How common is your medical condition, really?

Dry socket (alveolar osteitis) occurs in approximately 2-5% of all tooth extractions. The rate rises significantly for wisdom tooth extractions, particularly lower (mandibular) third molars, where it reaches 25-30%. Dry socket happens when the blood clot that normally forms in the extraction socket is dislodged or dissolves before the wound heals. Risk factors include smoking, use of oral contraceptives, traumatic extractions, and poor post-operative oral hygiene. Symptoms typically appear 2-4 days after extraction. Source: Kolokythas et al. (2010), International Journal of Dentistry.

Some degree of iris colour variation is present in 15-20% of people, though most cases are subtle. Clearly visible central heterochromia occurs in roughly 1-2% of the population. This is different from complete heterochromia (two entirely different coloured eyes), which affects less than 1% of people. Central heterochromia is usually a benign genetic trait caused by uneven distribution of melanin in the iris during development. In rare cases, acquired heterochromia can signal conditions like Horner syndrome and should be evaluated by an ophthalmologist. Source: Sturm & Larsson (2009); American Academy of Ophthalmology.

When used on the first day of a missed period with first-morning urine, modern home pregnancy tests are 97-99% accurate (1-3% false negative rate). Testing before a missed period significantly reduces accuracy: tests taken even a few days early may only be 50-75% accurate because hCG levels may not yet be high enough to detect. Dilute urine can also cause false negatives. False positives are very rare and usually indicate a chemical pregnancy (very early pregnancy loss). If you get a negative result but your period does not arrive, retest in 2-3 days. Source: Cole et al. (2004), American Journal of Obstetrics and Gynecology.

Approximately 95% of 20-week anomaly scans show a completely normal result with no concerns. About 3-4% of scans identify "soft markers," which are minor findings that are usually benign but may prompt additional monitoring or follow-up scans. Significant structural anomalies are detected in approximately 2-3% of all scans. The 20-week scan is a screening tool, not a diagnostic test. Its sensitivity for detecting major anomalies varies by condition, ranging from about 50% for some heart defects to over 90% for conditions like anencephaly. Source: NHS Fetal Anomaly Screening Programme; Whitworth et al. (2015) Cochrane Review.

Miscarriage (pregnancy loss before 20 weeks) affects approximately 10-15% of known pregnancies. When accounting for losses before a pregnancy is detected (chemical pregnancies), the total rate may be as high as 25-30% of all conceptions. The vast majority of miscarriages (roughly 80%) occur in the first 12 weeks of pregnancy. After a heartbeat is confirmed on ultrasound at 8 weeks, the miscarriage risk drops significantly to about 2-4%. The most common cause is chromosomal abnormality in the embryo, which occurs randomly and is not caused by anything the parent did or did not do. Source: Tommy's National Centre for Miscarriage Research; ACOG.

Red-green colour blindness affects approximately 8% of men and 0.5% of women worldwide. The large sex difference exists because the most common forms are X-linked recessive traits: men have only one X chromosome, so a single affected copy causes the condition, while women need both X chromosomes to carry the variant. Total colour blindness (achromatopsia) is extremely rare, affecting approximately 1 in 30,000 people. Blue-yellow colour deficiency (tritanopia) affects about 1 in 10,000 and is equally common in men and women because the relevant gene is on chromosome 7, not the X chromosome. Source: National Eye Institute.

Ectopic pregnancy, where a fertilised egg implants outside the uterus, occurs in approximately 1-2% of all pregnancies. In the UK, this equates to roughly 11,000 cases per year. Risk factors include previous ectopic pregnancy, pelvic inflammatory disease, endometriosis, previous tubal surgery, and IVF (2-5% ectopic rate). Ectopic pregnancy is a medical emergency if the fallopian tube ruptures. Warning signs include sharp one-sided pelvic pain, vaginal bleeding, and shoulder tip pain. Early detection through ultrasound and hCG monitoring has significantly improved outcomes. Source: ACOG Practice Bulletin 193 (2018).

Yes, false positive drug tests occur more commonly than most people realise with initial immunoassay screening tests. Urine immunoassay tests for amphetamines can produce false positives from common over-the-counter medications like pseudoephedrine and certain antidepressants. Poppy seed consumption can trigger a positive for opiates. The false positive rate for initial screening tests ranges from approximately 5-10% for some drug classes, which is why positive screening results should always be confirmed with a more specific confirmatory test (typically GC-MS), which has a false positive rate of less than 0.1%. Source: SAMHSA guidelines; Mayo Clinic Proceedings.