Table 2.
Summary regression results. Dependent variable: log of the medical expenditures of test for 86580 (TST) and 86480 (QFT-GIT). N = 628,595.
| Independent variables | Coefficient (β)† [95% CI] | Transformed coefficient (%) [95% CI]‡ |
|---|---|---|
| Age of patient | 0.0048 [0.0045 to 0.0051]∗∗∗ | 0.48 [0.45 to 0.51] |
| Age-squared variable | −0.0000558 [−0.0000603 to −0.0000513]∗∗∗ | −0.0056 [−0.0060 to −0.0051] |
| Quantity of services | 0.16263 [0.1577 to 0.1676]∗∗∗ | 16.26 [15.77 to 16.76] |
| Gender | ||
| Male | Referent | Referent |
| Female | −0.0032 [−0.0059 to −0.0006]∗∗ | −0.32 [−0.59 to −0.06] |
| Data supplier | ||
| Employer | Referent | Referent |
| Health plan | −0.0059 [−0.0091 to −0.0026]∗∗∗ | −0.59 [−0.91 to −0.26] |
| Drug coverage? | ||
| No | Referent | Referent |
| Yes | −0.005 [−0.0086 to −0.0014]∗∗∗ | −0.5 [−0.86 to −0.14] |
| Region | ||
| South | Referent | Referent |
| Northeast | 0.1147 [0.1111 to 0.1183]∗∗∗ | 12.15 [11.75 to 12.56] |
| North Central | 0.2134 [0.2092 to 0.2176]∗∗∗ | 23.79 [23.27 to 24.31] |
| West | 0.2795 [0.2757 to 0.2833]∗∗∗ | 32.25 [31.75 to 32.75] |
| Unknown | 0.1743 [0.1653 to 0.1833]∗∗∗ | 19.04 [17.97 to 20.12] |
| Health plan type | ||
| Comprehensive | Referent | Referent |
| Exclusive provider organization (EPO) | −0.0692 [−0.083 to −0.0553]∗∗∗ | −6.69 [−7.96 to −5.38] |
| Health maintenance organization (HMO) | −0.007 [−0.0195 to 0.0056] | −0.7 [−1.93 to 0.56] |
| Point of service (POS) | −0.0478 [−0.0609 to −0.0348]∗∗∗ | −4.67 [−5.91 to −3.42] |
| Preferred provider organization (PPO) | −0.0306 [−0.0428 to −0.0183]∗∗∗ | −3.01 [−4.19 to −1.81] |
| POS with capitation | −0.1314 [−0.1502 to −0.1127]∗∗∗ | −12.31 [−13.95 to −10.66] |
| Consumer driven health plan (CDHP) | −0.0795 [−0.0928 to −0.0662]∗∗∗ | −7.64 [−8.86 to −6.41] |
| High deductible health plan (HDHP) | −0.0996 [−0.1129 to −0.0863]∗∗∗ | −9.48 [−10.68 to −8.27] |
| Expenditures (difference) | ||
| 86580 (TST) | Referent | Referent |
| 86480 (QFT-GIT) | 2.0627 [2.0587 to 2.0666]∗∗∗ | 686.72 [683.58 to 689.79] |
Significance levels: ∗∗∗p < 0.01; ∗∗p < 0.05. †The t-values associated with the coefficients were derived from bootstrap-generated standard errors with 50 replications. ‡Because the dependent variables in the regression analyses were the natural log of dependent variable (medical expenditures), the coefficients were transformed as coefficient (β)∗100 and interpreted as the relative change (in percentage) per unit change in the independent variable (IV) for the continuous IVs and as (eβ − 1)∗100 and interpreted as the relative difference (in percentage) in the estimated medical expenditures when compared with the referent (or omitted) category [13]. The brand names for the respective IGRA testing method CPT codes (i.e., QuantiFERON-TB Gold In-Tube [QFT-GIT] for 86480 and T-SPOT.TB [T-Spot] for 86481) were used because they were the only IGRA tests approved by the Food and Drug Administration (FDA) as of 2013 [7].