Q. Our laboratory was cited for a deficiency because the manufacturer and methodology of our tumor marker assay was not available to clinicians. What is the reasoning behind this requirement?
A. November 2024—Tumor markers are measured to assess tumor burden and used for cancer diagnosis, prognosis, therapeutic monitoring, and detection of disease recurrence. Examples of tumor markers commonly measured in the routine clinical laboratory are prostate-specific antigen (PSA), human chorionic gonadotropin (hCG), α-fetoprotein (AFP), carcinoembryonic antigen (CEA), cancer antigen 125 (CA 125), cancer antigen 19-9 (CA 19-9), and prolactin. Measurements are typically obtained using automated immunoassays that employ antibodies directed against specific epitopes on tumor marker proteins.
Tumor marker measurements can vary widely as not all assay manufacturers use the same measurement procedures.1,2 Tumor-related proteins are highly heterogenous, with different molecular forms found in circulation due to proteolysis, post-translational modifications, and subunit expression. Lack of agreement among results from different assays can be attributed to use of reagent antibodies that recognize different epitopes or variations in reagent antibodies’ selectivity for specific molecular forms of proteins produced by the tumor.
Even if method-comparison studies show good overall agreement among assays, large discrepancies between patient samples can occur.3 For example, some beta hCG assays detect only intact hCG while others detect intact hCG plus molecular variants such as beta core fragment and free beta subunits. These differences in the antibody’s ability to recognize hCG molecular forms contribute to discrepancies in beta hCG results among assays.4
Lack of agreement among assays can also be attributed to differences in manufacturers’ calibration approaches. Laboratory tests are considered to be harmonized when results from different measurement procedures are equivalent.5 To achieve harmonization, manufacturers typically use commonly agreed upon reference materials for traceability of their calibrations. The reference materials must be commutable, meaning the results obtained for the materials must demonstrate the same bias relationship as patient samples when analyzed by different assays. Reference materials are not available for such tumor markers as CA 125, CA 19-9, and CA 15-3, resulting in a lack of harmonization for these assays.
Although reference materials are available for some tumor marker assays, such as free PSA and AFP, the materials are not commutable in all measurement procedures, or dilutions of the reference materials used to trace calibration are not commutable.6,7 Therefore, significant differences among measurement procedures persist.
A recent study evaluated agreement among commercial procedures commonly used for tumor marker measurement by routine clinical laboratories.8 The study found large differences in agreement among assays for CA 125, CA 15-3, and CA 19-9. For example, the relative difference between results from the lowest and highest assays was 99 percent for CA 125 and 549 percent for CA 19-9. This level of difference in tumor marker results among measurement procedures can have significant clinical impact, especially if results are interpreted using fixed clinical decision thresholds. For example, a CA 125 level greater than 35 U/mL has been associated with poor prognosis and increased prevalence of residual tumor after surgery and chemotherapy.9
The large variation among CA 125 measurement procedures could lead to differences in patient care. There can also be clinical impact when using results from different assays to monitor trends in patient results over time or trends in patients’ response to therapy. This might happen when a patient transfers care to another institution or when a laboratory implements a different manufacturer’s assay. In these types of cases, changes in patients’ results due to assay differences could be misinterpreted as changes in their tumor burden over time or as changes in their response to therapy.
Because total PSA (tPSA) is a critical tumor marker recommended in clinical guidelines for prostate cancer surveillance, considerable efforts have been undertaken by the laboratory community to harmonize tPSA measurement procedures. These efforts have improved overall agreement among tPSA assays and contrast efforts to harmonize measurement procedures for various other tumor markers. However, clinically actionable differences in measurements between various tPSA assays are possible, particularly in the lower range.3 Even small differences can be significant, depending on how the results are used in clinical decision-making (e.g. to evaluate tPSA doubling using two measurement procedures). Given the clinical impact of differences among manufacturers, the CAP recommends that laboratories establish a transition period when changing to a new assay, in which results from the old and new measurement procedures are reported.10 Reporting results from both assays allows providers to establish a new baseline for each patient with the new measurement procedure.
Due to potential adverse impacts on patient care resulting from large differences among methods, CAP-accredited laboratories are required to report the manufacturer and methodology used along with the tumor marker result or make the information available to clinicians in another way, such as by placing it in the laboratory test catalog. In addition, laboratories are required to provide a statement indicating that results from different manufacturers’ measurement procedures may not be comparable.
- van Rossum HH, Holdenrieder S, Ballieux BEPB, et al. Investigating the current harmonization status of tumor markers using global external quality assessment programs: a feasibility study. Clin Chem. 2024;70(4):669–679.
