Serum calcium

Calcium is the most abundant cation in the human body. The atomic formula is Ca, and the atomic weight is 40.08. Normal adults contain 25-30 mol of calcium, more than 99% of which are found in bones and teeth. The bone is the largest reservoir of calcium in the body. The extracellular fluid contains only about 27 mmol of calcium. Although it is low in content, it maintains normal neuromuscular stress. Glandular secretion and the activity of some enzyme systems play an important role especially in the process of blood coagulation. The intracellular fluid contains almost no calcium. Basic Information Specialist classification: growth and development check classification: biochemical examination Applicable gender: whether men and women apply fasting: fasting Tips: Specimens should be measured as soon as possible, preferably within 1 hour after sampling. Normal value (1) Methyl thymol blue colorimetric method (MTB) 1 serum calcium adult 2.03 ~ 2.54mmol / L. Children 2.25 ~ 2.67mmol / L. 2 serum ionized calcium 1.13 ~ 1.35mmol / L. 3 Red blood cells Calcium in whole blood is almost in the plasma, and only 15.72 μmol / L of packed cells in red blood cells. 4 urinary calcium excretion varies greatly with diet. A. <3.75mmol/24h for low calcium diet. B. <6.25mmol/24h for general calcium diet. C. High calcium diet can reach <10mmol/24h. 5 salivary calcium 0.74 ~ 1.69mmol / L. (2) o-cresol oxime complex ketone direct colorimetric method (MTB) method. (3) Ethylenediaminetetraacetic acid disodium titration method (MTB) method. (4) Determination of serum ionized calcium by ionized calcium: 1.10 to 1.34 mmol/L for adults. Clinical significance (1) Ethylenediaminetetraacetic acid disodium titration 1 increased blood calcium A. There are two primary and secondary hyperthyroidisms. Secondary to rickets, rickets and chronic renal failure. The increase of blood calcium is more than 2.6mmol/L, the highest is up to 4.5mmol/L, and the blood phosphorus is reduced, less than 1.13mmol/L, and the lowest is 0.64mmol/L. Urinary calcium increased, male was greater than 9.68mmol / 24h, female was greater than 8.07mmol / 24h. B. Vitamin D hyperactivity can increase serum calcium and phosphorus, and calcium deposition in the kidney can develop into renal calcification. C. Multiple myeloma increased blood calcium often due to increased globulin and increased calcium binding. D. Tumor extensive bone metastasis Blood calcium is moderately increased, but phosphorus is normal or slightly higher, urinary calcium excretion increases, urinary hydroxyproline excretion increases, reflecting the decomposition of bone collagen. E. Addison's disease. F. Sarcoidosis due to excessive absorption of calcium in the intestine, which increases blood calcium and blood phosphorus is slightly higher. 2 blood calcium lowering blood calcium can cause neuromuscular stress and increase the hand and foot spasm, can be seen in the following diseases: A. Hypoparathyroidism decreased during thyroidectomy and parathyroidism caused by dysfunction, serum calcium can be reduced to 1.25 ~ 1.50mmol / L, serum phosphorus can be increased to 1.62 ~ 2.42mmol / L, pseudo-parathyroid function Decreased is not a lack of parathyroid hormone, and the kidney lacks adenylate cyclase that responds to parathyroid hormone, causing a decrease in serum calcium. B. Chronic nephritis uremia The deficiency of vitamin D3-1 hydroxylase in the renal tubules, the deficiency of active vitamin D3, the serum total calcium decreased, due to the reduction of plasma albumin, the combined calcium is reduced, but the metabolic acidosis increases the ionized calcium. , so it is not easy to happen. C. Lack of vitamin D in rickets and rickets, calcium absorption disorders, serum calcium and phosphorus are low. D. Absorptive Hypocalcemia In the case of severe celiac disease, calcium in the diet and calcium non-absorbed fatty acids are excreted. E. A large amount of input of citrate anticoagulant can cause hypocalcemia of the hand and foot. (2) Determination of ionized calcium: 1 Determination of ionized calcium is most important for larger surgical procedures, such as cardiac surgery, transplantation and other anticoagulation operations requiring large amounts of citrate or postoperative sepsis, renal, cardiopulmonary failure, Or burn patients, because the level of serum protein has been reduced in these states, acid-base imbalance and the input of citrate blood products, repeated determination of total calcium has no meaning. If calcium is to be supplemented, ion calcium determination is the best guide for proper treatment of these patients. 2 When neonatal hypocalcemia is suspected, ionized calcium should be measured. If complications continue to occur, it should be measured frequently. 