Lab No.1 October 2015
Role of clinical biochemistry laboratory
To perform mainly quantitative and some qualitative analyses on body fluids such as blood, serum, plasma, urine and cerebrospinal fluid as well as feces, calculi and sometimes tissues and other materials.
Biochemical tests are important in the diagnosis, management, and follow up of a lot of diseases:
Diagnosis of diabetes mellitus depends on the finding of elevated serum glucose level.
The finding of the high serum cholesterol level is associated with a risk of atherosclerosis.
Estimation of serum bilirubin confirms a diagnosis of jaundice and whether it is hepatic or hemolytic.
Diagnosis of acute pancreatitis depends mainly on estimation of serum or urine amylase enzyme level.
Estimation of organ –specific enzymes can detect damage in that organ.
Estimation of serum calcium and phosphate can aid the diagnosis of bone diseases such as rickets.
Serum iron concentration is useful for the diagnosis of iron-deficiency anemia and diseases of iron overload such as hemochromatosis.
Estimation of serum urea, creatinine and uric acid are required for assessing renal ability to eliminate waste products.
Estimations of serum hormones have greatly improved medical care of endocrine diseases such as many cases of infertility.
Some general laboratory supplies:
Laboratory chemicals:
Chemicals are available in a variety of grades according to the degree of purity. There are chemicals of crude purity such as the commercial or industrial sulfuric acid that is used for batteries of cars. Reagent grade chemicals or analytical grade chemicals (analar) are usually used in clinical chemistry laboratory.
Centrifuges:
A centrifuge is a device to accelerate gravitational separation of substances differing significantly in their masses. In clinical laboratory centrifugation is used to separate particles from a solution in which they are suspended. Examples of this application are:
Removing cellular elements from blood to provide cell-free plasma or serum.
Concentration of cellular elements of biological fluids for the purpose of microscopic examination or chemical analysis.
Balances
Mass is an invariant property of matter while weight is a function of mass under the influence of gravity, a relation expressed by the equation:
Weight = mass × gravity
Two substances of equal weights and subject to the same gravitational force have equal masses. In practice, the terms mass and weight are used synonymously.
A single-pan balance is common in clinical lab. It is often electronically –operated and self-balancing. The operation of an electronic balance is very simple. It involves switching on the balance, placing a container on the balance pan to hold the material to be weighed, tarring off the weight of the container, transferring the material to be weighted to the container and recording the weight of the material from the digital display. A top-loading balance usually reads two decimals while an analytical balance reads four decimals.
Concept of solute and solvent
In clinical chemistry most measurements are concerned with the concentration of substances in solutions. The solution most often being blood, serum , urine, spinal fluid or other body fluids. The substance that is dissolved in a solution is a solute. Thus the compounds that are typically measured are solutes. In clinical chemistry, these are frequently referred to an analytes. The substance in which the solute is dissolved is a solvent. A solution is correctly defined as a physically homogenous mixture of two or more substances.
Standard solution: is a solution whose concentration is exactly known. It is prepared from highly purified chemicals that can be directly weighted or measured and dissolved in a known volume of a suitable solvent.
Units of concentration
The concentration of the solute in a solution may be expressed in different ways. Traditionally, in clinical chemistry lab., concentration is most often expressed as mass of solute per volume of solution, i.e., mass concentration (such as g/100mL or g% or mg/100 mL. or mg/dL or g/L). However, the system international (SI) recommends the use of moles of solute per volume of solution to express analyte concentration (i.e., Substance concentration ) wherever possible, and the use of liter as the reference volume (mol/L, mmol/L, or μ mol/l .).
Expression of volumes in clinical chemistry:
Most clinical biochemistry tests are nowadays done by using kits that are supplied by commercial companies. A kit is a package that contains all required reagents, and sometimes additional supplies, that are required to perform a certain test. So, the required samples are usually of small volumes and so are called micromethods or semi-micro methods. Such small volumes are expressed in the unit of microliter. One microliter is one part of million parts of liter or one part of a thousand parts of milliliter.
1 liter = 1000 milliliter ( ml ) =1000000 microliter ( µl )
1 liter = 1000 ml =1000000 µl QUOTE μl
1 liter = 10 dl
1ml = 1000 µl
1ml = 1 cubic centimeter (c.c)
1 µl = 0.001 ml or 10-3 ml, 1 µl = 10-6 liter
10 µl = 0.010 ml 100 µl = 0.1 ml , 500 µl = 0.5 ml
1 mol = 1000 mmol (millimoles)
1 mmol (10–3 mol) = 1000 μmol (micromoles)1 μmol (10–6 mol) = 1000 nmol (nanomoles)
1 nmol (10–9 mol) = 1000 pmol (picomoles)
Conversion from one set of units to another:
If a result is already expressed as mg/100 mL:Divide by the molecular weight of the solute (to convert from mg to mmol)
And multiply by 10 (to convert from 100 mL to a liter).
As an example the molecular weight of glucose is 180 and the molecular weight of urea is 60. A glucose concentration of 180 mg /100 ml and a urea concentration of 60 mg/100 ml are both equivalents of 10 mmol/L.
Some conversion factors:
To S I units
From S I units
Glucose
mg/dL/ 18=mmol/L
Mmol/L×18= mg/dL
Iron
μg/dL/5.6= μmol/L
μmol/L×5.6=g/dL
Urea
mg/dL/6=mmol/L
mmol/L×6=mg/dL
Uric acid
mg/dL/17= μmol/L
μmol/L×17=mg/dL
Cholesterol
mg/dL/39=mmol/L
mmol/L×39 mg/dL
Specimen collection and processing:
Chemical tests may be performed on:Whole blood such as in blood gases analysis
Or sometimes on plasma
Or urine,
Commonly the tests are performed on serum
Blood may be obtained by finger prick (in case of small volumes of whole blood) or by venipuncture and collected into either a plain tube (i.e., a tube which contains no anticoagulant and when clotted and centrifuged, a clear yellow fluid is collected which is the serum. If the blood is collected into a tube containing an anti-coagulant such as EDTA or heparin then it will not clot and this fluid blood when centrifuged will separate into cell layer in the bottom and turbid yellow fluid in the upper part which is the plasma which contains fibrinogen in addition to all constituents of serum.