The urine protein heat coagulation test—a useful screening test for proteinuria in pregnancy in developing countries: a method validation study

Authors

  • Vajira H.W. Dissanayake,

    Corresponding author
    1. Human Genetics Unit, Faculty of Medicine, University of Colombo, Sri Lanka
    2. Division of Clinical Chemistry, Institute of Genetics, School of Molecular Medical Sciences, University of Nottingham, UK
    3. Division of Obstetrics, School of Human Development, University of Nottingham, UK
      * Correspondence: Dr V. H. W. Dissanayake, Human Genetics Unit, Faculty of Medicine, University of Colombo, Kynsey Road, Colombo 8, Sri Lanka.
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  • Linda Morgan,

    1. Division of Clinical Chemistry, Institute of Genetics, School of Molecular Medical Sciences, University of Nottingham, UK
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  • Fiona Broughton Pipkin,

    1. Division of Obstetrics, School of Human Development, University of Nottingham, UK
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  • Veluppillai Vathanan,

    1. University Obstetrics Unit, De Soysa Hospital for Women, Colombo, Sri Lanka
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  • Samanthi Premaratne,

    1. University Obstetrics Unit, De Soysa Hospital for Women, Colombo, Sri Lanka
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  • Rohan W. Jayasekara,

    1. Human Genetics Unit, Faculty of Medicine, University of Colombo, Sri Lanka
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  • Harshalal R. Seneviratne

    1. University Obstetrics Unit, De Soysa Hospital for Women, Colombo, Sri Lanka
    2. Department of Obstetrics and Gynaecology, Faculty of Medicine, University of Colombo, Sri Lanka
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* Correspondence: Dr V. H. W. Dissanayake, Human Genetics Unit, Faculty of Medicine, University of Colombo, Kynsey Road, Colombo 8, Sri Lanka.

Abstract

In many parts of the developing world, the urine protein heat coagulation test is routinely used to screen for proteinuria in pregnancy. The aim of this study was to determine whether ≥1+ on a standardised heat coagulation test reliably detects significant proteinuria and to compare it with the dipstick test for urinary protein. Heat coagulation test, dipstick test and 24-hour urine protein excretion results of 102 women were compared. ≥1+ on heat coagulation test is as sensitive and specific as ≥2+ on the dipstick test in detecting proteinuria of ≥500 mg/day. The heat coagulation test, however, is less sensitive than ≥1+ on dipstick in detecting lesser degrees of proteinuria.

Introduction

The vast majority of the estimated 50,000 annual deaths due to hypertensive disorders in pregnancy occur in developing countries. Screening for proteinuria, which is routine in antenatal care, is important for early detection and successful management of women who develop pre-eclampsia. Significant proteinuria in pregnancy is defined as proteinuria of ≥300 mg/day. ≥1+ (0.3 g/L) on dipstick testing is used as a surrogate when a 24-hour urine protein estimation is not available. A stricter definition of ≥500 mg/day or ≥2+ (1 g/L) on the dipstick test may be more appropriate for research.1 These tests, although widely available in the West, are not available even in the best centres in many developing countries. What is available there is the urine protein heat coagulation test.2 Although widely used in routine clinical practice, its clinical utility has not been formally established.

The aim of this study was to determine whether ≥1+ on a standardised heat coagulation test reliably detects significant proteinuria and to compare it with the Roche Combur10 dipstick test for urine protein (Roche Diagnostics, UK).

Methods

The study was conducted in the De Soysa Hospital for Women and the Castle Street Hospital for Women in Colombo, Sri Lanka between August 2002 and April 2003. The Ethical Review Committee of the Faculty of Medicine, University of Colombo granted ethical approval for the study. One hundred and seven hospitalised pregnant women of more than 20 weeks of gestation whose proteinuria status was known based on a heat coagulation test result within the preceding 24 hours as a part of routine inpatient clinical care were recruited after obtaining written informed consent. At recruitment they passed a sample of urine and immediately thereafter began a 24-hour urine collection under supervision. A midwife or nurse performed a heat coagulation test and a dipstick test on separate aliquots of the initial sample. Midwives and nurses were trained on performing the heat coagulation test according to a standard protocol (Appendix A) and the dipstick test according to manufacturer's instructions. This dipstick test is based on the principal of the protein error of pH indicators. The 24-hour urine protein estimations were made in the laboratory using the pyrogallol red method (Randox Laboratories, UK) by a technician who was blinded to the results of the tests done in the ward. A third aliquot of the initial sample was sent to the laboratory for a sulphosalicylic acid test.3 The sulphosalicylic acid test is used routinely in Sri Lanka as a backup test when heat coagulation test is negative but there is strong clinical suspicion of significant proteinuria. Briefly, the sulphosalicylic acid test involved acidifying urine by adding 10% acetic acid, centrifugation of the sample for 5 minutes at 2000–3000 rpm, placing 2 mL of urine in a test tube, adding 2 mL of 5-sulphosalicylic acid and making a qualitative assessment of turbidity to report the result.

Results

Five women were excluded because their 24-hour urine collections were not completed. The dipstick test results of 31 women were not available because the midwife or nurse performing the heat coagulation test had either not performed the dipstick test or having performed it had not recorded the result. Sulphosalicylic acid test results were available for 88 women.

