How to Read Your Blood Test Report: Reference Ranges, H/L Flags and When to Worry

Quick answer: To read a blood test report, look at four columns for each test: the test name, your result, the unit (such as mg/dL or g/dL), and the reference range (the range seen in most healthy people). A result outside that range is usually marked H (high) or L (low). A small deviation is common and often not significant; what matters is how far outside the range it is, whether it fits your symptoms, and how it compares with your previous reports. Always review flagged results with your doctor.

Most people open their lab report on their phone, scroll to the first bold number, and search it online. That usually leads to unnecessary worry. A report is designed to be read in context — by you, with your doctor, alongside your symptoms and history.

Here's how to read one properly.

The Anatomy of a Lab Report

Every Aarvak report — and most lab reports in India — contains:

• Patient details: name, age, sex, sample ID and barcode. Always check these are yours.
• Sample details: sample type (serum, plasma, whole blood, urine), collection time and report time.
• Test name and method: for example, "Haemoglobin — photometric method". Different methods can give slightly different reference ranges.
• Result: your value.
• Unit: mg/dL, g/dL, mIU/L, ng/mL, cells/cumm and so on.
• Biological reference interval: the range found in about 95% of healthy people of your age and sex.
• Flag: H, L, or sometimes an asterisk or bold print for out-of-range values.
• Interpretation notes and signature: comments and the signature of the pathologist or authorised signatory.

What Does "Reference Range" Really Mean?

A reference range is built from healthy people. By definition, about 5% of perfectly healthy people fall slightly outside it on any given test. If you have 50 values on a full body checkup report, it is normal to see one or two flags that mean nothing clinically.

Reference ranges also:

• Differ between labs, because of different machines and methods — always compare your result with the range printed on the same report
• Differ by age and sex — haemoglobin, creatinine, ferritin and uric acid ranges are different for men and women
• Differ in pregnancy and childhood — TSH, ALP and blood counts have special ranges

How to Interpret H and L Flags

Ask three questions:

• How far outside the range is it? A haemoglobin of 11.8 g/dL against a lower limit of 12.0 is very different from 7.5 g/dL.
• Does it fit how I feel? A slightly low haemoglobin with breathlessness and fatigue matters more than the same value in someone who feels well.
• What did it look like last time? A trend is more meaningful than a single value. A creatinine slowly rising year after year deserves attention even if it is still "within range".

Common Reports Explained

Complete Blood Count (CBC)

Haemoglobin, RBC, WBC with differential, and platelets. Low haemoglobin suggests anaemia; high WBC suggests infection or inflammation; low platelets are important in dengue. Read our full CBC guide.

Blood Sugar and HbA1c

• Fasting sugar under 100 mg/dL is normal; 100–125 suggests pre-diabetes; 126 or above on two occasions suggests diabetes
• HbA1c under 5.7% is normal; 5.7–6.4% is pre-diabetes; 6.5% or above suggests diabetes

See HbA1c explained.

Lipid Profile

Total cholesterol, LDL ("bad"), HDL ("good") and triglycerides. Your target LDL depends on your heart risk, not just the printed range — a diabetic or heart patient's goal is lower. See our lipid profile guide.

Liver Function Test (LFT)

SGPT (ALT) and SGOT (AST) are enzymes; mild rises are common with fatty liver, alcohol, some medicines and even intense exercise. Bilirubin relates to jaundice. Read our LFT guide.

Kidney Function Test (KFT)

Creatinine and the calculated eGFR are the key numbers. eGFR estimates how well your kidneys filter. See our KFT guide.

Thyroid Profile

TSH is the main screening value. A high TSH usually means an underactive thyroid; low TSH can mean overactive. See our thyroid report guide.

Results That Need a Doctor Quickly

Labs call these "critical values". If your report shows something like the following, contact your doctor the same day:

• Very low haemoglobin (for example, below 7 g/dL)
• Very low platelets (for example, below 50,000/cumm), especially with fever or bleeding
• Very high or very low potassium or sodium
• Fasting blood sugar above 250–300 mg/dL, or below 60 mg/dL
• A sharp rise in creatinine compared with your previous report

At Aarvak, when a result falls in the critical range, our team contacts the patient or referring doctor directly rather than waiting for you to open the report.

Things That Can Affect Your Results

• Not fasting (or fasting too long) before sugar and lipid tests
• Heavy exercise in the 24 hours before the test (raises CK, SGOT, creatinine)
• Alcohol in the previous 24–48 hours
• Biotin supplements (can interfere with thyroid and some hormone tests — tell the lab)
• Dehydration (concentrates blood values)
• Poor sleep and acute illness
• Time of day (cortisol and some hormones vary through the day)

Read more in fasting before blood tests: myths debunked.

Frequently Asked Questions

What does H and L mean on a blood test report?

H means your result is above the laboratory's reference range and L means it is below. A flag is a prompt to review the value with your doctor, not a diagnosis.

Why are reference ranges different between labs?

Labs use different machines, reagents and methods, so each lab validates its own reference range. Always compare your result with the range printed on the same report.

Is a slightly abnormal blood test result something to worry about?

Often not. About 5% of healthy people fall slightly outside any reference range. Your doctor will consider how far out the value is, your symptoms and your previous results.

Can I compare reports from two different labs?

You can, but small differences may be due to method rather than a real change. For tracking a condition, it is best to use the same lab over time.

Who signs a lab report and why does it matter?

Reports should be reviewed and authorised by a qualified pathologist or authorised signatory. The signature confirms that the results have been checked before release.

How quickly are Aarvak reports available?

Most routine blood test and health package reports are available within 6–8 hours of sample collection. Specialised tests can take longer.

Get Clear, Doctor-Ready Reports From Aarvak

Aarvak's reports are barcoded from collection to result, follow NABL protocols, and are released after review. If you need help understanding your report, call +91 92663 33711. Ready to test? Browse health packages or book a test.

This guide is for general information. Interpretation of any result should be done by your doctor in the context of your health.