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the function of the clinical lab is

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to perform qualitative and quantitative analysis on body fluids such as blood, urine,and spinal fluid, as well as feces,tissue,calculi and other material

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Biochemical results are useful for

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diagnosis and treatment of disease

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Biochemical tests are used in

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diagnosis -prognosis -monitoring -screening

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Diagnosis:

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art or act of distinguishing one disease from another

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Medical diagnosis is based on

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the patient‟s history combined with the findings on examination.

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a differential diagnosis

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making a correct decision between diseases presenting a similar clinical picture

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Biochemical tests are important for

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confirmation or rejection of clinical diagnosis

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Prognosis:

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medical term indicates the doctor's prediction of how a patient's disease will progress, and whether there is chance of recovery

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based on what the prognosis

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knowledge of the course of the disease in other patients together with the general health, age and sex of the patient

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serial measurements of plasma creatinine concentration in progressive renal disease are used to indicate when dialysis may be required example on what?

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Tests used primarily for diagnosis may also provide prognostic information

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major use of biochemical tests

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1- follow the course of an illness 2- monitor the effects of a treatment

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Monitoring (sequential recording, keep watch over)

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there should be a suitable analyte, for instance, glucose in patients with diabetes mellitus

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In clinical chemistry, most measurements are concerned with the concentrations of substances

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in solutions, the solutions most often being blood, serum,urine, spinal fluid, or other body fluid. The substance that is dissolved in a solution is a solute or analytes.

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Biochemical tests may also be used to detect complications of treatment, such as

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hypokalemia during treatment of diuretics

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Screening (examine for the presence or absence of a disease)

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to determine Subclinical diseases: An illness that stays below the surface of clinical detection, which has no recognizable clinical findings .

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the best known example of screening is

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mass screening of all new born babies for phenylketonuria, which is carried out in many countries.

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The clinical biochemistry tests can be divided into three main category

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1- Core biochemistry 2- Specialized tests 3- The emergency lab

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Core biochemistry

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are the commonly requested tests which are of value in many patients, on frequent basis.

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Specialized tests

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Not every lab is equipped to carry out all possible biochemistry requests. Less commonly asked tests for.

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The emergency lab

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All clinical biochemistry labs provide facilities for urgent tests. Only a small number of test types are available from the emergency lab. These tests are processed rapidly. An urgent test is designed as test on which the clinician is likely to take immediate action.

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Core biochemical tests

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Sodium, potassium, chloride and bicarbonate Urea and creatinine Calcium and phosphate Total protein and albumin Bilirubin and alkaline phosphatase ALT and AST-glutamyl transpeptidase Creatinine kinase H+, PCO2, and PO2(blood gases) GlucoseAmylase

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Specialized tests

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Hormones Specific proteins Trace elements Vitamins Drugs Lipids and lipoproteins DNA analysis

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Emergency tests

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Urea and electrolytes Blood gases Amylase Glucose Salicylates Paracetamol Calcium

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major specimens analyzed

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Blood • Urine • Cerebrospinal Fluid

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Choice of specimen type depends on

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- Analyte to be measured - Ease of collection

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Source of blood

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- Veins - Arteries - Skin puncture-capillary blood

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Collection Method of blood

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- Syringe - Evacuated tube • Additives • Separator gel - Intravenous lines

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Factors affecting choice of Blood Source and Collection Method

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- Analyte under investigation - Patient • vascular status • ease of collection

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__________ s usually the specimen of choice

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Venous blood

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Skin puncture

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only a small volume of blood is required for a blood test (e.g., a blood glucose test)

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• A skin puncture may be used to obtain the sample in

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an infant younger than 1 year, the lateral or medial plantar surface of the foot should be used for skin puncture

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Whole blood needed for testing

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anticoagulant must be added to the specimen during the collection procedure. Whole blood is rarely required for clinical chemistry tests; only for blood gas, ammonia, and some trace element determinations

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Plasma needed for testing

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Plasma is the fluid fraction of blood. If plasma is desired for testing, an anticoagulant must be added to the specimen during the collection procedure

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Serum needed for testing

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Serum is the supernatant fluid which forms when blood clots

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plasma

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Plasma is fluid component of blood. Comprises ~55% of total volume ofwhole blood. Contains proteins, sugars, vitamins,minerals, lipids, lipoproteins And clotting factors. 95% of plasma is water

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If blood is collected and allowed to stand it will clot. Formation of an insoluble fibrin clot. If blood is then centrifuged the fluid portion is known as

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SERUM

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If blood is collected into a plain tube and allowed to clot after centrifugation what it will produce?

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serum specimen is obtained

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Serum from coagulated blood is the specimen of choice for many assay systems, but plasma

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obtained with an appropriate anticoagulant may be an equally valid specimen.

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The use of plasma accelerates

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analysis in medical emergencies and when the analyte is unstable.

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why not serum for emergency?

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Because serum requires a wait of 15 to 30 min for coagulation

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Plasma yield from a given volume of whole blood is _______ than the yield of serum

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is always greater (15 to 20 % more in volume of plasma than of serum can be isolated from the same volume of blood).

