JP3220378B2 - Method and reagent for quantification of total protein - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method and a reagent for quantifying total protein which is hardly affected by interfering substances. More particularly, the present invention relates to a method and a reagent for quantifying total protein which is hardly affected by an interfering substance in a sample mainly used in the field of clinical examination.

[0002]

2. Description of the Related Art As a method for determining total protein, a refractometer method,
There are a method based on specific absorption at 280 nm, a turbidimetric method, a Kjeldahl method, a biuret method in which a peptide bond is bound to copper with alkali and colorimetrically performed, and the like. In particular, the biuret method has a constant color development sensitivity irrespective of the type of protein and can be easily colorimetrically determined. Although the biuret method has a drawback of low sensitivity, it is rather convenient for quantifying total protein in serum, and has been widely used in clinical tests.

[0003] The reaction principle of the biuret method is based on the fact that copper forms a complex with a peptide bond of a protein under alkaline conditions, thereby producing a reddish purple color (around 550 nm). The color development is compared with the absorbance of the standard solution to quantify the amount of protein in the sample. A chelating agent may be added to prevent precipitation of copper hydroxide under alkaline conditions, and potassium iodide may be added to prevent copper from being reduced.

[0004] However, these methods have a problem of turbidity of the specimen due to, for example, chyle, hemolysis, bilirubin, etc., which are often encountered in daily tests, that is, interference by coexisting substances. In the past, there have been several reports on the biuret method regarding interference avoidance methods, all of which are reports on chelating agents, reports on methods to avoid turbidity due to dextran used mainly for infusion, and other reagents that do not contain copper And blinded samples such as chyle and hemolysin (Doumas et al., Clin. Chem. 27/10, 1642-
1650, 1981). In the method of Doumas et al., One type of solution containing 12 mM copper sulfate, 32 mM sodium potassium tartrate, 30 mM potassium iodide, and 0.6 M sodium hydroxide is used.

A recent automatic analyzer divides the reagent into two reagents (two-reagent system) to measure the absorbance in the first reagent and to perform the reaction after the addition of the second reagent to measure the absorbance again.
The mainstream is two-point measurement in which a target substance is quantified from a difference in absorbance. According to this method, it is said that the color and turbidity of the specimen can be subtracted, so that more accurate measurement can be performed.

[0006] Although quantification of total protein has been performed for a long time, it is regarded as an item most susceptible to interference in current biochemistry tests of clinical chemistry. The biggest reason is that only one point can be measured because it is a system for reacting and measuring with one reagent (one reagent system). Most of the total protein quantification reagents on the market are single reagents and cannot avoid interference, but only DuPont aca
Test pack total protein TP (in vitro diagnostic drug (01AM))
No. 0015) is divided into two reagents. This reagent has a structure in which sodium hydroxide is contained in the first reagent and copper sulfate is contained in the second reagent. First, sodium hydroxide is added, and then copper sulfate is added, and the reaction is measured. In this case, there is no need to perform sample blinding, and interference from chyle and hemolysis can be avoided, but interference from bilirubin cannot be avoided. This is because the bilirubin in the sample is rapidly changed to biliverdin when copper ions are added, and negative interference occurs when the sub-wavelength is set to around 700 nm (Clinical Chemistry (20) Supplement No. 2) 51b (1991)). At present, no method has been found to completely avoid bilirubin interference.
In the method of adding the solution containing copper ions as the second reagent later, the absorbance around 700 nm which is the secondary wavelength is high, and the measured value is easily affected by the dispensing accuracy of the second reagent. Reproducibility deteriorates.

The biuret method is also affected by endogenous substances such as amino acids, sugars and creatinine, and drugs such as dextran and bromosulfalene (BSP). BSP
Is used in a dye absorption tolerance test as one of liver function tests, and has a maximum absorption at a wavelength of 580 nm under alkaline conditions. Therefore, it was said that the sample collected after the stress test could not be quantified by Biuret reagent for total protein.

