During home medical care, a doctor will often request a small group of blood tests to check for infection, anaemia, kidney function, blood sugar or the effects of medicines. This guide explains in general terms what these common tests are for — and why a result outside the printed range does not always mean something is wrong.
Each result on a report is usually shown next to a reference range. This range describes where results fall for most healthy people tested by that laboratory, but by definition a small proportion of healthy people will have results outside it. Ranges also vary between laboratories and methods, and some depend on age, sex or pregnancy.
A result is therefore a piece of evidence, not a diagnosis. A doctor considers how far outside the range it is, whether it has changed compared with previous results, and whether it fits the patient's symptoms and other findings. This is why this guide explains what tests are for, rather than listing numbers.
This test measures the different types of blood cells. The haemoglobin level helps detect anaemia. The white cell count and its components can suggest infection, inflammation or other conditions. The platelet count is important in conditions such as dengue and when patients take certain medicines. See the detailed guide to the full blood count.
C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) rise when there is inflammation or infection somewhere in the body. They do not show where the problem is, but a doctor may use them to judge severity or whether a patient is responding to treatment. CRP changes more quickly than ESR.
Serum creatinine and the calculated eGFR estimate how well the kidneys are filtering the blood. Electrolytes — especially sodium and potassium — are closely controlled by the kidneys and can be affected by dehydration, vomiting, diarrhoea, and medicines such as diuretics and some blood pressure tablets. These tests are among the most important for patients who are unwell at home, older, or on several medicines. See our guides to the renal profile and serum electrolytes.
A fasting or random blood glucose shows the sugar level at the time of the test. HbA1c reflects average blood sugar over the previous two to three months and is used to monitor diabetes control. The two answer different questions, and a doctor may request one or both.
This group of tests includes liver enzymes, bilirubin and albumin. Abnormal results may reflect liver inflammation, bile flow problems, medicine effects, alcohol, or conditions elsewhere in the body. Albumin can also be low in people who are unwell or poorly nourished. Detailed explanations are in our liver profile guide.
The thyroid-stimulating hormone (TSH) test is commonly used to check thyroid function and to adjust thyroid medicine doses. Results can be temporarily affected by acute illness, so a doctor may repeat the test after recovery.
Although not a blood test, a urine full report is often requested alongside blood tests to look for signs of infection, blood or protein in the urine. Results should be interpreted with symptoms: bacteria or white cells in the urine of an older person without symptoms do not always need treatment.
Do not start, stop or change treatment on the basis of a report alone, and avoid searching for a diagnosis from individual numbers. Bring the report to the doctor who requested it, together with the patient's medicine list and previous results.
Laboratories usually contact the requesting doctor directly if a result is dangerously abnormal. If you are told that a result needs urgent attention, or if the patient is becoming more unwell while waiting for results, seek medical care promptly. In an emergency in Sri Lanka, call 1990 Suwa Seriya for an emergency ambulance, or seek immediate care at an appropriate hospital.
Sineth Hospitals' English Health Education investigations library contains detailed explanations of individual tests.
Published by: Sineth Hospitals
Medically reviewed by: Dr. Seneth Gajasinghe, MBBS (Colombo), MD (Colombo), Medical Director, Sineth Hospitals
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Do not diagnose yourself or change treatment based on a report. Results need to be interpreted by a doctor who knows the full clinical picture.
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