Blood Investigations to Order

This document provides a concise guide to common blood investigations, outlining their purpose and clinical significance. It serves as a quick reference for healthcare professionals to aid in selecting appropriate blood tests for various clinical scenarios. The information presented is intended for guidance only and should not replace clinical judgment or specialist consultation.

Complete Blood Count (CBC)

The CBC is a fundamental blood test that provides a comprehensive overview of the cellular components of blood. It includes:

• Red Blood Cell (RBC) Count: Measures the number of red blood cells, essential for oxygen transport. Abnormalities can indicate anemia or polycythemia.
• Hemoglobin (Hb): Measures the amount of hemoglobin in the blood, the protein in red blood cells that carries oxygen. Low levels indicate anemia.
• Hematocrit (Hct): Measures the percentage of blood volume occupied by red blood cells. It is also used to assess anemia or polycythemia.
• Mean Corpuscular Volume (MCV): Measures the average size of red blood cells. Helps classify anemia as microcytic, normocytic, or macrocytic.
• Mean Corpuscular Hemoglobin (MCH): Measures the average amount of hemoglobin in each red blood cell.
• Mean Corpuscular Hemoglobin Concentration (MCHC): Measures the average concentration of hemoglobin in each red blood cell.
• Red Cell Distribution Width (RDW): Measures the variation in the size of red blood cells. Elevated RDW can indicate early iron deficiency or other anemias.
• White Blood Cell (WBC) Count: Measures the total number of white blood cells, which are crucial for immune function. Elevated levels can indicate infection, inflammation, or leukemia. Low levels can indicate immune deficiency or bone marrow suppression.
• Differential WBC Count: Determines the percentage of each type of white blood cell (neutrophils, lymphocytes, monocytes, eosinophils, and basophils). Helps identify the specific cause of an elevated or decreased WBC count.
• Platelet Count: Measures the number of platelets, which are essential for blood clotting. Low levels (thrombocytopenia) can increase the risk of bleeding, while high levels (thrombocytosis) can increase the risk of clotting.
• Mean Platelet Volume (MPV): Measures the average size of platelets.

Electrolytes

Electrolyte panels measure the levels of key electrolytes in the blood, which are essential for maintaining fluid balance, nerve function, and muscle function.

• Sodium (Na+): Important for fluid balance, nerve function, and muscle function. Abnormal levels can indicate dehydration, overhydration, or hormonal imbalances.
• Potassium (K+): Crucial for nerve and muscle function, especially heart function. Abnormal levels can cause arrhythmias.
• Chloride (Cl-): Works with sodium to maintain fluid balance and blood pressure.
• Bicarbonate (HCO3-): Helps regulate blood pH. Abnormal levels can indicate metabolic or respiratory disorders.
• Calcium (Ca2+): Important for bone health, nerve function, muscle function, and blood clotting.
• Magnesium (Mg2+): Important for nerve and muscle function, blood sugar control, and blood pressure regulation.
• Phosphate (PO43-): Important for bone health, energy production, and nerve and muscle function.

Renal Function Tests (RFTs)

RFTs assess the function of the kidneys.

• Creatinine: A waste product filtered by the kidneys. Elevated levels indicate impaired kidney function.
• Blood Urea Nitrogen (BUN): Another waste product filtered by the kidneys. Elevated levels can also indicate impaired kidney function, dehydration, or high protein intake.
• Estimated Glomerular Filtration Rate (eGFR): A calculation based on creatinine, age, sex, and race that estimates the rate at which the kidneys filter blood. A low eGFR indicates impaired kidney function.
• Uric Acid: Elevated levels can indicate gout or kidney disease.

Liver Function Tests (LFTs)

LFTs assess the function of the liver.

