Blood chemistry

Blood chemistry

These tests cover total cholesterol, total protein , and various electrolytes in the body , such as sodium , potassium , chlorine, and many others. The rest of the tests examine the chemicals that help the liver and kidney break down various substances.

  • Preparation for the exam

The patient should try not to eat anything the night before the exam .



  • Normal values*

It is 52.8-66.6% of the total proteins, that is, the main whey protein and its normal values ​​in g / 100 ml are comprised between:

  • 9 and 5.5 in newborns.
  • 8 and 5.5 in children.
  • 3 and 6.1 in men.
  • 7 and 5.6 in women.

It is important to maintain the blood oncotic pressure, and for the transport of ions, hormones, amino acids, drugs, etc. It is synthesized in the liver and, therefore, serves as an indicator of liver function. Apart from the accuracy of the electrophoretic-densitometric analysis, albumin can be determined by fixing the bromocresol purple and then measuring the displacement of its absorption maximum at 603 nm. Other common methods are the calculation of the tryptophan content in albumin with respect to globulins, and immunochemical techniques such as turbidimetry, nephelometry, electroimmunoassay and radial immunodiffusion.

There is a glycoprotein called prealbumin (18-45 mg / dl). Its quantification is currently performed by kinetic nephelometry. Its decrease is notable in severe liver disease, burns and malnutrition.

Alkaline phosphate

The activity of total alkaline phosphatase (ALP), normally determined in serum, comes mainly from the bones and the liver, although it is also present in other tissues. Normal values ​​are between 85-190 U / L, being triple in pregnancy, at the end of the first trimester. In children of growing age, serum levels are higher due to the increase in the bone fraction due to osteoblastic activity. Figures vary greatly with age and sex:

  • 250 U / l in newborns.
  • 350 U / l in children from 1 to 12 years old.
  • 280 U / l in girls from 10 to 14 years old and 275 U / l in boys of the same age,

and 500 U / l in males between 12 and 15 years old.

  • 150 and 155 U / l in girls and boys aged 15 to 19, respectively.
  • 85-110 in adult women and 90-135 in adult men.

ALP values ​​increase in obstructive jaundice, bile duct neoplasms, biliary cirrhosis, diabetes with liver degeneration, liver diseases such as cirrhosis, hepatomas, sarcoidosis, periarteritis nodosa, cholelithiasis, etc. It also increases in primary hyperparathyroidism. , Paget’s and Recklinghausen’s diseases, osteogenic neoplasms of the bone, prostate cancer with bone metastases, severe rickets, osteomalacia, congenital hyperphosphatasia and in intrahepatic cholestasis due to chlorpromazine. No elevation is seen in osteolytic bone tumors, myeloma, or osteoporosis.

  • 145-165 U / l in women 65 years of age and older and 140-190 U / l in men of

The same age.


Values ​​range from 15 to 50 mg / dl. It is usually expressed as BUN or blood urea nitrogen by volume (urea = BUN x 2,146). It is indirectly quantified by conversion to ammonia using urease. (See the analysis methods in the following section 5.2.-Ammonia) Its increase may be due to prerenal, renal and postrenal causes. Among the former, we must mention the pictures of shock, dehydration, congestive heart failure, hepatorenal syndrome, sepsis, hemorrhages, acidosis, extensive burns and all those processes that cause a picture of protein catabolism. Renal diseases include pathologies with acute or chronic kidney failure, and obstructive uropathy as an example of postrenal disorders. Urea decreases in excessive fluid intake, pregnancy, and severe liver disease.

Calcium in Serum

Metabolically active calcium is ionized. Its determination requires the use of a complex technique, so what is usually measured is total calcium. This is made up of free calcium (46%), bound to albumin (32%), globulins (8%) and forming diffusible complexes (14%). It is determined in serum or heparinized plasma rapidly separated from the cells. EDTA and oxalate should not be used as anticoagulants because they are calcium chelators.

Serum Chloride

Normal values ​​range from 101-111 mmol / l. Chlorine values ​​are highly influenced by variations in other ions, mainly sodium, which is usually followed by changes, and bicarbonate, with changes in the opposite direction. The method of analysis of choice is coulometric titration; Insoluble silver chloride is formed from ionic silver.

Hypochloremia occurs from repetitive vomiting, gastric or tube lavage, severe diarrhea, intestinal ileus, excessive sweating, fistulas, metabolic acidosis, adrenal insufficiency, hyperparathyroidism, myxedema, kidney failure, renal tubulopathies, burns, diuretic and bromide poisoning, pancreatitis, liver failure and cirrhosis, and respiratory acidosis accompanied by hypercapnia.

Hyperchloremia with hypernatremia is observed in cases of hemoconcentration as in dehydration and in the administration of saline parenteral solutions, as well as in diabetic ketosis, renal failure and nephrogenic diabetes insipidus.


