Trusting numbers: uncertainty and the pathology laboratory

Reference Intervals for Platelet Counts in the Elderly: Results from the Prospective SENIORLAB Study

Currently, age- and sex-independent reference limits (RLs) are frequently used to interpret platelet counts in seniors. We aimed to define and validate reference intervals (RIs) for platelet counts within the framework of the prospective SENIORLAB study. Subjectively healthy Swiss individuals aged 60 years and older were prospectively included and followed for morbidity and mortality. Participants who had circumstances known to affect platelet counts were excluded. The obtained RIs were validated with indirect statistical methods. Frequencies of abnormal platelet counts in a population-based setting, including 41.5% of the entire age-specific population of the Principality of Liechtenstein, were compared by using age- and sex-independent RIs and the RLs obtained in the present study. For males (n = 542), 95% RIs for platelet counts were defined as follows: 150–300 × 10⁹/L (60–69 years); 130–300 × 10⁹/L (70–79 years); and 120–300 × 10⁹/L (80 years and above). For females (n = 661), the consolidated age-independent 95% RI was 165–355 × 10⁹/L. These RI values were validated by indirect RI determination of 51,687 (30,392 female/21,295 male) patients of the same age. Age- and sex-independent RIs exhibited imbalanced frequencies of abnormal platelet counts between the two sexes, which were corrected by introducing age- and sex-specific RLs. In conclusion, females have higher platelet counts than males. Whereas the upper RL for males remains constant, the lower RL decreases with age. We propose to abandon the practice of employing sex- and age-independent RL for platelet counts in the elderly.

Untreated hypertension among Australian adults: the 1999-2000 Australian Diabetes, Obesity and Lifestyle Study (AusDiab)

OBJECTIVE

To measure the prevalence of untreated hypertension in Australian adults, and examine the associations with clinical and lifestyle factors.

DESIGN

AusDiab, a cross-sectional survey conducted between May 1999 and December 2000, involved participants from 42 randomly selected census districts throughout Australia.

PARTICIPANTS

Of 20 347 eligible people aged >or= 25 years who completed a household interview, 11 247 attended a physical examination (response rate, 55%).

MAIN OUTCOME MEASURES

The prevalence of hypertension (blood pressure >or= 140/90 mmHg or self-reported use of antihypertensive drugs) and its treatment; associations of clinical and lifestyle factors with the treatment of hypertension; and adequacy of treatment for primary and secondary prevention of cardiovascular disease.

RESULTS

The prevalence of hypertension was 28.6 per 100 (95% CI, 25.0-32.3), and the prevalence of untreated hypertension was 15.2 per 100 (95% CI, 13.2-17.2). Of those with untreated hypertension, 80.8% (95% CI, 74.7%-85.0%) had had a blood pressure check within the preceding 12 months. At least one modifiable lifestyle factor was present in 71.7% (95% CI, 68.5%-74.8%) of participants with untreated hypertension. Although lower risk clinical characteristics of younger age and lack of hyperlipidaemia were independently associated with untreated hypertension, 53.5% warranted treatment based on current cardiovascular disease prevention guidelines and multivariable absolute risk assessment.

CONCLUSIONS

Considerable scope remains for reducing the burden of cardiovascular disease through lifestyle modification and rational treatment of hypertension.