• Alanine Aminotransferase (ALT): An enzyme found primarily in the liver. Elevated levels indicate liver damage.
• Aspartate Aminotransferase (AST): Another enzyme found in the liver and other tissues. Elevated levels can indicate liver damage or muscle damage.
• Alkaline Phosphatase (ALP): An enzyme found in the liver, bones, and other tissues. Elevated levels can indicate liver disease, bone disease, or bile duct obstruction.
• Bilirubin: A waste product produced by the breakdown of red blood cells. Elevated levels can indicate liver disease, bile duct obstruction, or hemolytic anemia.
• Albumin: A protein produced by the liver. Low levels can indicate liver disease, kidney disease, or malnutrition.
• Total Protein: Measures the total amount of protein in the blood.

Coagulation Studies

Coagulation studies assess the blood’s ability to clot.

• Prothrombin Time (PT): Measures the time it takes for blood to clot. Used to monitor warfarin therapy and assess liver function.
• International Normalized Ratio (INR): A standardized ratio of PT results, used to monitor warfarin therapy.
• Partial Thromboplastin Time (PTT): Measures the time it takes for blood to clot. Used to monitor heparin therapy and assess clotting factor deficiencies.
• Fibrinogen: A protein essential for blood clotting. Low levels can increase the risk of bleeding.
• D-dimer: A protein fragment produced when blood clots break down. Elevated levels can indicate a blood clot, such as deep vein thrombosis (DVT) or pulmonary embolism (PE).

Cardiac Markers

Cardiac markers are used to assess heart damage.

• Troponin: A protein released into the blood when the heart muscle is damaged. Elevated levels indicate a heart attack (myocardial infarction).
• Creatine Kinase-MB (CK-MB): Another enzyme released into the blood when the heart muscle is damaged.

Lipid Profile

A lipid profile measures the levels of cholesterol and triglycerides in the blood.

• Total Cholesterol: Measures the total amount of cholesterol in the blood.
• High-Density Lipoprotein (HDL) Cholesterol: “Good” cholesterol that helps remove cholesterol from the arteries.
• Low-Density Lipoprotein (LDL) Cholesterol: “Bad” cholesterol that can build up in the arteries and increase the risk of heart disease.
• Triglycerides: A type of fat in the blood. Elevated levels can increase the risk of heart disease.

Thyroid Function Tests (TFTs)

TFTs assess the function of the thyroid gland.

• Thyroid-Stimulating Hormone (TSH): A hormone produced by the pituitary gland that stimulates the thyroid gland to produce thyroid hormones. Elevated levels indicate hypothyroidism (underactive thyroid), while low levels indicate hyperthyroidism (overactive thyroid).
• Free Thyroxine (Free T4): The active form of thyroid hormone.
• Free Triiodothyronine (Free T3): Another active form of thyroid hormone.

Glucose

• Fasting Blood Glucose: Measures blood glucose levels after an overnight fast. Used to diagnose diabetes.
• Hemoglobin A1c (HbA1c): Measures average blood glucose levels over the past 2-3 months. Used to monitor diabetes control.
• Oral Glucose Tolerance Test (OGTT): Measures blood glucose levels at intervals after drinking a sugary drink. Used to diagnose gestational diabetes.

Inflammatory Markers

• C-Reactive Protein (CRP): A protein produced by the liver in response to inflammation. Elevated levels can indicate infection, inflammation, or autoimmune disorders.
• Erythrocyte Sedimentation Rate (ESR): Measures the rate at which red blood cells settle in a test tube. Elevated levels can indicate inflammation.

Other Investigations

• Amylase and Lipase: Enzymes used to diagnose pancreatitis.
• Vitamin B12 and Folate: Used to diagnose anemia and neurological disorders.
• Iron Studies: Includes serum iron, ferritin, transferrin, and total iron-binding capacity (TIBC). Used to diagnose iron deficiency anemia.
• Blood Cultures: Used to detect bacteria or other microorganisms in the blood.
• Arterial Blood Gas (ABG): Measures the levels of oxygen and carbon dioxide in the blood, as well as blood pH. Used to assess respiratory and metabolic disorders.

This list is not exhaustive, and other blood investigations may be necessary depending on the clinical situation. Always consider the patient’s history, physical examination findings, and other diagnostic tests when ordering blood investigations.