3 Kidney Diseases After kidney transplantation, or in patients undergoing hemodialysis, calcium metabolism often changes and is sometimes intense. Therefore, maintaining a slight blood calcium balance during hemodialysis is important to maintain good cardiac function. The determination of ionized calcium is the best means of monitoring. Nephrotic syndrome is characterized by a decrease in serum protein, and total calcium and ionized calcium levels are reduced. Correcting total calcium at protein levels may cause overestimation of ionized calcium. 4 In patients with primary hyperparathyroidism, ion calcium increased in more than 90% of cases, and total calcium increased in about 80% of cases. 5 In patients with acute pancreatitis, ionized calcium decreased within 24 hours after onset, and returned to normal at 48 hours. Total calcium was also slightly reduced at 48 h, when sustained albumin reduction was associated with severe pancreatitis due to decreased albumin. 6 The percentage of elevated ionized calcium in patients with malignant tumors is greater than total calcium, and may be used in screening tests for tumors. When the cause of hypercalcemia is difficult to determine, the presence of malignant tumors must be considered. Precautions (1) Methyl thymol blue colorimetric method (MTB): 1MTB has a similar aminocarboxyl structure with EDTA, 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. The dosage of 3EDTA is selected. The complexation 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 tubes used were washed and soaked twice with deionized water, then baked and ready for 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 oxime complex ketone direct colorimetry: 1 This test uses serum or heparin anticoagulated plasma samples. Specimens that cannot use calcium chelating agents (EDTA-Na2) and oxalate as anticoagulants. 2 o-cresol 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 reagent added 8-hydroxyquinoline to eliminate the interference of magnesium, can specifically complex magnesium, 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 alkaline buffer for determination of serum calcium, can be selected according to the conditions, commonly used ethylene diamine-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 color developer 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 test specimen has jaundice or hemolysis, the end point is not easy to observe, then the specimen must be treated. First, calcium is precipitated with oxalate, and then re-dissolved with hydrochloric acid and sodium citrate. A. Several reagents need to be added: 0.7 mol/L ammonium oxalate; 0.05 mol/L sodium citrate; 1 mol/L hydrochloric acid. B. Press the following method: Pipette 0.1 ml of serum, place it in a centrifuge tube, add 0.25 ml of deionized water, 0.05 mol of ammonium oxalate 0.05 ml, 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 The calcium indicator has a wide variety of names, and the name is disordered. The different titration ends of different indicators are different, and the effects of interference by other ions are different. The end point of the 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 Determination of ionized calcium is best to use serum. 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 pH changes have a greater impact 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 determined as soon as possible, preferably within 1 hour 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 Ionized calcium content is also related to the following factors: A. Standing can increase the ionized calcium by about 1% to 2%. B. 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. C. Staying in bed for 3 to 12 days is sufficient 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 performs display and electronic circuit detection, and the two-point slope calibration can be performed after the end. 2 When the slope is calibrated, 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 sent after the “beep” sound is removed. 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 measurement can be performed. A. Capillary blood measurement: Mix the capillary blood, push out the suction needle, remove the plug at both ends, attach the connector at one end, and install the other end of the connector on the sampling needle. Press the “Measure” button until the sample is completely filled with the sample. After the cavity, release the “Measure” button and the sample 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. B. The serum measurement process is measured with whole blood. 4 After 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 No taboos. Adverse reactions and risks Subcutaneous hemorrhage: subcutaneous hemorrhage due to less than 5 minutes of compression time or blood draw technique.