The results are summarised in Table 1. ≥1+ on the heat coagulation test was comparable with ≥2+ on the dipstick test in detecting proteinuria of ≥300 mg/day or ≥500 mg/day. ≥1+ on the dipstick test had the highest sensitivity for detecting proteinuria of ≥300 mg/day, but lacked specificity at ≥500 mg/day.

Table 1.  Comparison of the results of the heat coagulation test, the dipstick test and the sulphosalicylic acid test. All figures except sensitivity, specificity, positive and negative predictive values refer to number of women.
24-hour urine protein estimationHeat coagulation testDipstick testDipstick testSulphosalicylic acid test
Negative≥1+TotalNegative≥1+TotalNegative/1+≥2+TotalNegative≥1+Total
<300 mg/day40141242262512631637
≥300 mg/day30316193645232245153651
Total7032102333871482371464288
Sensitivity  0.51  0.80  0.49  0.71
Specificity  0.98  0.92  0.96  0.84
Positive predictive value  0.97  0.95  0.96  0.86
Negative predictive value  0.57  0.73  0.52  0.67
 
<500 mg/day5966528124037340431659
≥500 mg/day1126375263111203132629
Total7032102333871482371464288
Sensitivity  0.70  0.84  0.65  0.90
Specificity  0.91  0.70  0.93  0.73
Positive predictive value  0.81  0.68  0.87  0.62
Negative predictive value  0.84  0.85  0.77  0.93

Discussion

≥1+ on the heat coagulation test is as good as ≥2+ on the dipstick test in detecting proteinuria of ≥500 mg/day. The heat coagulation test, however, is less sensitive than ≥1+ on the dipstick test in detecting lesser degrees of proteinuria. In the West, where dipstick testing is routine in clinical practice, its sensitivity is perceived to be much higher than evidence from this and other studies would suggest.4,5 Induced diuresis is often cited as a reason for false negative dipstick results. This may be true of the heat coagulation test as well. The practice in Sri Lanka to overcome the problem of false negative heat coagulation test results is to test another aliquot of the urine sample using a more sensitive laboratory test such as the sulphosalicylic acid test when significant proteinuria is clinically suspected. In this study, of the false negatives on the heat coagulation test, 70% with proteinuria of ≥500 mg/day and 50% with ≥300 mg/day were picked up by the sulphosalicylic acid test. The sensitivity of the combined heat coagulation test and sulphosalicylic acid test based on the results of the 88 women for whom results of both tests were available was 0.90 for proteinuria of ≥500 mg/day and 0.73 for proteinuria of ≥300 mg/day. It is clear therefore that having a backup test for heat coagulation test such as the sulphosalicylic acid test would be useful in clinical settings where access to 24-hour urine protein estimations is not readily available.

The prevalence of significant proteinuria in this hospitalised series of women was high. It was 0.59 for significant proteinuria of ≥300 mg/day and 0.37 for significant proteinuria of ≥500 mg/day. The positive and negative predictive values may be distorted because of this high prevalence. These values were tested therefore across a prevalence range from 0.05 to 0.60. These results showed that the results of the heat coagulation test and the dipstick test are comparable across this range (data not shown).

Cost is an important consideration in selecting screening tests when finances are scarce. In Sri Lanka, a 24-hour urine protein estimation, a dipstick test and a heat coagulation test would cost Rs. 250.00 (£1.61), Rs. 16.40 (£0.11) and Rs 0.45 (£0.003), respectively (Rs 155 =£1).

In conclusion, the heat coagulation test is efficient and reliable in the hands of trained midwives and nurses who perform it routinely in detecting proteinuria ≥500 mg/day, and is an effective screening test suitable for use in developing countries where funding is scarce and dipsticks are not routinely available.

Acknowledgements

The authors would like to thank the patients for having consented to take part in the study and the staff of the De Soysa Hospital for Women, the Castle Street Hospitals for Women and the Asiri Hospital Laboratory in Colombo, Sri Lanka for their cooperation. This study was funded by the Sri Lanka Medical Association—Glaxo Welcome Research Award 2002. VHWD holds a PhD studentship funded jointly by the President's Fund Sri Lanka, University of Colombo, Sri Lanka and the University of Nottingham, UK.

Accepted 12 February 2004

Appendix

Appendix A.

Steps of the standardised heat coagulation test

  • 1Apply 5 mL of the urine sample into a test tube.
  • 2Add a few drops of dilute acetic acid to the tube to make the sample acidic.
  • 3Heat the urine column in the tube over a burner without boiling over.
  • 4Compare the tube against the diagrammatic result interpretation chart (Fig. 1) and record the result.
Figure 1.

The urine protein heat coagulation test result interpretation chart.

Interpretation of the heat coagulation test result

Negative/TraceNo or mild turbidity observed. When the urine column in the tube is placed in front of a typed sheet of paper, printed letters can be clearly read through the tube.
+1Definite turbidity observed. Printed letters can be clearly read through the tube.
+2Definite turbidity observed. Printed letters cannot be read clearly through the tube.
+3Definite turbidity observed. Nothing can be observed through the tube.
+4Protein clots are seen in the tube.

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