This document discusses the uses and types of clinical biochemistry investigations as well as quality control procedures. It notes that lab tests are used to confirm diagnoses, start treatment, screen for risk, monitor disease progression and response to therapy. Tests can be emergency, routine, special, or panels focusing on specific organs or metabolic processes. Quality control ensures accuracy, precision and error-free reporting through procedures like internal controls, reference ranges, and external quality assessments. Factors like specimen collection, transport, drugs, and physiology can influence test results.

1. CLINICAL
BIOCHEMISTRY
INVESTIGATIONS
Dr. S.Sethupathy
RMMC
AU

2. The uses of lab tests are:
 1. To confirm diagnosis - Serum CK-MB ,
Troponin-T
 2. To start rational treatment Example: High
serum LDL level
 3. To screen the people at risk.Ex: TSH
measurement in neonates

3. Uses
 4. To monitor the disease
progress.Example: Serum alanine
transaminase – hepatitis
 5. To monitor the responseto
therapy.Ex:Use of TSH measurement -
thyroxine.
 6. To explore the cause and mechanism of
the disease.- the genetic defect in cystic
fibrosis.

4. Types of Biochemical
investigations
 1. Emergency investigations: They are
available round the clock
 2.Stat tests: They are emergency
investigations and should be available
immediately
 3.Routine investigations: These tests are
done in batch mode

5.  4. Special investigations: These tests are
expensive, technically demanding Ex: hormone
assays
 5. Organ panels: Renal profile, liver profile,
lipid profile, thyroid profile.
 6. Metabolic workup and dynamic tests:
These are done under medical supervision.
.Ex: Breath tests, ADH stimulation test.

6. Types
 7. Point of care testing: These are available
at bedside especially ICU,OT etc.
 8. Molecular diagnostic tests: Referral
centers.Ex Gene expression profile using
microarray for cancer, Branched amino acids
analysis using mass spectrometry.

7. Quality control
 Quality control is done to maintain the quality
of the lab tests by assuring the accuracy ,
precision and error free reports for
appropriate
clinical judgment.

8.  Accuracy: It is the closeness of the
measured value with the true value.
 Precision:. It is the closeness among the
repeated measurements of the same sample.
 Precision is expressed as
coefficient of variation. CV= SD / mean x 100

10. Sensitivity
 It is the percentage of positive results in
patients with the disease.
 .Lab tests often have lower sensitivity in the
early stages of many diseases.
 In biochemical analysis, the lowest
concentration of the analyte - detected is
called the limit of detection.

11. Specificity
 It is the percentage of negative results among
people who do not have the disease. In
biochemical analysis, it may also indicate the
positive or negative interferences.

12.  The predictive value of a positive test or
positive predictive value is the percentage of
positive results that are true positives.
 Negative predictive value defines the
percentage of negative results that are true
negatives.

14.  Sensitivity = True positive(a) / Patients who
have the disease (a+c) x100
 Specificity = True negative (d) / patients who
do not have the disease (b+d) x 100

15.  Positive predictive value = True positive (a) /
total positive results (a+b) x 100
 Negative predictive value = True negative (d) /
total negative results (c+d) x 100

16. Interpretation of the results
 Normal values are generally considered to be
those that fall within 2 standard deviations.(+/-
2SD) of the mean value.
 .These ranges usually encompass 95% of the
selected population.

17. Methods
 Reference method: It is the most accurate
and specific method.It involves laborious
procedure using sophisticated equipment.
 Definitive method: It is adopted by the lab for
day to day service. It is technically less
demanding and usually closer to the reference
method.

18. Internal quality control
 It is done using control material available in
the laboratory to evaluate the quality of the
results.
 Control samples are commercially available in
low range (Low QC control ) and high
range(High QC control).

19. Levey Jennings chart
 The quality control sample is usually run daily
 the values are plotted on Levy Jennings chart.
 The concentration is plotted on the Y-
axis(Ordinate)
 the days are plotted on X-axis(abscissa).
 The blackline is the mean value.
 Blue line at 1SD , orange line at 2 SD and
redline at 3 SD
 If any deviation occurs beyond 2 SD , the test
is considered out of control.

21. Errors
 Random errors: They are caused by errors in
performing the test such as incomplete mixing
of reagents (Technical error) and fluctuations
in the electrical supply etc.
 Systematic errors: They are caused by the
changes in the reagent lot, changes in the
calibrator lot, deterioration of reagents and
deterioration of instruments.

22. Random errors

23. Systematic errors

24. External quality control
 Reference laboratory supplies the quality
control material
 the sample is analyzed without the knowing
the values.
 Evaluated by the reference laboratory .

25. VIS
 One of the methods is Variance index
score(VIS)
 Variance index score= % variation /coefficient
of variation x 100
 VIS – 0 is excellent, VIS – less than 100 is
Good, VIS – 100-150 is satisfactory and VIS
more than 250 is poor.

26.  Conventional units and SI units : SI units
(French – Systeme international d’ unites) is
the modern form of the metric system.
 Glucose in mg/dl is conventional unit
 Glucose in mmol/l is SI unit.

27. Factors influencing laboratory tests
 Physiological factors
 Fasting and fed state:Ex: Blood glucose
,triglycerides are affected by diet.
 Exercise: Increased serum levels of CK, LDH,
AST are seen after exercise.
 Diurnal variation: Ex:Cortisol is increased in the
morning. Growth hormone is increased during
night.

28.  Pregnancy:Altered sex hormones during
pregnancy, altered glucose tolerance in
pregnancy.
 Stress:Ex: ACTH, Cortisol, glucose levels are
affected in stress.
 Position of the patient: There is 6% increase
of values of plasma proteins,iron and
hormones in upright position.

29.  Drugs: Serum ALT level is increased by
rifampicin treatment. Serum uric acid level is
increased by thiazide diuretics.
 Specimen collection: Proper collection,
transport and storage is essential for good
laboratory practice.
 Preservatives:Anticoagulants such as
Heparin,EDTA,citrate, oxalate are used.
Fluoride inhibits glycolysis and it is used for
sample collection in blood glucose estimation.

30.  Vacutainer container tubes: They are used to draw
blood under vacuum for proper flow and volume
control.Gels are used to separate the cells from
plasma orserum.Color coding of tubes are helpful for
proper collection of the samples.
 Method of collection:Prolonged application of
tourniquet, flow of IV fluids in the arm of blood
collection will affect the tests. Avoiding hemolysis,
proper labeling of specimens are important.
 Transport: Pneumatic tubing system, electric tracks
are used in bigger hospitals for transport of the
samples to the lab.Storage under proper conditions
are also essential and frequent freezing and thawing
will affect the values.

31. Thank you