- Sturgeon C. Standardization of tumor markers—priorities identified through external quality assessment. Scand J Clin Lab Invest Suppl. 2016;76 (suppl 245):S94–S99.
- Rutledge AC, Pond GR, Hotte SJ, Kavsak PA. Assessing the necessity of including a crossover period with dual reporting when changing total prostate-specific antigen methods. Clin Biochem. 2014;47(10–11):897–900.
- Franks CE, Li J, Martinez M, et al. Utility of commercially available quantitative hCG immunoassays as tumor markers in trophoblastic and non-trophoblastic disease. Clin Chem. 2023;69(6):606–614.
- Tate JR, Johnson R, Barth J, Panteghini M. Harmonization of laboratory testing—current achievements and future strategies. Clin Chim Acta. 2014;432:4–7.
- Ferraro S, Bussetti M, Rizzardi S, Braga F, Panteghini M. Verification of harmonization of serum total and free prostate-specific antigen (PSA) measurements and implications for medical decisions. Clin Chem. 2021;67(3):543–553.
- Yue Y, Zhang S, Xu Z, Chen X, Wang Q. Commutability of reference materials for α-fetoprotein in human serum. Arch Pathol Lab Med. 2017;141(10):1421–1427.
- Kremser M, Weiss N, Kaufmann-Stoeck A, et al. Longitudinal evaluation of external quality assessment results for CA 15-3, CA 19-9, and CA 125. Front Mol Biosci. 2024;11:1401619.
- Markman M, Federico M, Liu PY, Hannigan E, Alberts D. Significance of early changes in the serum CA-125 antigen level on overall survival in advanced ovarian cancer. Gynecol Oncol. 2006;103(1):195–198.
- College of American Pathologists. CHM.29050 Tumor marker result reporting. In: Chemistry and toxicology checklist. Aug. 24, 2023.
Lorin M. Bachmann, PhD, DABCC
Professor of Pathology
Virginia Commonwealth University
Richmond, Va.
Member, CAP Accuracy-Based Programs Committee
Kathryn Brown, MD
Anatomic and Clinical Pathologist
Medical Laboratory Director
Hub Care Pathology Group and Merit Health
Jackson, Miss.
Member, CAP Accuracy-Based Programs Committee
Q. For patients who have a hematocrit level greater than 55 percent, is it okay to use a CBC (hematocrit) that was not collected at the same time as the citrate sample? For example, can we use a CBC collected within 24 hours for an inpatient and a CBC from a previous visit for an outpatient?
A. I am not aware of guidance that addresses the use of nonconcurrent hematocrit values to determine acceptability of a citrate specimen for coagulation testing. Clinical and Laboratory Standards Institute document H21-A5 addresses adjusting the citrate concentration for patients with high hematocrits since a hematocrit level above 55 percent leads to a relative excess of citrate in blue-top tubes (compared to the volume of plasma), which may cause prolonged clotting times.
Elevated hematocrit levels can occur in newborns and people who live at high altitudes or in those who are dehydrated or have severe burns, heart or lung disease, or myeloproliferative neoplasms such as polycythemia vera. The within-subject biological variation of hematocrit is three percent in healthy adults and more variable in patients who are acutely ill, due to their hydration status, treatment with intravenous fluids, or factors related to their underlying disease state. Therefore, the laboratory needs to determine the acceptable amount of time between receiving a hematocrit result and using it to determine whether a nonconcurrent coagulation specimen is acceptable based on its patient population. Laboratory policy may need to define procedures for different populations, such as relatively healthy outpatients versus acutely ill inpatients.
If a concurrent hematocrit is not available, the laboratory could perform a CBC on a blue-top tube and correct the results (multiply by 1.1) to account for the citrate diluting the specimen, with appropriate validation.
Clinical and Laboratory Standards Institute. H21-A5: Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays and Molecular Hemostasis Assays; Approved Guideline, 5th ed.; 2008.
Lahsaee SM, Ghaffaripour S, Hejr H. The effect of routine maintenance intravenous therapy on hemoglobin concentration and hematocrit during anesthesia in adults. Bull Emerg Trauma. 2013;1(3): 102–107.
Thirup P. Haematocrit: within-subject and seasonal variation. Sports Med. 2003;33(3):231–243.
Kristi J. Smock, MD
Professor of Pathology
University of Utah School of Medicine
Hematopathology Medical Director
Hemostasis/Thrombosis Laboratory
ARUP Laboratories
Salt Lake City, Utah
Vice Chair, CAP Hemostasis and Thrombosis Committee