Ferning and umbilical blood samples

Volume 162 Number 5

platelet count in the specimen. The amount of contamination required to lower all three parameters below the normal limits has not been described in the literature. In this study complete blood counts were not performed on the contaminated specimens. The ferning test may also be useful for the rapid confirmation of suspected ruptured membranes in the presence of vaginal bleeding, as in cases of placenta previa. The method would be much faster and more economical than assaying the vaginal specimen for a-fetoprotein or prolactin. In summary, the ferning test is a simple, inexpensive, rapid, and accurate means of detecting amniotic fluid contamination of blood specimens, and holds promise for quality control application to the technique of percutaneous umbilical blood sampling.

REFERENCES 1. Ludomirski A, Weiner S. Percutaneous fetal umbilical blood sampling. Clin Obstet Gynecol 1988;31:19-26. 2. Brookes C, Shand K, Jones WR. A reevaluation of the ferning test to detect ruptured membranes. Aust N Z J Obstet Gynaecol 1986;26:260-4. 3. Borten M, Friedman EA. Amniotic fluid ferning in early gestation. AM J OSSTET GY»;ECOL 1986; 154:628-30. 4. Daffos F, Capella-Pavlovsky M, Forestier F. Fetal blood sampling during pregnancy with use of a needle guided by ultrasound: a study of 606 consecutive cases. AM J OSSTET GY;\IECOL 1985; 153:655-60. 5. Kovacs D. Crystallization test for the diagnosis of ruptured membranes. AM J Os STET GY1';ECOL 1962;83: 1257-60.

Is pH test paper as accurate as the electronic measurement of the pH of vaginal secretions? Jessica L. Thomason, MD, Sheldon M. Gelbart, PhD, Lisa M. Monagle, RN, Janine A. James, MD, and Fredrick F. Broekhuizen, MD

Milwaukee, Wisconsin A comparison was made of two brands of pH test paper and electronic instrumentation for measuring the pH of vaginal secretions. When the pH of vaginal secretions was >4.5 (abnormal), there was no significant difference between the methods, showing that pH test paper is reliable for pH determination of vaginal secretions. (AM J OSSTET GVNECOL 1990;162:1213-4.)

Key words: pH, vaginal secretions Increased pH of vaginal secretions is an important sign that aids in the diagnosis of several vaginal disorders (e.g., bacterial vaginosis and trichomoniasis).1 Vaginal pH is generally determined by the use of test papers as recommended by Gardner and Dukes' in 1955. Despite vast improvements in technology of both pH instrumentation and test papers, a comparison of these methods for measuring vaginal pH has not been reported since 1955.' The purpose of this study was to compare two types of pH test papers to state-of-the-art pH instrumentation to determine how reliable pH test From the Department of Obstetrics and Gynecology, University of Wisconsin Medical School. Receivedfor publication July 20,1989; accepted December 4.1989. Reprint requests,' J. L. Thomason, M D, Division of Gynecology, Sinai Samaritan Medical Center, P.O. Box342, Milwaukee, W1532010342. 611118610

paper measurements were when used in the clinical situation. Vaginal secretions were collected from 64 randomly selected, non menstruating, premenopausal women, who had given consent. Samples were obtained from the lateral vaginal fornix on three dry cotton-tipped swabs. Care was taken to avoid any cervical mucus. Swabs were unlabeled when presented to the technician. This was done to obtain randomization of sampling because the technician did not know the order in which the swabs were obtained. Vaginal secretions were tested immediately for pH by the following methods: one swab was touched to the surface of Nitrazine pH test paper (E. R. Squibb & Sons Inc., Princeton, N.J.). The pH was read according to the color indicated per manufacturer's instructions. A second swab was probed with an MI415 Microcombination pH probe (Microelectrodes, Inc., Londonderry, N.H.), and the pH was 1213

1214 Thomason et al.

May 1990 Am J Obstet Gynecol

Table I. Comparison of vaginal pH determinations by pH test papers and pH instrumentation in 61 evaluable patients ColorpHast vs meter

Mean Variance SD SE t Value P Value

4.55 0.35 0.59 0.08

1.040 0.303

4.51 0.48 0.69 0.09

read from an Orion model 301 pH meter (Orion Research Inc., Cambridge, Mass.). The electrode can measure quantitites as small as 0.5 ,""I, and the meter is accurate to ± 0.04 pH units. The meter was calibrated with pH reference buffers at pH 4.01 ± 0.01 and pH 7.00 ± 0.01 (American Hospital Supply Corp., McGaw Park, 111.). A third swab was touched to ColorpHast pH test paper (E. Merck, Darmstadt, West Germany). The pH was read according to the color indicated per manufacturer's instructions. Statistical evaluation was performed with Student's paired t test. Three (5%) patients were found to have insufficient amounts of discharge to allow any measurement. The data from 61 evaluable patients are presented in Table I. There was no statistically significant difference between ColorpHast pH test paper and the pH instrumentation, but there was a statistically significant difference between Nitrazine pH test paper and both ColorpHast paper and instrumentation. The reason for this difference was not the accuracy of Nitrazine paper but rather the lower limit of pH that can be determined. Nitrazine shows all pH values :54.5 as 4.5. This limits the data obtained by this method because more than one third of our patients (n = 23) had vaginal pH of 3.8 to 4.0, as determined by the instrumentation method. When examining data only from women whose vaginal pH was >4.5 as determined by instrumentation, there was no statistical difference between the Nitrazine and ColorpHast papers. We conclude that pH test paper is as reliable as pH instrumentation for obtaining pH measurements of vaginal secretions for diagnostic purposes because val-

Nitrazine vs meter

4.74 0.21 0.41 0.06

2.101

Is pH test paper as accurate as the electronic measurement of the pH of vaginal secretions?

A comparison was made of two brands of pH test paper and electronic instrumentation for measuring the pH of vaginal secretions. When the pH of vaginal...
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