are involved. This microheterogeneity is displayed by AFP isotype reactions to different lectins. The lectin, Concanavalin-A (Con-A), can be used to separated the isoforms of AFP that are of yolk sac and liver origin [2]. In sera from patients with hepatocellular carcinoma (HCC) the ratio of Con-A lectin-reactive AFP significantly increases [1]. The fucosylation index, also referred to as the lectin-binding index, can be calculated in cases of extremely raised AFP levels in order to distinguish the tissue origin [1]. Tumours of yolk sac origin will give a greater % for the lectin-binding index, as yolk sac AFP does not bind well to Con-A lectin, therefore is not removed upon pre-treatment with it. AFP of liver origin will react with Con-A, giving a lower lectin-binding index result.

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Indications

To differentiate the Alpha-fetoprotein (AFP) produced by hepatocellular carcinoma from gonadal/extragonadal tumours (AFP of yolk sac origin) or from benign liver disease.

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Sample Type

2mL Serum (Gel 5mL Yellow tube). Requests from outside Sheffield: Transport at ambient temperature via Royal Mail or Courier.

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Reference Range

See report.Reference range established in 1986 by Chan DW, et al.

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Turnaround Time

Within 5 days

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Testing Frequency

As required

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References

Blomme et al. Alteration of protein glycosylation in liver diseases. Journal of Hepatology. 2009. 50:592-603. [Ref 1]Gerald J and Mizejewski. Alpha-fetoprotein Structure and Function: Relevance to Isoforms, Epitopes, and Conformational Variants. Experimental Biology and Medicine. 2001. 226:377-408. [Ref 2]Mora J, et al. Alpha-fetoprotein-concanavalin A binding as a marker to discriminate between germ cell tumours and liver diseases. Eur J Cancer. 1995. 31A(13-14):2239-2242.

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