Is Labcorp or Quest more accurate?

Both are large accredited laboratories. Differences in their reference ranges reflect methods, populations and chosen cut-offs, not accuracy. What matters most is comparing your result with the range printed by the lab that ran it.

Can I compare a Labcorp result with a Quest result?

With care. Small differences may simply reflect different methods. For tracking a value over time, using the same laboratory is more reliable.

Why is my result flagged at one lab but not the other?

Because the flag is set by each lab’s own reference range. A vitamin D of 25 ng/mL is inside Labcorp’s range (20–100) but below Quest’s (30–100). A man’s ferritin of 35 ng/mL is inside Labcorp’s adult range (30–400) but below Quest’s range for men aged 19–59 (38–380).

Testing · Labs compared

Labcorp vs. Quest: why your reference ranges differ

Short answer

The two largest US labs print different “normal” ranges for the same test because they use different analyzers, different reagents, different reference populations and, for some tests, different cut-offs. Neither range is wrong. The rule that follows: always read a result against the range on your own report, and use the same lab when you’re tracking a number over time.

Side by side

* Labcorp’s online test menu doesn’t list these ranges. They come from Labcorp’s published sample report for its iron and TIBC test (an adult male example), so they may not reflect sex- or age-specific ranges. † Quest’s standard iron and TIBC test reports serum iron, TIBC and saturation, but not UIBC. Quest’s ferritin and iron ranges are split by age; the table shows its adult bands.

Adult reference ranges as published by each lab · checked Sep 20, 2026
Test	Unit	Labcorp	Quest
Ferritin, women	ng/mL	15–150	16–154 (19–40 y) 16–232 (41–60 y) 16–288 (over 60)
Ferritin, men	ng/mL	30–400	38–380 (19–59 y) 24–380 (over 59)
Serum iron, women	µg/dL	27–159 (18–60 y) 27–139 (over 60)	40–190 (20–49 y) 45–160 (50+)
Serum iron, men	µg/dL	38–169	50–195 (20–29 y) 50–180 (30+)
TIBC	µg/dL	250–450*	250–450 (women) 250–425 (men)
UIBC	µg/dL	111–343*	Not reported†
Transferrin saturation	%	15–55*	16–45 (women) 20–48 (men)
25-OH vitamin D	ng/mL	20.0–100.0	30–100
Vitamin B12	pg/mL	232–1245	200–1100

Why the same test gets different ranges

Different methods. Ferritin and B12 are measured by immunoassays from several manufacturers, and results are not perfectly interchangeable between them.
Different reference populations. Each lab sets or adopts its range from a group of people it considers healthy. Different groups give different ranges.
Different conventions. Quest splits many adult ranges into age bands; Labcorp often gives a single adult range. Some ranges are sex-specific at one lab and not the other.

Vitamin D: same standard, different cut-off

Many vitamin D tests are certified by a CDC standardization program, so the measurement itself tends to agree more closely between labs than for other tests. The ranges still differ: Labcorp’s lower limit is 20 ng/mL and Quest’s is 30 ng/mL. That gap is about interpretation, not measurement. The National Academies consider 20 ng/mL or more sufficient for most people, but experts haven’t settled on a single deficiency cut-off, and the labs have chosen differently.

What this means for your results

Use the range on your report, not one you found online — including on this site.
Stay with one lab for repeat tests. A change from 28 to 35 means more if both were measured the same way.
Remember ranges aren’t thresholds. A result can be inside the printed range and still below a clinical cut-off — see what counts as a good ferritin level.

Common questions

Is Labcorp or Quest more accurate?: Both are large accredited laboratories. Differences in their reference ranges reflect methods, populations and chosen cut-offs, not accuracy. What matters most is comparing your result with the range printed by the lab that ran it.
Can I compare a Labcorp result with a Quest result?: With care. Small differences may simply reflect different methods. For tracking a value over time, using the same laboratory is more reliable.
Why is my result flagged at one lab but not the other?: Because the flag is set by each lab’s own reference range. A vitamin D of 25 ng/mL is inside Labcorp’s range (20–100) but below Quest’s (30–100). A man’s ferritin of 35 ng/mL is inside Labcorp’s adult range (30–400) but below Quest’s range for men aged 19–59 (38–380).