Dear kindly check the convertion factor on the manual of the kit.

Article International reference preparation for human serum IgG, IgA, IgM

Dear Paniz, that online converter does not include antibodies, do you know another tool?

@Emmanuel Ifeanyi Obeagu we are not using a kit (so there is no manual), only the anti-Hepatitis B antibody from the pharmacy, and the package/package insert doesn't state any conversion factor.

Dear Ruby, with the information provided by Orwa Barakat and assuming that your Hepabig preparation has IgG, the concentration of 100 IU/0.5 mL (or 200 IU/mL which is the same) equals 16.1 mg/mL with three significant numbers.

In the attached file I present a simple Excel sheet to make the conversion with any of the memory antibodies (IgG, IgA or IgE) and from any concentration in IU/mL.

José Luis Duque-Rivera are you sure this is the right way to convert the units? I am asking because despite an intensive search over the last weeks I didn't find other sources for the conversion factor for anti-HBsAg antibodies.

There are four subclasses of human IgG with different molecular mass: IgG1 = IgG2 = IgG4 = 146 kDa, IgG3 = 170 kDa (see for example Article IgG Subclasses and Allotypes: From Structure to Effector Functions

Dear Maciej Jacek Swat , there seems to be very little information available in this regard. The calculations that I proposed in the Conveter file (attached in a previous message in this same discussion thread) are based on the equivalences of the article by Humphrey and Batty I. (1974, Clin exp Immunol 17: 708). Given that more than 40 years have passed, it could be thought that there are updates on these equivalences.

Maciej Jacek Swat , the paper you cited (doi: 10.3389 / fimmu.2014.00520) is an interesting review on IgG. Judging by the molecular masses (currently it is recommended to use the phrase "molar mass") according to that indicated by the paper, a pharmaceutical preparation can have a weighted molecular mass (MMw) that will depend on the proportion of the sublcase IgG3. That MMw will influence the conversion factor, that is, the mass / IU equivalence.

Maciej Jacek Swat , you say that "the composiiton of the anti-HBsAg IgG changes with age and disease status" and I agree, but since it is a pharmaceutical preparation, which is the case raised by Ruby Anne King, its production must be a standardized process from a pool and the composition must be relatively stable over time. However, any change in production batches in the proportion of IgG3, if this subclass is present in the formulation, should affect the conversion factor.

Maciej Jacek Swat , a pending task is to find out what is the definition of "international unit" for IgG immunoglobulins. By the way, the review paper indicates that the relative abundance of igG3 is 4% (see Table 1). The most important subclasses are IgG1 (60%) and IgG2 (32%) and IgG4 has 4% as well. If we assume these proportions in a pharmaceutical preparation, the weighted molecular mass (MMw) would be 146.96 kDa. The presence of only 4% of IgG3 of 170 kDa, only increases the MMw by one point with respect to the molar masses of the other subclasses (146 kDa).

José Luis Duque-Rivera thanks for the discussion, very useful. Regarding subclasses distribution in connection with HBV, the following paper is very insightful, Article IgG subclass composition of antibodies to HBsAg in circulati...

Dear Maciej Jacek Swat, I have traced the information of the mass / IU equivalence of IgGs to the following papers:

Paper 1:

Rowe DS, Anderson SG, Grab B. A research standard for human serum immunoglobulins IgG, IgA and IgM. Bull World Health Organ. 1970;42(4):535-552.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2427461/pdf/bullwho00215-0038.pdf

Paper 2:

Rowe DS, Grab B, Anderson SG. An international reference preparation for human serum immunoglobulins G, A and M: content of immunoglobulins by weight. Bull World Health Organ. 1972;46(1):67-79.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2480623/pdf/bullwho00188-0080.pdf

I summarize the aspects that I consider key:

1) The 80 ug / IU equivalence for IgG arises from an international reference preparation made by the Division of Biological Standards of the National Institute of Medical Research in London and from an international collaborative study sponsored by the WHO. The preparation consists of a cold-dried antibody powder (standard ampoule) that is reconstituted in 1 mL of distilled water.

2) The content of the standard ampoule resulted from a pool made with 761 healthy donor individuals in 1967 with no history of malaria or hepatitis. So the IgG subclass composition of this ampoule does not reflect the composition of these antibodies due to the immune system's reaction to acute or chronic Hepatitis infections.

3) The content of the standard ampoule is arbitrarily set to equal 100 IU for IgG, 100 IU for IgA and 100 IU for IgM. The equivalences are obtained from the data in Tables 6 and 7 of Paper 2. These are the relevant data:

IgG: 7.59 mg/mL; 94.4 IU/mL.

IgA: 1.34 mg/mL; 94.4 IU/mL

IgM: 0.80 mg/mL; 94.4 IU/mL

4) The calculations are as follows:

Mass/IU equivalence (IgG) = (7.59 mg/mL x 1000 ug/1mg) / 94.4 IU/mL = 80.4 ug/IU

Mass/IU equivalence (IgA) = (1.34 mg/mL x 1000 ug/1mg) / 94.4 IU/mL = 14.2 ug/IU

Mass/IU equivalence (IgM) = (0.08 mg/mL x 1000 ug/1mg) / 94.4 IU/mL = 8.47 ug/IU

José Luis Duque-Rivera thanks for the detailed analysis. Yes, I am aware of the papers. You might be interested what I found wrt anti-HBsAg antibody. Stamm et al. measured its binding capacity to HBsAg

Article Quantitative determination of antibody against hepatitis B s...

That allows to calculate the IU for mass of anti-HBsAg antibodies (ignoring subclasses, assuming average MM=150kDa for IgG). From my calculation it follows that 1IU of anti-HBsAg antibodies corresponds to 2.67 and 5.35 micro*g, for 2:1 and 1:1 binding, respectively (IgG has 2 binding sites). Let me know if you agree with that results.

Edit: see the comments by the second author of the Stamm et al. paper in this discussion https://www.researchgate.net/post/How_do_you_really_convert_serum_HBsAg_measured_in_ng_ml_to_iu_ml

Dear Maciej Jacek Swat , I do not understand the results you have reported. If it's not much of a hassle, could you please present the detailed calculation?

José Luis Duque-Rivera It is really basic algebra but the key point is to realise that IgG has two binding sites. In the calculation I assume the two extreme cases, that all IgG molecules bind one or two HBsAg. In reality a mixture of these is most likely the case but I have no data on that. Do you know anything about it?

The binding activity is according to Stamm et al. 1980 given as: 1 IU of IgG binds to 0.906E-6 g of HBsAg. Below a simple algorithm to calculate the IU SI units equivalence (Avogadro number, N = 6.022E23):

Step 1: Molecular mass of HBsAg = 25421 g/mol

Mass of 1 molecule of HBsAg, M_1HBsAg = 25421 / N

Average molecular mass of IgG is 150,000 g/mol

Mass of 1 molecule of IgG: M_1IgG = 150000 / N

Step 2: Number of HBsAg molecules bound by 1 IU of IgG

numOf_HBsAg = 0.906E-6 / M_1HBsAg

Step 3: Number of IgG molecules in 1 IU for 1:1 binding:

numOf_IgG_1to1 = numOf_HBsAg

Number of IgG molecules in 1 IU for 2:1 binding:

numOf_IgG_2to1 = numOf_HBsAg / 2

Step 4: Mass of 1IU of IgG for 1:1 and 2:1 binding:

M_1IU_IgG_1to1 = numOf_IgG_1to1 * M_1IgG

M_1IU_IgG_2to1 = numOf_IgG_2to1 * M_1IgG

That gives the interval [2.672987, 5.345974] micro*g of IgG equivalent to 1 IU.