Biomarkers are measurable indicators of biological states that can be used to assess health, disease risk, and response to treatment. They include physiological measures like blood pressure as well as molecular indicators in blood and tissues. Biomarkers must be easy to obtain, provide rapid results accurately, and have good sensitivity and specificity to be useful for clinical purposes like diagnosis or monitoring disease progression and response to interventions. They provide objective assessments but also have disadvantages like expense and storage challenges.

2. Definition
Biomarkers are the measures used to perform a clinical assessment such as blood
pressure or cholesterol level and are used to monitor and predict health states in
individuals or across populations so that appropriate therapeutic intervention can be
planned.
Biomarkers may be used to assess the health or disease state of an individual.
Generally, Biomarker can be defined as a characteristic that is objectively measured
and evaluated as an indicator of normal biological processes, pathogenic processes,
or pharmacologic responses to a therapeutic intervention.

3. WHO has stated that a true definition of biomarkers includes "almost any measurement
reflecting an interaction between a biological system and a potential hazard, which may
be chemical , physical, or biological. The measure response may be functional and
physiological, biochemical at the cellular level, or a molecular interaction" Examples of
biomarkers include everything from pulse and blood pressure through basic chemistries
to more complex laboratory tests of blood and other tissues.
In medicine, a biomarker is a measurable indicator of the severity or presence of some
disease state.
For example, body temperature is a well-known biomarker for fever. Blood pressure is
used to determine the risk of stroke. It's also widely known that cholesterol values are a
biomarker and risk indicator for coronary and vascular disease, and that C-reactive
protein (CRP) is a marker for inflammation.

4. A wide range of biomarkers are used today . every biological system has it's own
specific biomarkers.
General health check may include assessment of blood pressure, heart rate,
cholesterol, triglycerides and fasting glucose levels. Body measurement such as
weight, body mass index (BMI), and waist-to-hip ratio are routinely used for
assessing conditions such as obesity and metabolic disorders.

5. Disease related biomarkers and drug-related biomarkers
It's necessary to distinguish between disease-related and drug-related biomarkers.
Disease-related biomarkers give an indication of the probable effect of treatment on
patient (risk indicator or predictive biomarkers ), if a disease already exists
(diagnostic biomarkers) , or how such a disease may develop in an individual case
regardless of the type of treatment (prognostic biomarker). Predictive biomarkers
help to assess the most likely response to a particular treatment type, while
prognostic markers shows the progression of disease with or without treatment. In
contrast, drug-related biomarkers indicate whether a drug will be effective in a
specific patient and how the patient's body will process it.
In the past, biomarkers were primarily physiological indicators such as blood
pressure or heart rate. More recently, biomarker is becoming a synonym for
molecular biomarker, such as elevated prostate specific antigen as a molecular
biomarker for prostate cancer.

6. Biomarker Requirements
1. In order to use a biomarker for diagnostics, the sample material must be as easy
to obtain as possible.
2. The speed with a result is obtained from the biomarker test is critical (rapid test).
3. Biomarker must be accurate and as easy to carry out as possible.
4. A biomarker for clinical use needs good sensitivity and specificity e.g ≥ 0.9.

7. Biomarker Classification
A- Based on their characteristics
1- Imaging biomarkers (CT, PET, MRI)
2- Molecular biomarkers ( biophysical properties in biological samples)
B- Classified based on their application
1- Physiological biomarker e.g pregnancy test
2- Diagnostic biomarkers e.g Cardiac troponin for the diagnosis of myocardial infraction
3- Staging of disease biomarkers e.g Chronic kidney disease ( End stage renal failure )
4- Disease prognosis biomarkers e.g Cancer biomarkers
5- Biomarkers for monitoring the clinical response to an intervention
e.g HbA1C for anti-diabetic treatment

9. Technical Validation of Biomarker
 Accuracy ( agreement with a reference)
 Precision ( repeatability, reproducibility)
 Limit of Detection ( sensitivity )
 Interference , Cross-reactivity ( specificity)
 Sample preparation / conditions.
 Performance around the cut-off
 Potential for carryover, cross-hybridization

10. Biomarker
Advantages Disadvantages
 Objective assessment
 Precision of measurement
 Reliable, validity can be
established.
 Less biased than questionnaires
 Disease mechanism often
studied.
 Homogeneity of risk or disease
 Timing is critical
 Expensive ( cost for analysis)
 Storage ( longevity of samples)
 Laboratory errors
 Normal range difficult to
establish
 Ethical responsibility