Plasma interleukin-6 and C-reactive protein levels in reactive versus clonal thrombocytosis.
OBJECTIVE
Evaluate the discriminatory value of plasma interleukin-6 or C-reactive protein levels in clonal thrombocytosis compared with those in reactive thrombocytosis.


METHODS
A comparative analysis of quantitatively measured laboratory values in a prospectively studied group of consecutive patients. The setting was a tertiary referral center consisting of two hospitals and an outpatient clinic. Plasma interleukin-6 and C-reactive protein levels were measured in 91 consecutive patients with thrombocytosis (platelet count > or = 600 x 10(9)/L). The cause of thrombocytosis was determined by reviewing the medical histories and follow-up data without knowledge of the corresponding laboratory values. Sixty-four patients had reactive thrombocytosis, 20 had clonal thrombocytosis, and 7 had clonal thrombocytosis plus reactive thrombocytosis. Plasma interleukin-6 was measured by an enzyme-linked immunosorbent assay, and C-reactive protein was measured with rate immunonephelometry.


RESULTS
Interleukin-6 levels were undetectable in all the patients with clonal thrombocytosis, whereas they were increased in 60% of the patients with reactive thrombocytosis or clonal thrombocytosis plus reactive thrombocytosis. There was a correlation between interleukin-6 and C-reactive protein levels (r = .6), and the median and range values of both levels differed significantly between the clonal thrombocytosis group and the other two groups (P < 0.0001). In 81% of the patients with reactive thrombocytosis, levels of either interleukin-6 or C-reactive protein were elevated. There was no correlation between interleukin-6 and C-reactive protein levels and the platelet count.


CONCLUSIONS
An elevated interleukin-6 level is rare in uncomplicated clonal thrombocytosis and suggests reactive thrombocytosis. However, an isolated normal value has little discriminatory value. Measurement of C-reactive protein level may be used as a less expensive surrogate for measurement of interleukin-6. Repeatedly low levels of both interleukin-6 and C-reactive protein are most consistent with clonal thrombocytosis.
Tefferi
A
A
Division of Hematology and Internal Medicine, Mayo Clinic, Rochester, Minnesota 55905.
Ho
T C
TC
Ahmann
G J
GJ
Katzmann
J A
JA
Greipp
P R
PR
D000368:Aged; D002097:C-Reactive Protein / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007118:Immunoassay; D015850:Interleukin-6 / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009391:Nephelometry and Turbidimetry; D010976:Platelet Count; D011446:Prospective Studies; D013922:Thrombocytosis / Q000097:blood* / Q000209:etiology / Q000276:immunology
D015850:Interleukin-6; D002097:C-Reactive Protein