Normal Lab Values for Nurses: Units and Reference Ranges

A reference interval is the range of results a laboratory expects for a healthy group, and it is not the same everywhere. The number depends on the lab, the test method, and often the person’s age and sex, and the unit matters as much as the number. Use the range printed on your lab’s report, and treat any table, including the one below, as a typical adult guide.

The values

Each row below is traced to the linked MedlinePlus page. These are typical adult ranges; use your lab’s reference range.

Several of these pages say normal ranges may vary slightly among laboratories. The BUN page says normal values may vary among different labs, and the creatinine page adds that some labs use different measurement units. The hemoglobin and glucose pages make the same point.

Notice that for sodium, potassium and chloride the number is the same in mEq/L and mmol/L, because each ion carries a charge of one. Glucose, creatinine and hemoglobin change numbers when the unit changes.

Using it in NurseTools

The Lab Values tool is in clinical review and is not available yet. The app is coming soon to the App Store, and nothing is downloadable now. The app shows a release-gates timeline: source and rights audit, clinical editorial review, independent testing, and regulatory and App Store review. There is also a “Notify me when available” switch. Nothing unlocks a tool that has not passed review. Only BMI and MAP are planned for launch.

The planned design is to show lab values with their units, because reference intervals vary by lab, and to show each reference card’s sources, version and review date. The app is designed to need no account, never ask for patient data, and work offline.

Worked example

This is a made-up practice example, not a patient. Suppose a practice report from a lab that uses SI units shows a fasting glucose of 5.8 mmol/L. You want to compare it with a conventional mg/dL reference.

1. The glucose factor is 18. To go from mmol/L to mg/dL, multiply by 18.
2. 5.8 x 18 = 104.4 mg/dL.
3. Round to 104 mg/dL.
4. Compare with the MedlinePlus fasting range of 70 to 99 mg/dL. The converted value of 104 is above that typical range.

To go the other way, divide by 18. For example, 99 mg/dL divided by 18 is 5.5 mmol/L, which matches the upper end of the SI range on the MedlinePlus blood sugar page. The page lists 70 mg/dL as 3.9 mmol/L, and 70 / 18 is about 3.9.

What a value outside the range means for a person is a provider’s call, and your facility’s policy decides what you do next.

Limits and common pitfalls

• A single table cannot replace your lab’s range. MedlinePlus says normal ranges may vary slightly among laboratories.
• Sex matters for some tests. The creatinine and hemoglobin pages list separate male and female ranges.
• Check the unit before the number. Mixing mg/dL with mmol/L is an easy error, and the 18 factor applies to glucose only, not to other tests.
• Random glucose is judged differently from fasting glucose. The blood sugar page lists a random value of usually 125 mg/dL or lower, depending on when the person last ate.
• Units can also differ within one lab report. The creatinine page lists both mg/dL and µmol/L, so read the unit printed beside the result, not only the number.
• Rounding can shift a result across a cutoff, so keep a decimal place until the final step.