What are the most important markers in a blood test?

Blood tests are among the most widely used tools in medical diagnostics. By analyzing different components of the blood, healthcare professionals gain a snapshot of overall health. But which values are the most important? Here we review the key markers in a standard blood test and what they can reveal about your body.

Hemoglobin (Hb) – the body’s oxygen transporter

Hemoglobin is the protein in red blood cells that carries oxygen from the lungs to the rest of the body. Low hemoglobin levels may indicate anemia, which can result from blood loss, iron deficiency, or chronic disease¹. Elevated levels may occur with dehydration or bone marrow disorders.

White blood cells (Leukocytes) – the body’s defense system

White blood cells are a crucial part of the immune system. Their count can provide information about:

• Infections (high levels)

• Autoimmune diseases or blood disorders (abnormally low or high levels)²

A differential count can identify which types of white blood cells are affected.

Platelets (Thrombocytes) – for blood clotting

Platelets help blood clot following injury. Too few platelets can increase the risk of bleeding, while too many may raise the risk of blood clots³.

CRP (C-reactive protein) – an inflammation marker

CRP is a protein that rises in response to inflammation. Elevated CRP may indicate:

• Infections

• Autoimmune diseases

• Acute inflammation⁴

CRP is a quick and sensitive marker but does not reveal the cause on its own.

Blood glucose – the body’s energy level

Blood sugar levels are measured to assess risk for:

• Diabetes

• Hypoglycemia (low blood sugar) due to insulin issues or metabolic disorders

Long-term blood sugar (HbA1c) is also measured to evaluate blood sugar control over time.

Kidney function tests – creatinine and eGFR

Creatinine is a waste product normally filtered out by the kidneys. High levels may indicate impaired kidney function. Estimated glomerular filtration rate (eGFR), calculated from creatinine, provides a more accurate measure of kidney function⁵.

Liver enzymes – ALAT, ASAT, and ALP

These enzymes are found in liver cells. Elevated levels may indicate:

• Liver damage

• Inflammation

• Cholestasis (impaired bile flow)

Mildly elevated values can also occur after certain medications or intense physical activity.

Electrolytes – sodium, potassium, calcium

Electrolytes are essential for:

• Heart and muscle function

• Nerve signaling

• Fluid balance

Imbalances may result from dehydration, kidney disease, hormonal disorders, or medication use.

Iron status – ferritin and iron

Ferritin reflects the body’s iron stores. Low ferritin may signal iron deficiency, often before hemoglobin levels drop. High ferritin may be seen with inflammation, liver disease, or iron overload.

Summary

Blood tests provide vital information about health by assessing markers such as hemoglobin, white blood cells, platelets, CRP, glucose, kidney and liver function, electrolytes, and iron status. These values give clinicians important insights into oxygen transport, immune activity, organ function, and overall health.

References

1. Guyton AC, Hall JE. Textbook of Medical Physiology. 13th edition, Elsevier, 2016.

2. Bain BJ. Ethnic and sex differences in the total and differential white cell count and platelet count. J Clin Pathol. 1996.

3. Kaushansky K, et al. Platelets and megakaryocytes. In: Hematology: Basic Principles and Practice. 2018.

4. Pepys MB, Hirschfield GM. C-reactive protein: a critical update. J Clin Invest. 2003.

5. Stevens PE, Levin A. Evaluation and management of chronic kidney disease: synopsis of the KDIGO 2012 clinical practice guideline. Ann Intern Med. 2013.