Tuberculin skin test: estimation of positive and negative predictive values from routine data.

OBJECTIVE: To estimate, using routinely available data, the predictive values of tuberculin testing with 2TU RT23 for detection of latent tuberculosis infection (LTBI) in the Dutch population as a basis for recommendations on cut-off values at various levels of infection prevalence. DESIGN: Smoothed distributions of TST reactions among 312 tuberculosis patients and 2848 healthy non-BCG-vaccinated persons were used to estimate the sensitivity and specificity at various cut-off values. RESULTS: Sensitivity was 98.9% at 5 mm, 95.4% at 10 mm and 79.8% at 15 mm cut-off. Specificity with the corresponding cut-offs was 95.3%, 96.3% and 97.1% before and 98.0%, 98.8% and 99.6% after adjustment for presumed LTBI. At 10 mm, the positive predictive value (PPV) was > 75% if the infection prevalence in the tested population was at least 10%, but strongly declined with lower prevalences. For lower prevalences a cut-off of 15 mm was proposed, as this results in a higher PPV without greatly affecting the negative predictive value. CONCLUSION: Estimation of the predictive values of the TST from routine data can be useful for establishing cut-off values for detection of LTBI in different populations with different tuberculin preparations.

Urinary excretion rates of calcium and magnesium in normal and complicated pregnancies.

In this cross-sectional study calcium and magnesium metabolism was investigated in normal pregnancies (n = 34) and pregnancies complicated by either fetal growth retardation of hypertension with or without fetal growth retardation (SGA newborns) (n = 30). Special attention has been given to the renal excretion rates of calcium and magnesium and their relationship to creatinine and sodium clearances. No differences were noted in the third trimester of pregnancy between the normal and complicated pregnancies in calcium or magnesium metabolism except for an increased serum magnesium in the SGA group. Comparing the post-partum period to normal pregnancy the following results were observed: (i) serum ionic calcium levels showed no differences; (ii) urinary calcium excretion was increased as a result of increased calcium clearance. A striking feature was the fact that the fractional calcium clearance was not increased, in contrast to the increase in relative calcium clearance. The observed results can be explained by an increased GFR and a possible dissociation between the sodium and calcium handling in the cortical thick ascending Limb of Henle's Loop.