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The formation of fibrin clots or fragments when plasma is stored and the subsequent risk of

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blockage sample probes of automated analytical instruments is a disadvantage

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Plasma is also not suitable for

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electrophoretic analysis, because the presence of fibrinogen can confuse interpretation of electrophoretic patterns

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Blood specimen tubes for specific biochemical tests like?

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Serum separator tube (SST) contains a gel at the bottom to separate serum

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The type of urine to be collected is determined by

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the tests to be performed.

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the most concentrated specimen and thus is preferred for microscopic examinations.

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clean, early-morning, fasting specimen

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It is satisfactory in most cases to use specimen collected with

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careful attention to cleanliness and to keeping the urine cool.

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Collection of urine is preferred to be

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fresh, no need for preservatives. But 24 hour urine sample, must introduce a preservative.

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The most common preservatives in urine collection

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freeze, glacial acetic acid nitric acid

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Preservatives have different roles but are usually added to

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reduce bacterial action or chemical decomposition or to solubilize constituents that might otherwise precipitate out of solution

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Collection of faeces

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to detect the presence of "hidden" or so called occult blood, which is recognized as one of the most effective evidences to the presence of bleeding ulcer or a malignant disease in the GIT

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Collection of spinal fluid

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Spinal fluid is normally obtained from the lumbar region. Spinal fluid is examined when there is a question as to the presence of meningitis

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Synovial fluid aspiration

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synovial fluid is withdrawn from joints to aid characterization of the type of arthritis and to differentiate non-inflammatory from

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SAMPLING ERRORS

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There are a number of potential errors which may contribute to the success or failure of the laboratory

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Blood Sampling technique

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Difficulty in obtaining a blood specimen may lead to haemolysis with consequent release of potassium and other red cell constituents. Results of these tests will be falsely elevated.

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Prolonged stasis during vein puncture:

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Plasma water diffuses into the interstitial space and the serum or plasma sample obtained will be concentrated. Proteins and protein-bound components of plasma such as calcium or thyroxine will be falsely elevated.

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Insufficient specimen:

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analysis requires certain volume of specimen to enable the test to be carried out

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Error in timing:

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The biggest source of error in the measurement of any analyte in a 24-hour urine specimen is in collection of an accurately timed volume of urine.

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•Incorrect specimen container:

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for each blood sample, the correct container with the proper anticoagulant should be used

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Samples for glucose

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should be collected into a special container containing fluoride which inhibits glycolysis

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If a sample is collected into the wrong container

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it should never be decanted into another type of tube. For example, blood which has been exposed to EDTA (an anti-coagulant used in sample containers reduced calcium concentration approaching zero.

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•Inappropriate sampling site:

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Blood samples should not be taken 'downstream„ from an intravenous drip. e.g Blood sample for glucose taken from the same arm into which 5%, glucose is being infused.

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•Incorrect specimen storage

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A blood sample stored long time before analysis show falsely high potassium, phosphate and RBC enzymes as lactate dehydrogenase

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Biochemical test results are usually compared to a

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reference range considered to represent the normal healthy state

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Most reference ranges are chosen randomly to include

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95% of the values found in healthy volunteers by definition 5%, of the population will have a result out of reference range.

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no rigid limits to separate the diseased population from the healthy. T OR F

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T

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Biological factors affecting the interpretation of results

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• Sex of the patient. • Age of the patient. • Effect of diet. • Time when sample was taken. • Stress and anxiety. • Posture of the patient. • Effects of exercise. • Medical history. • Pregnancy. • Drug history.

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Time when sample was taken:

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• Many constituents of body fluids exhibit cyclical variations (Circadian variation); throughout the day: occurring in 24-hour periods. • These cyclical variations may be quite large the drawing of specimen must be strictly controlled. • The concentration of serum iron, may change by as much as 50% from 08:0 to 14:0 hours, and that of cortisol may change by a similar amount between 08:0 and 16:0.

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Posture of the patient.

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• The blood volume of an adult in an upright position is typically 600 to 700 ml less than that of an adult in lying down position. • Changes from a lying to an upright position associates to reduction of about 10% in the blood volume.

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Posture of the patient. (2)

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• Fluid reduction in plasma is associated with a comparable increase in the plasma protein concentration. • The concentrations of all proteins, including enzymes and protein hormones, and of such compounds as drugs, calcium and billirubin, which circulates partly bound to protein, are also affected.

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Sodium

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135-145 mmol/L

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Potassium

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3.5-5.0 mmol/L

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Calcium

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2.2-2.6 mmol/L

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Phosphate

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0.8-1.4 mmol/L

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Glucose

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2.8-6.0 mmol/L

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Urea

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3.3-6.7 mmol/L

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Creatinine

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60-120 mol/L

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Albumin

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30-50g/L

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Total protein

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60-80 g/L

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Bilirubin

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3-20 mol/L

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AST

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10-50 IU/L

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ALP

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30-150 IU/L

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GGT

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0-60 IU/L

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Total cholesterol

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140-200 mg/dl

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HDL cholesterol

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29-60 mg/dl

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