It is also believed that amino acids, sugars, and creatinine all form interference with copper ions to cause interference. These interferences can be avoided by changing the copper of the biuret reagent to nickel (Clinical Chemistry (19) (1990), 300-306), but the reaction is slower when nickel is used, so it can be measured with an automatic analyzer. Without
In addition, there is a problem that the measurement wavelength overlaps with bilirubin, so that the measurement wavelength is affected by bilirubin interference.

[0009] In the method of Doumas et al., Since sodium potassium tartrate is used as a chelating agent, dextran contained in an infusion causes an insoluble precipitate, which makes measurement impossible. Therefore, recently, EDTA or the like has been used as a chelating agent. However, when such a chelating agent having a large chelating power is used, there is a disadvantage that in the determination of the total protein, the color is not sufficiently formed unless the alkalinity is increased. High-concentration alkaline substances are not only dangerous to handle, but also harmful as environmental pollutants, and have problems such as difficulty in treating waste liquid.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and a reagent for quantifying total protein which can avoid the influence of an interfering substance which has been a problem in quantifying total protein.

[0011]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have obtained a method and a reagent for quantifying total protein which can avoid the influence of an interfering substance. Successful.

The present invention is as follows. (1) A method for quantifying total protein in a sample, which comprises reacting the sample with a reagent containing copper ions and then reacting it with a reagent containing an alkaline solution. (2) The method according to (1) above, wherein the pH of the reagent containing copper ions is in the range of 10 to 13. (3) The method for quantifying total protein according to the above (1) or (2), wherein the alkaline solution is a lithium hydroxide solution. (4) A reagent for quantifying total protein comprising a first reagent containing copper ions and a second reagent containing lithium hydroxide. (5) The reagent according to (4) above, wherein the pH of the first reagent containing copper ions is in the range of 10 to 13.

In the present invention, a sample is mixed with copper ions under the condition that the protein does not develop color, and then mixed with an alkaline solution to form a complex of the protein and copper ions to develop color. The difference in absorbance is measured at a main wavelength of 546 nm and a sub wavelength of 700 nm, and the total amount of protein in the sample is quantified by comparing with the absorbance of the standard solution.

In the method for quantifying total protein of the present invention,
First, the reagent is reacted with a reagent containing copper ions and then with a reagent containing an alkaline solution. As a reagent containing a copper ion, any reagent that meets the purpose of the present invention can be used. For example, a copper sulfate solution, a copper chloride solution, a copper nitrate solution and the like are exemplified. The final concentration of copper ions in the reaction solution is usually 3 to 3 when copper sulfate is used, for example.
It is about 30 mM, preferably about 6 to 20 mM. The solution preferably has a pH of 10-13. By setting the pH to 10 or more as shown in Examples 1 and 2 (FIGS. 1 and 2), it is possible to avoid interference of a dye that develops on the alkaline side such as hemoglobin dye, hemoglobin protein and BSP. However, when the pH is higher than 13, the protein develops color and interferes with the measurement. The reagent containing copper ions can be included as the first reagent in the total protein determination reagent. The first reagent may optionally contain a chelating agent, if desired. Examples of chelating agents that can be used include EDTA, sodium potassium tartrate, glycol ether, diaminetetraacetic acid and the like. The final concentration of the chelating agent in the reaction solution is usually 1 to 10 times, preferably 1.2 to 3 times the copper ion. EDTA is preferably used to avoid the formation of insoluble precipitates due to dextran from infusions that may be present in the sample.

In the present invention, any alkali solution to be added later can be used as long as it meets the purpose of the present invention. Specific examples include sodium hydroxide, lithium hydroxide, and potassium hydroxide, and more preferably, lithium hydroxide is used. The higher the alkali concentration, the higher the color development sensitivity. However, in the present invention, since the two-reagent method is used, if the alkalinity of the alkali solution of the second reagent is high, the viscosity increases and the error in dispensing increases. And the reproducibility is reduced. However, the same sensitivity can be obtained at a concentration of about 1/3 that of lithium hydroxide, for example, as compared with sodium hydroxide, and the viscosity of the second reagent can be kept low. it can.
A reagent containing an alkaline solution can be included as a second reagent in the total protein determination reagent. The final concentration of the alkali in the reaction solution is 0.2 to 2 M when sodium hydroxide is used, preferably about 0.3 to 1 M, and 0.2 to 0.5 M when lithium hydroxide is used.
Preferably it is about 0.35 to 0.45M.