Its serum concentration is proportional to the muscle mass of the body. Normal figures range from 0.5 to 1.3 mg / dl for men and from 0.4 to 1.1 mg / dl for women. The Jaffé method described in 1886 is still the one in force and consists of the formation of a red complex that absorbs at 510 nm, from the reaction at alkaline pH between creatinine with picric acid. There is a correlation between serum creatinine and creatinine clearance to calculate the degree of glomerular failure. It is used to evaluate renal dysfunctions both in diagnosis and treatment, it is the case of monitoring dialysis patients. Its increase indicates kidney failure, circulatory failure and urinary obstructions.


The average figure is 0.5 mg / dl, but the values ​​can vary from 0.2 to 1.2 mg / dl. In newborns the values ​​are higher (1-12 mg / dl). Two types are distinguished, according to the reaction of van den Bergh. The water-soluble bilirubin, which reacts directly and rapidly with the diazoreactive, is bilirubin conjugated with glucuronic acid. Unconjugated or indirect bilirubin that is bound to albumin, is insoluble in water and reacts late or in the presence of alcohol. The latter is the one that predominates in the serum under normal conditions (0.05-0.4 mg / dl).

The procedure that is carried out for the determination of bilirubin in cases of uremic patients, especially on hemodialysis or with kidney transplantation and in newborns to analyze the direct fraction, is the Jendrassik endpoint kinetic method, based on the Diazotization of bilirubin at neutral pH to form a colored chromophore and the absorbance of azobilirubin is measured at 600 nm after subjecting the reaction solution to pH 13. To determine the unconjugated fraction, azolylirubin is measured at pH 1, 2 to 560 nm.

Serum Sodium

Serum levels are normally 135 to 145 mmol / l. The reference method is atomic or flame emission spectroscopy, but the currently automated potentiometry with selective ion electrode (ISE) and with glass ion exchange membrane can be used. Finally, atomic absorption.

Hyponatremia appears due to excessive sweating, vomiting, fistulas, diarrhea, Addison’s disease and hypoaldosteronism, acidosis, cardiac decompensation, nephrosclerosis, diabetes mellitus, cirrhosis, due to excessive administration of diuretics, salt-free diets, adrenogenital syndrome of the newborn, hypertensive syndrome, retention tissue in infections such as pneumonia, diabetic hyperglycemia, etc.

Hypernatremia occurs in situations of simple dehydration, excess administration of saline, Conn syndrome, Cushing’s disease, hyperosmolar diabetic coma, etc.


The normal figure is between 140 and 200 mg / dl, although it varies according to the techniques and reference values ​​established in the laboratories. It is also influenced by diet, age, and sex. In pregnancy (from the 5th month) and after delivery, their values ​​rise. Free (25%) and esterified (75%) cholesterol are distinguished.

The Liebermann-Burchard non-enzymatic colorimetric reaction stands out from all the analysis methods for total cholesterol. Currently the enzymatic endpoint colorimetric test is automated and very easy and accurate. As a definitive technique, mass spectrometry with isotopic dilution is recommended. Increased cholesterol occurs in cases of obstructive jaundice, cholelithiasis, biliary cirrhosis, myxedema, nephrotic syndrome, diabetes, xanthomatosis, familial idiopathic hyperlipemia, essential hypercholesterolemia, chronic alcoholism, idiopathic hypercalcemia in children, kidney transplants, hypothyroidism, etc. Hypercholesterolemia is related to atherosclerosis, although it may be absent in some cases.

Hypocholesterolemia is normal in children and the elderly and pathological in cases of liver failure, hyperthyroidism, anemia (pernicious, hemolytic and hypochromic), acute infections (eg pneumonia), states of starvation and malabsorption, pulmonary tuberculosis, terminal nephritis, uremia, disease of Addison, myeloproliferative syndromes, Tangier disease (absence of alpha-lipoproteins) and congenital abetalipoproteinemia.

Furthermore, cholesterol can be linked to several lipoproteins: – HDL-Cholesterol. It is the one that is linked to high-density lipoproteins and protects from atherogenesis. Its normal values ​​are between 33 and 55 mg / dl in men and between 45 and 65 mg / dl in women. Precipitation techniques are those that are frequently used and are based on separating the largest and least dense lipoproteins (LDL), by means of polyanions in the presence of divalent cations (heparin-manganese chloride or dextran sulfate-magnesium chloride), thus HDL remains in the supernatant and is quantified by a gravimetric enzymatic determination of the particles.

– LDL cholesterol. It is that of low-density lipoproteins, produces atherogenesis and its normal values ​​are 150-190 mg / dl. – Cholesterol-VLDL: It is the one that is linked to very low density lipoproteins. It is also atherogenic and its figures range between 20 and 26 mg / dl. It can be calculated from the triglyceride / 5 ratio, provided that the triglyceride level is less than 400 mg / dl. Likewise, LDL-cholesterol is total cholesterol minus the sum of VLDL-cholesterol and HDL-cholesterol.


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