Within 2 hours after the onset of acute illness (and after 24– 36 hours of fasting), T3 levels decrease and rT3 levels rise. The magnitude of these changes is related to the severity of the disease. T3 levels decrease progressively with increasing severity of disease without reaching a nadir, whereas rT3 increases in relation to severity of disease, but reaches a plateau. rT3 is not invariably elevated in all causes of NTI.

In mild illness, total and free T4 (fT4) levels may rise initially after the onset of disease but in severely ill patients, T4 levels drop as well. Both low T4 and T3, as well as high rT3 are associated with a worse prognosis. Thyroid- stimulating hormone (TSH) may rise briefly for ~2 hours after the onset of disease, but despite the drop in serum T3 (and eventually also in T4), TSH usually remains within the (low) normal range.

Duration of illness is another important determinant of the thyrotropic profile in NTI. Patients requiring intensive care enter a more chronic phase of NTI, and the low levels of thyroid hormone in prolonged illness have a more neuroendocrine origin. Pulsatility and circadian variation in TSH secretion is diminished in prolonged illness and hypothalamic thyrotropin- releasing hormone (TRH) mRNA expression in patients who died from chronic severe illness is low compared to patients who died from an acute trauma. Low TSH secretion and TRH expression correlate with low serum T3. Reverse T3 levels remain elevated or may return back to normal with the decrease in serum T4. Type of illness and feeding status are also important.

Both low T4, low T3, and high rT3 levels are associated with a worse prognosis. A study in 451 patients who received intensive care for at least 5 days, showed that TSH, T4, T3, and the T3/ rT3 ratio increased in patients who survived, but not in non- survivors. Patients who died after critical illness had lower tissue T3 compared to patients who had died acutely, but the severity varies from one organ to another. Low serum T4 and T3 correlated well with local concentrations in liver and skeletal muscle.

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Microorganism Entry, Invasion, and Dissemination: The Host’s Perspective

Microorganism Colonization of Host Surfaces

The Encounter Between Host and Microorganism

Systemic Approach to Anemia

Comparison of Etiologies of Anemia in Adults and Children

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Nosology of Hemoglobinopathies

Infections of the Urinary Tract: Types of Infection and Their Clinical Manifestations

Toxic Goitre

Infections of the Urinary Tract : Pathogenesis

Infections of the Urinary Tract : Etiologic Agents