Serum calcium (Ca2+, Ca)

Calcium ion concentration in serum. More than 99% of the body's calcium is found in bones and teeth. Most of the calcium in the blood is present in the plasma, and plasma calcium has two parts: non-diffusive calcium and diffuse calcium. Non-diffusive calcium binds to protein (about 1g protein binds 0.87mg of calcium), about 40% to 50% of total plasma calcium, diffuse calcium is mainly ionized calcium (Ca2+), and a small part of calcium salt (such as Calcium citrate, other organic acid calcium salts and calcium bicarbonate, etc.). The non-diffusive calcium and diffuse calcium are affected by the H+ concentration and the HCO3-concentration, and are balanced under physiological conditions.

Basic Information

Specialist classification: growth and development check classification: biochemical examination

Applicable gender: whether men and women apply fasting: fasting

Analysis results:

Below normal:
Reduced in infants with hand and foot sputum, hypoparathyroidism, osteomalacia, calcium or vitamin D malabsorption or deficiency (rickets, diarrhea, late pregnancy, etc.), obstructive jaundice, acute hemorrhagic pancreatitis, kidney disease (such as Chronic nephritis, uremia, alkalosis, and dehydration and acidosis (usually hypocalcemia). In addition, causing serum albumin to reduce diseases such as malignant tumors, severe liver diseases, kala-azar, etc. can also reduce blood calcium.

Normal value:
Adult: 2.1-2.75mmol/L
Children: 2.25-3.0mmol/L

Above normal:
Increased in hyperparathyroidism, parathyroid tumors, excessive intake of vitamin D, multiple myeloma, tumor bone metastasis, acute bone atrophy.



Tips: Before the examination, the diet is light and alcohol is prohibited. Check for an empty stomach in the morning. Normal value

Adults 2.1 to 2.75 mmol/L (8.5 to 11.0 mg/dl).

Children 2.25 ~ 3.0 mmol / liter (9.0 ~ 12.0 mg / dl).

Clinical significance

1, increased in hyperparathyroidism, parathyroid tumors, excessive intake of vitamin D, multiple myeloma, tumor bone metastasis, acute bone atrophy.

2, reduced in infants with hand and foot sputum, hypoparathyroidism, osteomalacia, calcium and vitamin D malabsorption or deficiency (rickets, diarrhea, late pregnancy, etc.), obstructive jaundice, acute hemorrhagic pancreatitis, kidney disease (such as chronic nephritis, uremia), alkalosis and after dehydration and acidosis correction (often hypocalcemia). In addition, causing serum albumin to reduce diseases such as malignant tumors, severe liver diseases, kala-azar, etc. can also reduce blood calcium.

Low results may be diseases: neonatal hypocalcemia, muscle spasm, giant disease and acromegaly

1. Methyl thymol blue colorimetric method (MTB):

(1) MTB and EDTA have similar aminocarboxyl structures, which can chelate a variety of cations, but the complexation constants are different.

(2) Addition: The role of EDTA is to mask contaminated calcium and other metal ions in the reagent. It can reduce the absorbance of the blank tube and increase the absorbance of the measuring tube, thereby improving the sensitivity of the method.

(3) The dosage of EDTA is selected. The complex stability constant of most metal ions and EDTA is greater than that of calcium, and only a few trace elements are less than calcium. A limited amount of EDTA can only mask the interfering elements in the reagent, and there is no excess EDTA complexing serum calcium. Generally, the concentration of EDTA is 99-108 μmol/L in the reagent, and the final EDTA concentration of the color reaction is 50-54 μmol/L.

(4) The test tube used is washed twice with deionized water and then baked for later use. After the cleaning tube is added to the reagent, it should be consistently light gray-green. If it is blue, the tube indicates calcium contamination.

2, o-cresol 酞 complex ketone direct colorimetry:

(1) Serum or heparin anticoagulated plasma samples for the assay. Specimens that cannot use calcium chelating agents (EDTA-Na2) and oxalate as anticoagulants.

(2) o-cresolphthalein is an acid-base indicator similar in structure to methyl thymol blue, colorless in a neutral or acidic environment, and complexed with calcium ions in an alkaline solution to be purplish red. Therefore, pH has a great influence on the color development. At pH 10.5 to 12, the reaction sensitivity is the best, so pH 11 is preferred.

(3) Adding 8-hydroxyquinoline to the reagent to eliminate the interference of magnesium, can specifically complex magnesium, and TritonX-100 has the effect of digesting protein. Some authors also added cyanide to mask other metal ions in the reagent; dimethyl sulfoxide eliminates the influence of protein and inhibits the dissociation of o-cresol ruthenium complex, thereby reducing the absorbance of the blank; polyvinylpyrrolidone can also eliminate protein, Interference with bilirubin and phosphorus.

(4) There are many alkaline buffers for determination of serum calcium, which can be selected according to the conditions. Commonly used are ethylenediamine-potassium cyanide, ethylenediamine-potassium acetate-hydrochloric acid, ethylenediamine-ethylene glycol, Ethanolamine-boric acid, 2-amino-2-methyl-1-propanol, and the like. The coloration was determined by using ethylenediamine-ethylene glycol buffer. The ethanolamine-boric acid buffer has a large buffer capacity and allows the absorbance of the blank reagent to be kept low. 2-Amino-2-methyl-1-propanol is non-toxic, non-irritating and also allows for a lower reading of the blank tube.

