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EDITORIALS: Lucy C Chappell and Andrew H Shennan Assessment of proteinuria in pregnancy BMJ 2008; 336: 968-969 [Full text]

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Pregnancy, hypertension,proteinuria and blood viscosity.

Les O. Simpson   (16 April 2008)

Pregnancy, hypertension,proteinuria and blood viscosity. 16 April 2008
Les O. Simpson, retired medical research worker Dunedin, New Zealand 9077 Send response to journal: Re: Pregnancy, hypertension,proteinuria and blood viscosity.	The contents of both the article and the related editorial concerning the significance of proteinuria in pregnancy raise the question the importance of early studies. Do studies reporting factual information, but published in the 1980s become irrelevant because of their age ? Or do early studies simply fall out of fashion because of the nature of the technology involved ? Is quantitative assessment of proteinuria more informative than qualitative information ? It is difficult to understand how it is possible to discuss proteinuria associated with hypertension during pregnancy without reference to the published information concerning the role of blood viscosity. A review on blood viscosity was published in 1911, and the relationship between blood viscosity and blood pressure was reported first in 1930. There have been many other confirmatory reports. Despite this information, the problem of high blood pressure is considered to be a vascular problem and treated accordingly. The presence of viscous blood in the glomerular afferent arteriole will influence both the quality and quantity of the glomerular filtrate. But because of the haemoconcentrating effects of glomerular filtration, blood in the efferent arteriole will be hyperviscous and will have an adverse effect on blood flow in the peritubular plexus. As a result tubular function will be impaired. Therefore it can be expected that when blood viscosity is increased, both the amount and the size of the proteins in the urine will be increased. Polycythemia provides a good example of the effects of blood viscosity on proteinuria. A male with a haematocrit of 60% produced a high molecular weight proteinuria, but when his haematocrit was lowered to 45% by venesection, there was very low level of microalbuminuria. A Hungarian study published in 1999 found that calcium dobesilate reduced blood viscosity, proteinuria and blood pressure in patients with pregnancy-induced hypertension. Although the editorial noted, "Pre-eclampsia is a multi-organ syndrome," there was no recognition that increased blood viscosity could be the linking factor which could affect all tissues. So it is relevant that in 1982, Hobbs et al had published an article, "Whole blood viscosity in preeclampsia." They concluded, " It is suggested that measurement of whole blood viscosity may be clinically useful in the management of patients with preeclampsia." A PubMed search for "Pre-eclampsia and blood viscosity," produced 58 titles since 1974. Forty of those articles were published by 1990 and included papers from Australia, Bulgaria, China, France, Germany, Russia and the UK. Such reports dealt with observations which showed increased blood viscosity in the third trimester and the benefits which followed a reduction in blood viscosity. It could be of some significance that only six related papers have been published since 2000. Therefore, if the primary problem is increased blood viscosity, which will increase blood pressure and impair renal function, is the spot test really relevant ? Would it not seem more appropriate to follow the 1982 suggestion of Hobbs et al, and measure whole blood viscosity, so that the primary problem could be treated ? Competing interests: None declared