CA 72-4 Unit Converter
CA 72-4 Unit Converter
U/mL and kU/L are the same number for CA 72-4. The interpretation is the work: a gastric and mucinous ovarian marker with a cut-off that belongs to the assay, and a famous false positive from colchicine.
CA 72-4 converter
U/mL ⇄ kU/LCA 72-4 3.1 U/mL
Formula and conversion factors
U/L = U/mL × 1000
- U/mL = kU/L
- a unit per millilitre is a kilounit per litre, so the two are the same number and nothing is calculated between them
- arbitrary units
- the unit is defined by each assay's own calibrator against the CC49 and B72.3 antibodies, not by a mass, so there is no molar conversion and never can be
- assay dependence
- the upper limit is the manufacturer's, not a universal one; a patient followed on CA 72-4 must stay on a single platform for serial results to mean anything
Worked example
CA 72-4 3.1 U/mL
3.1 U/mL = 3.1 kU/L — the two units are identical
3.1 × 1000 = 3,100 U/L
No band is shown: the cut-off printed on your own report is the one that applies
The three units
| Unit | Relationship | Example |
|---|---|---|
| U/mL | The usual reporting convention | 3.1 |
| kU/L | Identical to U/mL | 3.1 |
| U/L | U/mL × 1000 | 3,100 |
Reading a CA 72-4
| Question | Answer |
|---|---|
| What is it used for? | Gastric cancer and mucinous ovarian cancer, almost always alongside CEA and CA 19-9 rather than alone |
| How sensitive is it? | Less sensitive on its own than CEA or CA 19-9 in gastric cancer, but it detects some tumours those two miss, so a combination performs better than any single marker |
| Is it a screening test? | No. It is not recommended for detecting cancer in people without symptoms |
| What raises it without cancer? | Benign gastrointestinal, pancreatic, hepatic, ovarian and rheumatic disease; gout flares in particular |
| Which drug is notorious for it? | Colchicine. Repeated case series describe a marked, isolated CA 72-4 rise that resolves when the drug is stopped, with all other markers normal |
| What is the cut-off? | Whatever your laboratory prints. It is the manufacturer’s figure for one analyser, and figures differ between platforms |
A marker that is almost never read alone
CA 72-4 is reported in U/mL or in kU/L, and those are the same number, because a unit per millilitre is a kilounit per litre. Only U/L is different, being a thousand times larger. There is no molar column on this page and there cannot be one: CA 72-4 measures the TAG-72 mucin epitope in arbitrary units defined by each assay’s own calibrator, so no molecular mass applies. All the difficulty is in the interpretation, not the arithmetic.
Clinically the marker belongs to gastric cancer and to mucinous ovarian cancer, where CA 125 often performs poorly. On its own it is less sensitive than either CEA or CA 19-9 in gastric cancer, which is why it is rarely measured in isolation. Its value is additive: it picks up a proportion of tumours the other two miss, so a panel detects more than any single marker does. It is not a screening test and is not recommended for finding cancer in people without symptoms.
The list of benign causes is broad — inflammatory and benign disease of the stomach, pancreas, liver and ovary all raise it — but one deserves its own sentence. Colchicine causes a striking, isolated rise in CA 72-4, documented in repeated case reports and series, with CEA, CA 19-9 and the rest of the panel entirely normal, and the level falls once the drug is withdrawn. Serum CA 72-4 is also raised during acute gout flares, which is the same population. A raised CA 72-4 in a patient on colchicine should prompt that question before it prompts a scan.
This page prints no reference band deliberately. Every published cut-off for CA 72-4 is a manufacturer’s figure for one analyser, and they are not interchangeable, so the number on your own report is the only one that applies to your result. The same constraint governs monitoring: a trend is only a trend if every sample was run on the same assay. Tumour markers are interpreted in context by a clinician who has the imaging, the drug history and the rest of the panel. No single value diagnoses anything.
Frequently asked questions
Is U/mL the same as kU/L for CA 72-4?
Yes. A unit per millilitre is a kilounit per litre, so the two are the same number and nothing needs converting. Only U/L differs: it is a thousand times larger, so 3.1 U/mL is 3.1 kU/L and 3,100 U/L. There is no molar unit for CA 72-4.
Why is no normal range shown on this page?
Because there is no universal one. Every published CA 72-4 cut-off is the figure the manufacturer set for their own analyser, and those figures differ between platforms. Printing one as though it applied everywhere would mislead more readers than it helped, so the page defers to the interval on your report.
Can colchicine raise CA 72-4?
Yes, and it is the best-known false positive for this marker. Case reports and series describe a marked isolated rise in CA 72-4 in patients taking colchicine, with CEA, CA 19-9 and other markers normal, which settles after the drug is stopped. It is worth telling the requesting clinician if you take it.
What is CA 72-4 used for?
Mainly gastric cancer and mucinous ovarian cancer, and almost always as part of a panel with CEA and CA 19-9. It is less sensitive than either of those alone in gastric cancer but detects some tumours they miss, so the combination performs better than any of them individually.
Can CA 72-4 be used to screen for stomach cancer?
No. It is not recommended for detecting cancer in people without symptoms: too many benign conditions raise it and too many early cancers do not. Its established roles are assessing prognosis and following response or recurrence in disease that is already diagnosed.
Related calculators
References
- Zhao B, Zhang M, Xie J, et al. An abnormal elevation of serum CA72-4 due to taking colchicine. Clin Chem Lab Med. 2017;56(1):e13–e15.
- Bai X, Sun M, He Y, et al. Serum CA72-4 is specifically elevated in gout patients and predicts flares. Rheumatology (Oxford). 2020;59(10):2872–2880.
- Sturgeon CM, Duffy MJ, Hofmann BR, et al. National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines for use of tumor markers in liver, bladder, cervical, and gastric cancers. Clin Chem. 2010;56(6):e1–e48.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.