(5) The coloring agent sometimes crystallizes slightly, and the 8-hydroxyquinoline has a low solubility in water and is easily precipitated by crystallization. In this case, the supernatant solution can be used.

3. Ethylenediaminetetraacetic acid disodium titration method

(1) If the specimen has jaundice or hemolysis, the endpoint is difficult to observe, the specimen must be treated. First, calcium is precipitated with oxalate, and then reconstituted with hydrochloric acid and sodium citrate.

1 Several reagents need to be added: 0.7 mol/L ammonium oxalate; 0.05 mol/L sodium citrate; 1 mol/L hydrochloric acid.

2 Press the following method: Pipette 0.1ml of serum, place it in a centrifuge tube, add 0.25ml of deionized water, 0.05ml/L ammonium oxalate 0.05ml, and mix. Place in a 56 ° C water bath for 15 min. Centrifugation was performed at 2000 rpm for 10 min. Carefully pour the supernatant and place the tube on the filter paper and blot dry. 0.1 ml of each of 1 mol/L hydrochloric acid and 0.05 mol/L sodium citrate was added to a centrifuge tube to dissolve the precipitate. Titration and calculation by direct titration.

(2) There are many kinds of calcium indicators, and the names are chaotic. The different titration ends of different indicators are different, and the effects of interference by other ions are different. The end point of calcium red indicator is obvious, and it is less affected by magnesium ions. But it is not stable. Always freshly configured, immediately add to the specimen and titrate with EDTA-Na2. The calcium red used is calcium-carboxylate, which should be distinguished from the alias "calcium red" of glyoxal bis-aminophenol.

4. Determination of ionized calcium:

(1) It is preferable to use serum for the determination of ionized calcium. Advantages do not participate in anticoagulants, reducing protein contamination of the electrodes. Heparin anticoagulated whole blood can also be used for the determination of ionized calcium, especially in the urgent need to reduce the clotting time and the time to centrifuge the serum. However, an excess of heparin (30 u/ml) can reduce the ionized calcium concentration by 3% to 5%.

(2) The pH change has a great influence on Ca2+. The decrease in pH can increase Ca2+, and vice versa, so that the calcium ions are reduced, so the blood samples collected can prevent CO2 from escaping as much as possible and avoid pH increase.

(3) Specimens should be measured as soon as possible, preferably within 1 h after sampling. Whole blood sealed in a refrigerator at 4 ° C for 6 h or longer. The serum sealed in the syringe can be stored at room temperature for 1 to 2 hours if there is no air bubble, and can be stored for more than 24 hours at 4 °C.

(4) The ionized calcium content is also related to the following factors:

1 standing can increase the ionized calcium by about 1% to 2%.

2 prolonged venous congestion can increase the ionized calcium by 2%, and the ionized calcium can increase by 8% in the forearm movement for a few minutes.

3 bed for 3 to 12 days is enough to make the ionized calcium out of the normal range.

Inspection process

Determination of ionized calcium: The calcium electrode used in the commercial ionized calcium analyzer uses a neutral carrier as the active material of the calcium electrode to form a polyvinyl chloride (PVC) electrode film. The life of the electrode is about half a year: the pH electrode is made of special glass capillary The reference electrode is made of silver/silver chloride.

The reagent formula, reagent dosage, and operation method of various types of ionized calcium analyzers are different. Generally, the following steps are required. This method takes a domestic ionized calcium analyzer as an example.

1. Connect the power supply. The instrument first displays and electronically detects the signal. After the end, the two-point slope calibration can be performed.

2. When the slope is set, the suction needle is immersed in the vial containing the low and high two-concentration slope calibration instrument, and the slope calibration solution is taken up, and the instrument is removed after the “beep” sound is emitted. The sample is pushed back to the original position and the instrument automatically performs the slope calibration.

3. After the calibration is passed, the sample can be measured.

(1) Capillary blood measurement: Mix the capillary blood, push out the suction needle, remove the plug at both ends, attach the connector at one end, mount the other end of the connector on the sampling needle, and press the “Measure” button until the sample is completely filled with the sample. After measuring the chamber, release the “Measure” button and the injection pump stops working. At this time, the sample in the sample measuring chamber should be inspected for bubbles. If there are air bubbles, please release the “Measure” button for 8 seconds, then press the “Measure” button to continue to suck the sample until the bubbles are eliminated. Remove the sample, wipe the sample and push it back in place, and display the measurement data and print the result after 8 s of the injection.

(2) The serum measurement process is measured with whole blood.

4. When the specimen is measured, the instrument is flushed with the pipeline and the sample is measured. After the rinse is completed, the next sample can be measured.

5. The instrument will enter the “sleep” state after 10 minutes of the last calibration or blood sample measurement. At this time, if blood sample measurement is required, a certain calibration must be performed first. If there is no blood sample measurement, the instrument automatically performs a one-point calibration every 30 minutes.

Not suitable for the crowd

Those who do not have an indication for examination should not be examined.

Adverse reactions and risks

Risk of infection: If you use an unclean needle, you may be at risk of infection.