Letters to the Editor
Biochemical tests in pregnancy
- Adam Morton, Huy A. Tran
- Aust Prescr 2005;28:136-9
- 1 December 2005
- DOI: 10.18773/austprescr.2005.103
Editor, – In addition to the tests mentioned in the article 'Abnormal laboratory results: Biochemical tests in pregnancy' (Aust Prescr 2005;28:98-101), there are several other tests where the changes in the normal ranges during pregnancy are of clinical importance.
Senior staff specialist, Endocrinology and Obstetric Medicine
Mater Adult Hospital
Dr H.A. Tran, author of the article, comments:
Dr Morton's comments on other laboratory parameters that change during pregnancy are very much appreciated. The article aimed to highlight biochemical changes in common tests without being overly exhaustive. Generally speaking, pregnancy is a volume retentive, prothrombotic and nutritionally challenged state which results in all the corresponding changes described.
The hypervolaemic state is the result of an activated renin-angiotensin system with markedly elevated aldosterone concentrations and plasma renin activity. The normal physiological control of this system however remains intact, distinguishing it from primary hyperaldosteronism during pregnancy.11
The prothrombotic state is highlighted by the elevated d-dimer concentrations and reduced free protein S concentrations. The latter is the result of elevated protein binding capacity which is typical of pregnancy. Similarly, elevated transcobalamin and haptocorrin concentrations contribute to the reduction in cobalamin concentrations12although preferential fetal transfer during pregnancy also adds to the problem, particularly in vegans. It is probably more cost-effective to replenish B12storage empirically for the duration rather than relying on homocysteine concentrations to diagnose B12deficiency. Erythrocyte sedimentation rate, by way of physiological anaemia during pregnancy, is expected to be elevated but usually not to 100 mm/hour. The mean peak ranges from 50-70 mm/hour depending on the gestational age.13Thus, where it exceeds 100 mm/hour it is important that active inflammation or infection is excluded. Similarly, while white cell count can rise up to 15-16 x 106/mL, the majority often do not exceed the non-pregnant reference range.14
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Senior staff specialist, Endocrinology and Obstetric Medicine, Mater Adult Hospital, Brisbane
Head and Associate Professor, Department of Clinical Chemistry, Hunter Area Pathology Service, John Hunter Hospital, Newcastle University, Newcastle, New South Wales