Understanding Your Blood Test Results: A Plain-English Guide

You have had blood tests done and received a report full of abbreviations, numbers, and reference ranges. Here is what the most common markers actually mean, explained without medical jargon.

Full Blood Count (FBC) is the most commonly requested blood test. It counts the different types of cells in your blood. Haemoglobin (Hb) measures the oxygen-carrying protein in your red blood cells. Low haemoglobin (anaemia) can cause fatigue, breathlessness, and pale skin. The normal range is approximately 120-150 g/L for women and 130-170 g/L for men. White Blood Cell count (WBC) measures your immune cells. An elevated count often indicates infection or inflammation. A persistently low count may suggest bone marrow problems or immune suppression. Platelets are the cells responsible for blood clotting. Low platelets can lead to easy bruising and prolonged bleeding. High platelets may occur with infection, inflammation, or iron deficiency.

Kidney Function tests include creatinine and eGFR (estimated Glomerular Filtration Rate). Creatinine is a waste product from muscle metabolism, filtered by your kidneys. High levels suggest your kidneys are not filtering as efficiently as they should. eGFR estimates how well your kidneys are filtering. A normal eGFR is above 90 mL/min. Levels between 60 and 89 may indicate mild kidney impairment and warrant monitoring.

Liver Function Tests (LFTs) include several markers. ALT (alanine aminotransferase) and AST (aspartate aminotransferase) are enzymes released when liver cells are damaged. Elevated levels can indicate fatty liver disease, alcohol-related liver damage, viral hepatitis, or medication side effects. ALP (alkaline phosphatase) is elevated in conditions affecting the bile ducts or bone. Bilirubin is the yellow pigment from the breakdown of red blood cells. High bilirubin causes jaundice (yellowing of the skin and eyes). Albumin is a protein made by the liver. Low albumin can indicate chronic liver disease or malnutrition.

Thyroid Function includes TSH (Thyroid Stimulating Hormone) and Free T4. TSH is the most important initial test. High TSH suggests your thyroid is underactive (hypothyroidism), causing fatigue, weight gain, cold sensitivity, and low mood. Low TSH suggests overactivity (hyperthyroidism), causing weight loss, anxiety, rapid heartbeat, and heat intolerance. Free T4 measures the actual thyroid hormone in your blood.

Cholesterol Profile includes Total Cholesterol, HDL (the "good" cholesterol that removes fat from arteries), LDL (the "bad" cholesterol that deposits fat in arteries), and Triglycerides. Your cardiovascular risk is better assessed by the ratio of total cholesterol to HDL, rather than the total number alone. A ratio below 4 is considered good.

HbA1c measures your average blood sugar over the preceding 2 to 3 months. It is the gold standard for monitoring diabetes and detecting pre-diabetes. Below 42 mmol/mol is normal. 42 to 47 mmol/mol indicates pre-diabetes. 48 mmol/mol or above indicates diabetes. Fasting Glucose provides a snapshot of your blood sugar at a single point in time.

Vitamin D levels are worth knowing, particularly in the UK where deficiency is remarkably common due to limited sunlight exposure. Levels below 25 nmol/L are deficient. 25 to 50 nmol/L is insufficient. Above 50 nmol/L is adequate. Supplementation is straightforward and effective.

Iron Studies include Ferritin (the stored form of iron), Serum Iron, and Transferrin Saturation. Low ferritin is the most common cause of iron deficiency anaemia, particularly in women of childbearing age. Very high ferritin can indicate iron overload (haemochromatosis), inflammation, or liver disease.

A blood test result outside the reference range does not automatically mean something is wrong. Reference ranges represent the middle 95% of the population, meaning 5% of perfectly healthy people will have a result technically outside the range. Context matters: your age, sex, medications, recent illness, hydration status, and the trend over time all influence interpretation.

At Knightsbridge Doctors, we always discuss blood test results in detail during your consultation, explaining what each finding means for you specifically. If you have received blood test results that you do not fully understand, we welcome you to book a consultation for a thorough review. Call 020 7589 8965.