Diagnostic Tests

What Physicians Need to Know

FM/a Blood Test for Diagnosis of Fibromyalgia

 

Am Fam Physician. 2021 May 1;103(9):566-567.

The FM/a Test is a blood test used for the diagnosis of fibromyalgia. It is available for use in patients of any age who have at least four of the typical symptoms of fibromyalgia.1

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TestIndicationPopulation and frequencyCost*

FM/a Test

Diagnostic test for fibromyalgia

Patients with an uncertain diagnosis who have at least four of the typical symptoms of fibromyalgia† One-time test

$1,080


*—Cost without insurance according to the manufacturer (Dr. Bruce Gillis, Epic-Genetics, email, January 24, 2021).

†—Common fibromyalgia symptoms are chronic fatigue, many painful or tender areas, mental/brain fogginess, poor sleep, trouble concentrating, frequent headaches, joint aches, leg cramps, restless legs when sleeping, anxiety/nervousness, feeling depressed, numbness or tingling.

Information from reference 1.

TestIndicationPopulation and frequencyCost*

FM/a Test

Diagnostic test for fibromyalgia

Patients with an uncertain diagnosis who have at least four of the typical symptoms of fibromyalgia† One-time test

$1,080


*—Cost without insurance according to the manufacturer (Dr. Bruce Gillis, Epic-Genetics, email, January 24, 2021).

†—Common fibromyalgia symptoms are chronic fatigue, many painful or tender areas, mental/brain fogginess, poor sleep, trouble concentrating, frequent headaches, joint aches, leg cramps, restless legs when sleeping, anxiety/nervousness, feeling depressed, numbness or tingling.

Information from reference 1.

Accuracy

Fibromyalgia has historically been diagnosed using the American College of Rheumatology clinical criteria (Table 1).2 The FM/a Test is a cytokine assay of in vitro stimulated peripheral blood mononuclear cells. Production of cytokines by stimulated immune cells in patients with fibromyalgia has been shown to be significantly different from that of healthy control patients.3,4 Based on the concentrations of four cytokines, a cytokine/chemokine composite score, calculated as 1 / (1 + e−x) * 100, on a scale of 0 to 100 was developed. A score greater than 50 is considered positive for fibromyalgia.4

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TABLE 1.

2016 American College of Rheumatology Fibromyalgia Diagnostic Criteria

Generalized pain, defined as pain in at least four of five regions, is present.

Symptoms have been present at a similar level for at least three months.

Widespread pain index score is ≥ 7 and symptom severity scale score is ≥ 5, or widespread pain index score is 4 to 6 and symptom severity score is ≥ 9.

A diagnosis of fibromyalgia is valid irrespective of other diagnoses. A diagnosis of fibromyalgia does not exclude the presence of other clinically important illnesses.


Information from reference 2.

TABLE 1.

2016 American College of Rheumatology Fibromyalgia Diagnostic Criteria

Generalized pain, defined as pain in at least four of five regions, is present.

Symptoms have been present at a similar level for at least three months.

Widespread pain index score is ≥ 7 and symptom severity scale score is ≥ 5, or widespread pain index score is 4 to 6 and symptom severity score is ≥ 9.

A diagnosis of fibromyalgia is valid irrespective of other diagnoses. A diagnosis of fibromyalgia does not exclude the presence of other clinically important illnesses.


Information from reference 2.

A study of 160 patients with fibromyalgia based on the American College of Rheumatology criteria and 119 healthy control patients found that a positive FM/a Test result has a sensitivity of 93% and a specificity of 89% (Table 2).4 The positive likelihood ratio was 8.5, and the negative likelihood ratio was 0.08. However, this type of study design, which uses a control group of healthy patients, overestimates accuracy. In the same study, when using a more appropriate comparison group of patients with known rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE) who did not have co-occurring fibromyalgia, the specificity was only 70%, with a positive likelihood ratio of 3.1 and a negative likelihood ratio of 0.1. The most appropriate study design would enroll patients with clinically suspected fibromyalgia, but this type of study has not been performed.

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TABLE 2.

Performance Characteristics of the FM/a Test

DiagnosisSensitivity (%)Specificity (%)LR+LR−

Fibromyalgia vs. healthy controls

93

89

8.5

0.08

Fibromyalgia vs. rheumatoid arthritis or systemic lupus erythematosus

93

70

3.1

0.1


LR− = negative likelihood ratio; LR+ = positive likelihood ratio

Information from reference 4.

TABLE 2.

Performance Characteristics of the FM/a Test

DiagnosisSensitivity (%)Specificity (%)LR+LR−

Fibromyalgia vs. healthy controls

93

89

8.5

0.08

Fibromyalgia vs. rheumatoid arthritis or systemic lupus erythematosus

93

70

3.1

0.1


LR− = negative likelihood

Address correspondence to Anne Mounsey, MD, at anne_mounsey@med.unc.edu. Reprints are not available from the authors.

Author disclosure: No relevant financial affiliations.

References

show all references

1. EpicGenetics. FM/a Test. Accessed January 23, 2021. http://www.fmtest.com...

2. Wolfe F, Clauw DJ, Fitzcharles M-A, et al. 2016 revisions to the 2010/2011 fibromyalgia diagnostic criteria. Semin Arthritis Rheum. 2016;46(3):319–329.

3. Behm FG, Gavin IM, Karpenko O, et al. Unique immunologic patterns in fibromyalgia. BMC Clin Pathol. 2012;12:25.

4. Wallace DJ, Gavin IM, Karpenko O, et al. Cytokine and chemokine profiles in fibromyalgia, rheumatoid arthritis and systemic lupus erythematosus: a potentially useful tool in differential diagnosis. Rheumatol Int. 2015;35(6):991–996.

5. Srinivasan S, Maloney E, Wright B, et al. The problematic nature of fibromyalgia diagnosis in the community. ACR Open Rheumatol. 2019;1(1):43–51.

6. Zhao SS, Duffield SJ, Goodson NJ. The prevalence and impact of comorbid fibromyalgia in inflammatory arthritis. Best Pract Res Clin Rheumatol. 2019;33(3):101423.

7. Middleton GD, McFarlin JE, Lipsky PE. The prevalence and clinical impact of fibromyalgia in systemic lupus erythematosus. Arthritis Rheum. 1994;37(8):1181–1188.

8. Annemans L, Wessely S, Spaepen E, et al. Health economic consequences related to the diagnosis of fibromyalgia syndrome. Arthritis Rheum. 2008;58(3):895–902.

This series is coordinated by Kenny Lin, MD, MPH, deputy editor.

A collection of Diagnostic Tests published in AFP is available at https://www.aafp.org/afp/diagnostic.

 

 

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