Clinical Biochemistry Overview

Purpose of Clinical Biochemistry

• Diagnosis of disease
• Prognosis - predict the clinical outcome of disease
• Screening for unknown clinical conditions
• Monitoring treatment, progress of chronic conditions, and effectiveness of treatment

Types of Samples for Biochemical Testing

• Blood (serum, plasma)
• Urine
• Faeces
• CSF
• Saliva
• Sweat
• Hair

Blood Collection Tubes

• Red/Yellow: Serum collection, contains clot activator, used for serum biochemistry, drug monitoring, and serum immunology tests.
• Lavender/Black: Whole blood collection, contains EDTA, used for hematology tests and ESR.
• Grey: Plasma collection contains sodium fluoride and potassium oxalate, use for glucose analysis and maintains original glucose and lactate concentrations.
• Light Blue: Plasma collection contains sodium citrate, used for coagulation tests.
• Green: Plasma collection contains lithium heparin, used for emergency biochemistry and plasma biochemistry tests.

Potassium Oxalate Use in Blood Glucose Analysis

• Anticoagulant that binds calcium ions

Sodium Fluoride Use in Blood Glucose Analysis

• Inhibits glycolysis
• Maintains the original glucose and lactate concentrations

Reference Interval for Normal Blood Glucose Concentration

• 4.0 - 6.0 mmole/L

### Spectrophotometric Ways of Measuring Blood Glucose Concentration

• Direct chemical reaction: Glucose reacts with a chemical to get a color change (e.g., dinitrosalicylic acid (DNS)).
• Enzyme-linked reaction: glucose oxidase oxidizes glucose and releases hydrogen peroxide; this reacts with o-Danisidine to give a colored product.

Analytical Sensitivity

• The smallest amount of the analyte that can be detected (detection limit).

Analytical Specificity

• How well an assay detects only a specific substance and does not detect closely related substances.

Accuracy

• How close the result comes to the true value.

Precision

• Reproducibility of multiple measurements.

Limits of Linearity

• A range of concentrations between which the result can be reported as accurate.

Regression Analysis

• Comparison of the output of two different assays, measuring a given analyte in the same samples.

Bland-Altman Plot (aka Difference plot)

• Indicates whether there is agreement between two assays.

Coefficient of Variation (CV) Calculation

• CV = (SD/mean) x 100

Detection Limit (Sensitivity)

• Lowest amount of analyte which can be distinguished from the absence of analyte.

Internal Quality Control

• Are the results today the same as yesterday?
• Quality control materials are manufactured with the analyte in question at various concentrations (H, M, L).
• QC materials are tested on the machine frequently each day, and after changing lamps, reagents, etc.
• Data is plotted on a Levy-Jennings Plot

Levy-Jennings Chart

• Indicates the performance of a test with quality control samples over time.

Levy-Jennings Plot - Trend

• 6 or more points show a consecutive move in the same direction.

Levy-Jennings Plot - Shift

• 6 or more results are on one side of the mean rather than scattered about the mean (i.e., the accuracy of the test has changed, the mean of the values is not the true value).

How Does Random Error Impact Accuracy and Precision?

• Accurate but imprecise (mean value = accurate)

How Does Systemic Error (Positive Bias) Impact Accuracy and Precision?

• Precise but inaccurate

External Quality Control

• Are the results the same as those of other labs performing the same test?
• Quality control samples are regularly sent to all labs.
• Performance Reports are generated.
• Assesses the performance of a lab.
• Compares the performance of the lab with other labs using the same analyzer and method.
• Compares against other analyzers and methods measuring the same analyte.

Precision? Bias?

• How reproducible are the results?
• Systematic difference to the true value.

Point of Care Testing

• Laboratory tests performed at or near a patient and at a site where care or treatment may be provided.

Therapeutic Drug Monitoring (TDM)

• Use of drug measurements in body fluids as an aid to patient management.

Standard Dose

• There is no standard dose because of differences in:
  • Absorption rates
  • Metabolism rates
  • Elimination rates

Causes of Differences in Absorption Rates

• Incorrect timing/method of taking tablets
• GI issues such as Coeliac Disease, Crohn's Disease, etc.

Explore the essential purposes and sample types used in clinical biochemistry. This quiz covers the importance of biochemical testing in disease diagnosis, prognosis, and monitoring treatment, as well as details on various blood collection tubes and their specific uses. Test your knowledge on a vital aspect of medical diagnostics.