In order not to be affected by the dispensing accuracy of the automatic analyzer and to reduce the reproducibility, the amount of the reagent containing copper ions, which is the first reagent added first in the present invention, is the second reagent added later. It is preferable that the amount is larger than the amount of the reagent containing the alkaline solution as the reagent.

[0017]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

Example 1 The first reagent was 15 mM copper sulfate, 30 mM EDTA, 0.1 mM
Add 1M glycine and adjust the pH to 7-1 with sodium hydroxide.
The one adjusted to 3 was used. The second reagent is 2
It was prepared to be M lithium hydroxide. 1/10 volume of 5 g / dl hemoglobin was added to human serum having a known protein concentration (7.7 g / dl). The prepared hemoglobin-added sample (human serum protein: 7.7 g / dl × 0.9 =
6.93 g / dl, hemoglobin protein: 5 g / dl ×
0.1 = 0.5 g / dl), 8 g / dl protein standard solution and 10 µl each of physiological saline were added with 400 µl of the first reagent, reacted at 37 ° C for 5 minutes, and a reagent blank (saline) was used as a control. The respective absorbance differences at a wavelength of 546 nm and an auxiliary wavelength of 700 nm are measured. Next, the second reagent 100μ
After addition of 1 and reaction at 37 ° C. for 5 minutes, the absorbance difference is measured again. The difference in absorbance before and after is volume-corrected to determine the difference absorbance. The protein concentration of the hemoglobin-added sample is determined by comparing the absorbance difference between the hemoglobin-added sample and the protein standard solution. The total protein concentration of the hemoglobin-added sample at each pH was plotted (FIG. 1).

By setting the pH of the first reagent to around 11, the influence of not only the hemoglobin dye but also the hemoglobin protein is eliminated. It is a problem as a measurement method that the measurement is not affected by the hemoglobin protein, but it is better not to be affected by the hemoglobin protein when used for clinical diagnosis. In the present invention, interference of (hemoglobin dye + hemoglobin protein) due to hemolysis can be avoided by adjusting the pH of the first reagent.

Example 2 The same operation as in Example 1 was performed except that a 10 mM BSP solution was used instead of 5 g / dl hemoglobin. Compare the difference in the absorbance of the BSP-added sample with the difference in the absorbance of the protein standard solution.
The total protein concentration of the P-added sample is determined. B at each pH
The protein concentration of the SP-added sample was plotted (FIG. 2).

By setting the pH of the first reagent to 10 or more, interference from BSP is eliminated. However, if the pH is 13 or more, the protein develops color, so it is desirable to use the pH in the range of 10 to 13.

Example 3 The first reagent was 15 mM copper sulfate, 30 mM EDTA, 0.1 mM
Add 1M glycine and 0.8M sodium carbonate to pH1
Those prepared with sodium hydroxide in 1.3 were used.
The second reagent was prepared to be 2M lithium hydroxide.
1/10 volume of physiological saline, chyle, hemoglobin, bilirubin, BSP and glycine, glycylglycine, creatinine, urea, ammonium sulfate, glucose and galactose which are said to be positive for biuret reaction are added to 2 g / dl human serum albumin did. Each substance was added to each of the addition concentrations (concentrations in the sample) shown in Table 1. Each sample was operated in the same manner as in Example 1. Using a sample added with physiological saline as a standard solution having a protein concentration of 1.80 g / dl, the total protein concentration of each sample was determined.

