HBA® test is a functional test extending seminological diagnostics. It leads to the choice of an appropriate assisted reproduction technique, which translates into a higher probability of pregnancy. The HBA test allows to determine the ability of sperm cells to bind to hyaluronate (hyaluronic acid) and thus it determines the percentage of sperm cells that are capable of fertilizing the egg cell.
What does HBA® test check?
The primary purpose of the HBA® test is to determine the maturity of sperm cells in fresh semen. This is possible due to the binding of mature sperm with hyaluronate. HBA means hyaluronan binding assay.
The importance of hyaluronate in the fertilisation process
- Hyaluronate is a substance that plays an important role in the interaction between sperm cells and the egg cell. This interaction, if it goes well, leads to fertilization. In natural conditions, hyaluronate occurs in the extracellular matrix of the cumulus oophorus surrounding the egg cell and is abundantly secreted by the granular cells of the cumulus oophorus.
- In the final stage of spermatogenesis (sperm cells maturing process), special spots are formed on the surface of the sperm heads, which bind to the hyaluronate and the zona pellucida of the egg cell. The presence of these spots is essential in the process of the sperm head binding to the surface of the zona pellucida of the egg cell during the fertilization process taking place in the female reproductive tract.
- Sperm cells on the surface of which no such spots have developed are not able to bind to the hyaluronate and therefore are not able to bind to the surface of the zona pellucida of the egg cell either naturally or during in vitro fertilisation using the classic IVF method. The lack of binding to the hyaluronate leads to a lack of fertilization.
▪ extended semen testing, the results of which are within the range of normal or show slight deviations from the strange of normal,
▪ the need for supplementary diagnostics of male fertility disorders,
▪ recurrent miscarriages,
▪ SCD, MSOME test results out of the range of normal,
▪ infertility of unknown cause (idiopathic infertility).
Therefore, the HBA® test cannot be performed in patients diagnosed with:
▪ severe asthenozoospermia (a significant lowering of sperm cells motility in the semen),
▪ necrospermia (all sperm cells without motility, dead).
Preparation of a patient for a HBA test
This test does not require special preparation from the patient. In order for the embryological team to perform the HBA test, the patient should provide a semen sample according to the rules that apply to other semen tests - with 3 to 5 days of sexual abstinence and abstinence from the consumption of alcohol and other stimulants for a minimum of 5 days before the test.
How is a HBA test performed?
For this test, microscopic slides coated with hyaluronic acid are used, onto which a sample of fresh semen is placed by a laboratory employee. Then, after several minutes, the specimen is viewed under a light microscope. At least 100 motile sperm cells, both those that have bound to the hyaluronate on the slide and those that have not, shall be counted and the percentage of mature (bound) sperm in the test sample shall be calculated.
HBA test result
The interpretation of a specific HBA test result depends on the reference values given by the test manufacturer and should be specified in the result.
An increased percentage of sperm cells that do not bind to hyaluronate i.e. immature sperm cells or with abnormal hyaluronate-binding spots, means the limited ability or inability of the sperm cells to fertilise the egg cell, and their use in the classical IVF procedure may lead to a lack of fertilisation.
The HBA result is significantly correlated with the quality of the embryos, the miscarriage rate and the rate of developing pregnancies in fresh cycles (in cycles where fresh embryos were used).
In patients with normal semen parameters, both in the extended and HBA® testing, classical egg cell insemination (IVF) or intracytoplasmic sperm injection (ICSI) is possible.
▪ ICSI, which consists in the intracytoplasmic injection of a sperm cell into an egg cell.
▪ PICSI®, i.e. the so-called physiological ICSI. This is an ICSI procedure in which, in addition, sperm cells which are able to bind to hyaluronic acid are selected for injection.
Source: Clinical benefit using sperm hyaluronic acid binding technique in ICSI cycles: a systematic review and meta-analysis, Ronit Beck-Fruchter, Eliezer Shalev, Amir Weiss. Reproductive BioMedicine Online (2016) 32, 286-298; URL: https://www.ncbi.nlm.nih.gov/pubmed/26776822).
Clinical tests results
Recent multi-center, double-blind, randomized clinical trials using semen selected in the HBA or PICSI tests gave the following results:
- embryos with less DNA fragmentation,
- a higher percentage of embryos maturing to a blastocyst stage,
- a higher rate of clinical pregnancies,
- lower miscarriage rate.
Recent research by Japanese scientists has confirmed that HBA-ICSI (ICSI preceded by selection of spermatozoa on the basis of hyaluronate binding) shows a higher proportion of high quality blastocysts compared to ICSI trials without HBA selection that were undertaken in the same patients. Obtaining higher quality blastocysts goes hand in hand with a higher percentage of clinical pregnancies.
Source: The Evaluation of Sperm’s Hyaluronic Acid Binding Ability as a Predictive Value for the Clinical Success of Intracytoplasmic Sperm Injection, Bulletin of the Osaka Medical College 65 (1,2): 1-6, 2019; URL: https://www.osaka-med.ac.jp/deps/b-omc/articles/65/65igawa.pdf).