L1+2 Clinical Chemistry

#type/lecture

Definition: Quantitative science concerning the measurement and determination of the amount of biologically important substances in body fluids

Accuracy + Reference interval / Medical decision level (MDL)

Accuracy & Precision

Accuracy: How close the measurement is to true value

closer to true value, more accurate

  • correct calibration

  • reliable methods

  • minimizing error

Precision: How close the measurement agree with each other

the closer each measurement is to each other, more precise

  • random error

  • instrument stability

  • consistency in experimental technique

Measurement error

Deviation between measured value and its true value

natural & unavoidable part of any experiment / test

  1. random error

  • unpredictable fluctuations

  • environmental variations

  • instrument sensitivity

  • slight procedural inconsistencies

  • affects precision - can be improved by averaging multiple readings

  1. Systematic Error

  • arises from consistent flaws

  • uncalibrated instruments

  • biases in procedures

  • flawed theoretical assumptions

  • skews all measurements in the same direction - affects accuracy

  • best measurements minimise both errors - to achieve both accuracy & precision

Reference Interval

a.k.a reference range

the range you see in eg. blood test report to show normal and abnormal

  • the range of value of a measured analyte in a group of healthy individuals (reference population)

  • derived by calculating the means and + - 2 standard deviations (upper and lower reference limit)

when creating reference internal need to make sure: confounding factors: time of day, gender, time of year, age

so that's why we have established age, sex and instrument-specific reference interval

Analyte

Any substance that is identified, quantified or characterized within an analytical procedure

it is considered a specific target of an investigation

can be in varying concentrations, physical, chemical or biological in nature

essential for diagnosis & management of diseases

(L1-CC)-Common-Analytes

Biological Specimen

any sample of biological material derived from living organisms: tissure, blood, whole organisms, or fluids that is collected and preserved for scientific study & analysis

preservation is important because the specimen will degrade cuz it is preserved in our body. biochemical properties will change. won't show the true properties of the patient

Blood

obtained from the peripheral vein or from the capillaries -> venous blood sample

plasma

  • coagulation studies

  • remove cellular portion because major components are there so it doesn't interfere with the test

cellular portion

  • used for complete blood count (CBC)

  • red blood cells, white blood cells & platelets

uncoagulated blood after centrifugation (with anticoagulant)

serum

  • obtained by centrifugation ( let the blood coagulate)

  • don't have coagulation factors (without anticoagulate)

  • contains electrolytes, hormones, antigens, antibodies, drugs, microbes, proteins

Urine

  • relatively easy to collect (why? cuz non invasive - won't cause patient pain like getting blood test)

  • to evaluate kidney function and the elimination of the waste product

! mid-stream / clean catch

  1. random urine ​- collected at any time ​- normal screening

  2. first morning urine ​- concentrated sample urine of urine that contains overnight accumulation of metabolities ​- for detection of proteins or unusual analytes

  3. 24-hour urine ​- collected over a full day ​- useful for comprehensive analysis of analytes that fluctuate throughout the day

🧠 Concepts Introduced

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