Units on Indian lab reports: mg/dL, mmol/L and how to convert them

Why units matter more than you think

Every laboratory result has two parts: a number and a unit. The unit tells you what the number is counting. “5.6” could be a perfectly normal blood glucose in one unit and a dangerously low one in another. A result is only meaningful when you know which unit goes with it.

The problem is that there are two common systems. Laboratories in India, the United States and a few other countries usually report many chemistry tests as a mass per volume, such as milligrams per decilitre (mg/dL). Most of the rest of the world, including the UK, Europe, Canada and Australia, uses the international system (SI), which reports amounts of substance, such as millimoles per litre (mmol/L). Each country has its own mix, and some tests are customarily reported the same way everywhere.

Because patients now read international health sites, travel for treatment, bring reports from abroad and use phone apps, they meet both systems. Clinics receiving reports from different laboratories do too. Understanding the conversion removes much confusion.

Why a conversion is not just one number

Converting between mass and amount of substance depends on the weight of the molecule being measured. Glucose, cholesterol and creatinine are different molecules, so each has its own factor. You cannot apply the glucose factor to cholesterol. The general rule is:

mmol/L = (mg/dL × 10) ÷ molecular weight in g/mol (multiply by 1,000 for µmol/L), which is why the factors below differ.

All conversions in this guide are rounded, and a laboratory may round slightly differently, so small differences in the last digit are normal.

The conversion table

Two further conversions are specific to Indian reports. White cell counts are often printed per cubic millimetre (/cumm), and cubic millimetre equals one microlitre, so 7,800 /cumm is 7.8 ×10^9/L. Platelets are printed in lakhs per cubic millimetre, so multiply by 100 to get ×10^9/L: 2.4 lakh/cumm is 240 ×10^9/L.

Some tests need no conversion between systems: TSH in mIU/L and µIU/mL are the same number, and enzymes such as ALT and AST are reported in U/L (or IU/L) in both systems.

Worked examples (example values)

Each example below uses made-up numbers and shows the formula so that you can repeat it with a calculator.

• Glucose: a fasting glucose of 126 mg/dL: 126 ÷ 18.0 = 7.0 mmol/L. Going the other way, 5.6 mmol/L × 18.0 = about 101 mg/dL.
• Total cholesterol: 200 mg/dL ÷ 38.67 = 5.17, which rounds to 5.2 mmol/L. An LDL of 100 mg/dL is 2.6 mmol/L.
• Triglycerides: 150 mg/dL ÷ 88.57 = 1.69, which rounds to 1.7 mmol/L. Note that using the cholesterol factor here would give 3.9, which is wrong by more than double.
• Creatinine: 1.1 mg/dL × 88.4 = 97.2, so about 97 µmol/L. A report from another country showing 110 µmol/L equals 110 ÷ 88.4 = 1.24 mg/dL.
• Urea and BUN: a BUN of 14 mg/dL × 0.357 = 5.0 mmol/L of urea; the same blood would show a urea of 14 × 2.14 = about 30 mg/dL on an Indian report that reports urea rather than BUN.
• Bilirubin: 1.2 mg/dL × 17.1 = 20.5 µmol/L.
• Haemoglobin: 11.5 g/dL × 10 = 115 g/L.
• Vitamin D: 20 ng/mL × 2.5 = 50 nmol/L, and 75 nmol/L ÷ 2.5 = 30 ng/mL.
• HbA1c: at 7.0 %, (7.0 − 2.15) × 10.929 = 53 mmol/mol. Going back, mmol/mol × 0.09148 + 2.152 = %, so 64 mmol/mol is about 8.0 %.

Why you must never compare numbers across units

It is tempting to read an article that says “normal glucose is below 5.6” and compare it with a report that says 98. Both statements can be right, because one is in mmol/L and the other in mg/dL, and 98 mg/dL equals 5.4 mmol/L. The risks of mixing units are real:

• False alarm: reading a creatinine of 97 µmol/L as though it were mg/dL would suggest severe kidney failure when the kidneys may be normal, and reading a glucose of 7.0 mmol/L as though it were mg/dL would suggest dangerously low blood sugar.
• False reassurance: a triglyceride value of 2.2 mmol/L (about 195 mg/dL) looks tiny beside a rule of thumb such as “normal is below 150”, so a high result could be wrongly dismissed.
• Wrong trends: comparing a report from last year in one unit with this year’s in another can invent an improvement or a worsening that did not happen.
• Wrong targets: a target quoted in mmol/L (for example for glucose or LDL) applies to a result in mmol/L only. The same target in mg/dL is a very different number.

The reference range printed on a report belongs to the unit printed on that report. Do not borrow a range from another source unless you convert it with the correct factor, and even then the range may not fit your laboratory’s method.

Other reasons two numbers differ

Even when units agree, results from different laboratories may not match exactly. Methods and instruments differ, samples may be taken at different times or after different preparation, and reference intervals are set separately by each laboratory. Our guide to reading a laboratory report explains why the same person can have slightly different numbers in two places. HbA1c has an extra complication: it can be reported on two scales (the NGSP percentage and the IFCC mmol/mol scale) that are not simply a unit change but a formula, as described in our guide to understanding HbA1c results.

Where conversions most often cause trouble

In practice, a few situations account for most of the confusion.

• Reports from abroad or from a patient who has moved: a creatinine of 80 and a glucose of 5.2 look like different tests until you notice they are in µmol/L and mmol/L.
• Health apps and wearables, which may default to mmol/L or to mg/dL depending on where they were set up. Check the setting before you enter a value.
• Online calculators that ask for “cholesterol” without saying which unit they expect. Read the label of each box before entering numbers.
• Medical papers and guidelines, which often quote targets in SI units. Convert the target, not just your own value.

A checklist for every report

Before you interpret any number, run through these steps:

1. Find the unit next to each result. If it is missing, ask the laboratory. 2. Find the reference range for that unit on the same line. 3. Check whether the unit is the one you expected. If a number looks surprising, the unit is the first thing to check. 4. If you are comparing two reports, confirm both use the same unit and, ideally, the same laboratory. 5. If you convert, write down the formula and the rounding, and check the answer against the printed range. 6. For prescriptions, never convert doses yourself. Medicine strengths such as mg and mcg (micrograms) are different units, and a mix-up of a thousand-fold is dangerous. Ask the pharmacist if the label or prescription is unclear. 7. Ask your doctor about anything you cannot reconcile, instead of guessing.

Tips for clinics and record-keepers

Clinics that receive reports from many laboratories should store the unit with every result and never strip it out, to avoid a number that looks consistent but is not. When entering values into any system, record the unit exactly as printed, and convert only with the documented factor, noting the original. Where a trend chart combines results from different laboratories, ensure it plots one unit throughout.

Questions worth asking your doctor or laboratory

• Which unit does this report use, and is it the same as my previous one?
• Can the next report show both units?
• Is my previous result from another laboratory comparable with this one?
• Which range should I use for my age and sex?

Sources

• Testing.com: Reference ranges and what they mean — why ranges and units differ between laboratories
• MedlinePlus: Blood Glucose Test — glucose results and units
• MedlinePlus: Cholesterol Levels — cholesterol categories in mg/dL
• American Diabetes Association: Understanding A1C — HbA1c and estimated average glucose
• KDIGO: CKD Evaluation and Management guideline — creatinine and eGFR reporting

A note on this guide

This guide is general information about units and conversions. Conversion factors are rounded and are not a substitute for the laboratory’s own reporting. It is not medical advice, so please confirm what any result means for you with your doctor.