Table 1.
Baseline characteristics of the study sample of patients by porphyria status before and after matching, 2011–2014
| Patient characteristicsa | Porphyria (n = 2788) | No porphyria (n = 623,816) | Standardized difference before matchingb | Matchedc no porphyria controls (n = 2788) | Standardized difference after matchingb |
|---|---|---|---|---|---|
| Age, mean (SD) | 48.28 (11.40) | 48.82 (10.77) | 0.0462 | 48.38 (11.18) | 0.0088 |
| Age group, n (%) | 0.0663 | N/A | |||
| 18–34 years | 388 (13.92) | 73,854 (11.84) | 388 (13.92) | ||
| 35–44 years | 487 (17.47) | 117,040 (18.76) | 487 (17.47) | ||
| 45–54 years | 886 (31.78) | 201,835 (32.46) | 886 (31.78) | ||
| 55 + years | 1027 (36.84) | 231,087 (37.04) | 1027 (36.84) | ||
| Gender, n (%) | 0.0566 | N/A | |||
| Male | 1251 (44.87) | 297,522 (47.69) | 1251 (44.87) | ||
| Female | 1537 (55.13) | 326,294 (52.31) | 1537 (55.13) | ||
| US region of residence, n (%) | 0.0474 | 0.1125 | |||
| Northeast | 569 (20.41) | 138,754 (22.24) | 672 (24.10) | ||
| North Central | 503 (18.04) | 111,794 (17.92) | 485 (17.40) | ||
| South | 1122 (40.24) | 244,103 (39.13) | 1134 (40.67) | ||
| West | 539 (19.33) | 118,254 (18.96) | 450 (16.14) | ||
| Unknown | 55 (1.97) | 10,911 (1.75) | 47 (1.69) | ||
| Type of health insurance, n (%) | 0.0522 | 0.1597 | |||
| Preferred provider organization | 1754 (62.91) | 381,649 (61.18) | 1540 (55.24) | ||
| Health maintenance organization | 314 (11.26) | 79,954 (12.82) | 394 (14.13) | ||
| Comprehensive | 85 (3.05) | 17,670 (2.83) | 110 (3.95) | ||
| Point of service | 219 (7.86) | 50,270 (8.06) | 271 (9.72) | ||
| Other | 416 (14.92) | 94,273 (15.11) | 473 (16.97) | ||
| Comorbidity profiled | |||||
| Charlson comorbidity index, mean (SD) | 1.10 (1.77) | 1.45 (2.09) | 0.1821 | 1.18 (1.81) | 0.0467 |
| Charlson comorbidity index, n (%) | 0.1967 | 0.0599 | |||
| 0 | 1440 (51.65) | 271,497 (43.52) | 1379 (49.46) | ||
| 1 | 661 (23.71) | 153,450 (24.60) | 655 (23.49) | ||
| 2 | 283 (10.15) | 73,971 (11.86) | 317 (11.37) | ||
| 3 | 193 (6.92) | 50,345 (8.07) | 199 (7.14) | ||
| 4 + | 211 (7.57) | 74,553 (11.95) | 238 (8.54) | ||
| Alcohol abuse or dependence, n (%) | 22 (0.79) | 11,311 (1.81) | 0.0905 | 27 (0.97) | 0.0192 |
| Liver transplant, n (%) | 4 (0.14) | 5239 (0.84) | 0.0997 | 4 (0.14) | N/A |
| Hepatocellular carcinoma, n (%) | 5 (0.18) | 4846 (0.78) | 0.0867 | 4 (0.14) | 0.0894 |
| Decompensated cirrhosis, n (%) | 54 (1.94) | 77,927 (12.49) | 0.4167 | 54 (1.94) | N/A |
| Compensated cirrhosis, n (%) | 34 (1.22) | 23,542 (3.77) | 0.1643 | 33 (1.18) | 0.0329 |
| Alcoholic fatty liver, n (%) | 9 (0.32) | 11,061 (1.77) | 0.1428 | 9 (0.32) | N/A |
| Hepatitis C virus, n (%) | 116 (4.16) | 60,019 (9.62) | 0.2168 | 147 (5.27) | 0.5247 |
| Hepatitis B virus, n (%) | 7 (0.25) | 18,464 (2.96) | 0.2168 | 7 (0.25) | N/A |
| Hemochromatosis, n (%) | 51 (1.83) | 42,886 (6.87) | 0.2492 | 52 (1.87) | 0.0027 |
| Non-alcoholic fatty liver, n (%) | 128 (4.59) | 366,071 (58.68) | 1.4298 | 128 (4.59) | N/A |
| Other chronic liver diseasese, n (%) | 5 (0.18) | 11,294 (1.81) | 0.1649 | 5 (0.18) | N/A |
N/A exactly matched or identical number of cases and controls, SD standard deviation
aAll demographics data were obtained on index date (first diagnosis date of porphyria for cases and a randomly selected date from all claim records for controls) for chronic liver disease adult participants with continuous enrollment during the 12 months prior and the 12 months following index date
bDifference in means or proportions divided by the standard error. Smaller values indicate better balance between cases and controls
cPorphyria cases and porphyria-free controls with chronic liver disease were matched 1:1 using propensity score. The logistic regression model used to estimate the propensity scores included age group, region of residence, gender, type of health insurance, Charlson comorbidity index, alcohol abuse or dependence liver transplant, hepatocellular carcinoma, decompensated cirrhosis, compensated cirrhosis, alcoholic fatty liver, hepatitis C virus, hepatitis B virus, hemochromatosis, non-alcoholic fatty liver, and other chronic liver disease. In turn, cases and controls were exactly matched on age group and gender
dWas estimated during the 12 months prior to the index date
eIncluded patients with autoimmune hepatitis, hepatitis E virus, primary biliary cirrhosis, or primary sclerosing cholangitis