Is it a problem if the red color on the pregnancy test stick has diffused?

Nov 15, 2025 Source: Cainiu Health

Dr. Zhang Lu

Introduction

If the red dye area on the pregnancy test strip is small, but the control line (C-line) is still clearly visible and the test line (T-line) is discernible (regardless of its intensity), and the reading is taken within the 5–10 minute window specified in the instructions, the result is generally reliable. The faint staining may be due to slightly excessive sample volume or minor moisture exposure affecting the test strip, but this does not impact result interpretation. You can determine pregnancy status based on the clear appearance of the lines.

Under normal circumstances, if the red smearing on a pregnancy test stick allows clear differentiation of the control line (C-line) and test line (T-line), and the result is read within the specified time, it is usually not a concern. However, if the lines are completely blurred and indistinguishable, or if the reading is taken beyond the recommended time, the result may be unreliable. If in doubt, it is advisable to seek medical advice promptly. Detailed explanations are as follows:

If the area of red smearing on the pregnancy test stick is small, and both the control line (C-line) and test line (T-line) remain clearly visible (regardless of the intensity of the T-line color), and the test is observed within the 5–10 minute window specified in the instructions, the result is generally reliable. The smearing may result from slightly excessive sample volume or minor moisture exposure affecting the test strip, but this does not interfere with interpretation. Pregnancy status can be determined based on the clearly visible lines.

If the test stick shows complete red smearing, making both the C-line and T-line indistinguishable, or if smearing appears only after exceeding the recommended reading time (more than 30 minutes, or 20 minutes for some products), the result may be invalid. In such cases, accuracy cannot be guaranteed. This may be due to user error (e.g., too much liquid applied), expired test strips, or moisture damage causing test failure. Pregnancy status cannot be reliably determined, and retesting is required.

Prior to using a pregnancy test, always check the expiration date and ensure the packaging is intact. Strictly follow the instructions regarding sample volume and reading time. If red smearing interferes with result interpretation, replace the test with a new one and retest using first-morning urine to ensure accurate results.

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Is pinkish blood a sign of menstruation or pregnancy?

In general, pinkish blood may either be a sign of menstruation or an early sign of pregnancy. It is important to maintain external genital hygiene by washing with warm water, wearing breathable cotton underwear, and changing it frequently. Avoid strenuous exercise, spicy foods, and maintain a regular sleep schedule. If the cause is uncertain, promptly take a pregnancy test or consult a healthcare provider to determine the cause and prevent delays in appropriate management.

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Will taking emergency contraceptive pills affect the results of a pregnancy test?

In general, the impact of pregnancy after taking emergency contraceptive pills depends on the specific circumstances. If the embryo develops normally, there is usually no need for excessive concern; however, symptoms such as abdominal pain or bleeding may indicate potential adverse effects of the drug on the pregnancy. During pregnancy, it is important to maintain a regular作息 (daily routine), avoid staying up late and overexertion. Maintain a balanced diet with adequate intake of high-quality protein and fresh fruits and vegetables, and avoid smoking, alcohol, and other harmful substances.

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Why is the pregnancy test strip line remaining faint and not getting darker? What should I do?

In general, if a pregnancy test strip remains faint and does not get darker, it may be due to short gestational age, improper testing method, poor embryonic development, endocrine disorders, ectopic pregnancy, or other causes. It is recommended to seek medical attention promptly, identify the underlying cause, and follow a doctor's guidance for appropriate management. Daily relaxation and avoiding excessive anxiety are also important.

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How soon can a pregnancy test strip show a positive result with one dark line and one faint line?

Pregnancy test strips determine whether a person is pregnant by detecting the concentration of HCG in urine. After intercourse, it takes about 6–7 days for the fertilized egg to implant, after which HCG levels gradually rise and typically reach detectable levels by the test strip around 14 days. In a result showing one dark and one faint line, the darker line is the control line, while the fainter line is the test line, indicating low HCG concentration, which may suggest an early stage of pregnancy or slower embryonic development.