Comparative Example 1 (Quantification by the method of Doumas et al.) 12 mM copper sulfate, 32 mM sodium potassium tartrate,
A solution containing 30 mM potassium iodide and 0.6 M sodium hydroxide is prepared as Doumas reagent. 500 μl of Doumas reagent was added to 10 μl of each sample prepared in Example 3 and reacted at 37 ° C. for 10 minutes, and the absorbance at a wavelength of 546 nm was measured using a reagent blank as a control. Also,
A reagent was prepared by removing copper from the above Doumas reagent, and the same operation was performed to measure a sample blind. The value obtained by subtracting the sample blind from the measured value using the Doumas reagent was measured. Total protein concentration of each sample according to the present invention of Example 3 and Do of Comparative Example 1
Table 1 shows the total protein concentration of each sample with the umas reagent and the total protein concentration of each sample after the sample blank was subtracted from the total protein concentration.

[0024]

[Table 1]

The method of subtracting the sample blind using the Doumas reagent clearly showed an improvement in the way of receiving interference as compared with the method of not subtracting. However, there is no effect on bilirubin interference. Bilirubin in the sample is changed to biliverdin due to copper ions, but in the method of subtracting the sample blind using Doumas reagent, bilirubin remains as bilirubin because the reagent does not contain copper ions, so correction cannot be made even if the sample blind is subtracted Because. Reaction with two reagent system,
DuPont's total protein TP to be measured does not require sample blinding and avoids interference from chyle or hemolysis. However, even with this method, interference by bilirubin cannot be avoided. This is because, in the case of DuPont's total protein TP, bilirubin remains in the bilirubin state before coloring due to the addition of an alkaline solution and copper ions later, but changes to bilirubin after coloring, so the difference in absorbance between bilirubin and bilirubin This is because interference occurs. In the present invention, the use of two reagents and the addition of copper ions first eliminates interference with chyle, hemoglobin, bilirubin, BSP and biuret-positive substances. In the present invention, bilirubin-biliverdin does not interfere with the absorbance difference before and after color development because the measurement is performed after conversion into biliverdin before and after color development.

[0026]

The method of the present invention for quantifying total protein is a two-point measurement using a two-reagent system, which eliminates the need for sample blinding and avoids interference with chyle and hemolysis. By adding copper ions to the reagent to be added first, it is possible to avoid the effects of bilirubin interference and the effects of biuret reaction-positive substances such as amino acids, saccharides, and creatinine. Further, by adjusting the pH of the reagent to be added first to 10 to 13, there is no influence of substances that develop color on the alkaline side such as hemoglobin protein and BSP. In addition, by preparing an alkali solution to be added later with lithium hydroxide, measurement can be performed with high sensitivity with a small amount of alkali, so that the viscosity can be suppressed to a low level and a decrease in reproducibility due to an error in dispensing can be suppressed. Further, since only a small amount of the alkaline solution is used, the treatment of waste liquid is easy and a safe reagent can be supplied. By using the reagent containing copper ions to be added first as the first reagent and the alkali solution to be added later as the second reagent, the reagent for quantifying the total protein of the present invention can be prepared.

[Brief description of the drawings]

FIG. 1 is a graph showing the influence of pH on hemolysis interference.

FIG. 2 is a graph showing the effect of pH on BSP interference.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-64-18059 (JP, A) JP-A-62-203063 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 33/68 G01N 31/00 G01N 31/22 122

Claims (6)

(57) [Claims] 1. A specimen formed by reacting a specimen with a reagent containing copper ions and then reacting with a reagent containing an alkaline solution.
The method of quantifying the total protein in a sample characterized that you measure the color of the complex of protein and copper ions in. 2. After reacting a sample with a reagent containing copper ions.
The absorbance is measured at a later time, and then
And then measure the absorbance again.
A method for quantifying total protein in the body. 3. A method of quantifying according to claim 1 or 2 Total protein according pH of the reagent containing copper ions is in the range of 10-13. 4. A method of quantifying the total protein according to any one of claims 1 to 3 alkaline solution is lithium hydroxide solution. 5. A reagent for the determination of total protein of a second reagent containing a first reagent and lithium hydroxide containing no copper ions only contains and azo dyes. 6. The pH of the first reagent containing copper ions is 10-1.
The reagent for quantifying total protein according to claim 5, which is in the range of 3.