# Situation: The nurse at a Rural Health Unit (RHU) joins a team evaluating a point-of-care hemoglobin test for anemia in pregnant women. The laboratory hemoglobin test is the reference standard. Using the same results for 500 pregnant women: Point-of-care positive: 85 with anemia, 48 without anemia Point-of-care negative: 15 with anemia, 352 without anemia What is the positive predictive value (PPV) of the point-of-care test? Round off to one decimal place.

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> subject: Nursing Practice I — Community Health Nursing

## 문제

Situation: The nurse at a Rural Health Unit (RHU) joins a team evaluating a point-of-care hemoglobin test for anemia in pregnant women. The laboratory hemoglobin test is the reference standard.

Using the same results for 500 pregnant women:
Point-of-care positive: 85 with anemia, 48 without anemia
Point-of-care negative: 15 with anemia, 352 without anemia
What is the positive predictive value (PPV) of the point-of-care test? Round off to one decimal place.

## 보기

1. 26.6%
2. 36.1%
3. 63.9% **✔ 정답**
4. 88.0%

**정답: 3**

## 해설

PPV is the proportion of women who test positive who truly have anemia: true positives ÷ all positive tests × 100. There were 133 positive tests (85 + 48), of which 85 were true positives: 85 ÷ 133 × 100 = 63.9%. PPV is read across the 'test positive' row.

## 심화 해설

Understanding the 2 × 2 table

Before calculating the positive predictive value (PPV), the results must be arranged into a standard diagnostic accuracy table. The point-of-care test is compared against the laboratory hemoglobin test, which serves as the reference standard.

| Point-of-care result | Anemia present (lab positive) | Anemia absent (lab negative) | Total |
| --- | --- | --- | --- |
| Test positive | 85 (true positive) | 48 (false positive) | 133 |
| Test negative | 15 (false negative) | 352 (true negative) | 367 |
| Total | 100 | 400 | 500 |

What PPV actually means

Positive predictive value answers the clinical question: If a pregnant woman has a positive point-of-care hemoglobin test, what is the probability that she truly has anemia? It is calculated only among women who tested positive.

PPV = true positives ÷ all positive tests × 100 = 85 ÷ 133 × 100 = 63.9%

The denominator includes both true positives and false positives because every positive result—whether correct or incorrect—is what the clinician must act on. A false positive means a woman without anemia is told she may be anemic, which can lead to unnecessary iron supplementation or further testing.

Why PPV is not a fixed property of the test

PPV depends on the prevalence of anemia in the tested population. In this sample, anemia prevalence is 100 ÷ 500 = 20%. At this prevalence, the PPV is 63.9%. If the same point-of-care device were used in a population with higher anemia prevalence, the PPV would rise; in a lower-prevalence population, it would fall. This is a key distinction from sensitivity and specificity, which are intrinsic test characteristics.

Key point! Sensitivity and specificity describe the test itself. PPV and NPV describe how the test performs in a specific population. Do not confuse PPV with sensitivity.

Clinical relevance in rural and antenatal settings

Point-of-care hemoglobin testing is particularly valuable where laboratory access is limited. In low- and middle-income settings, anemia is a substantial contributor to poor pregnancy outcomes, and on-site testing can expand screening coverage [1]. Devices such as the HemoCue and Masimo Rad-67 have been evaluated in antenatal care settings precisely because timely hemoglobin results allow same-day clinical decisions [2][4]. However, the presence of false positives—48 women in this sample—means that a positive point-of-care result should be interpreted as a screening trigger rather than a definitive diagnosis.

Watch out! A PPV of 63.9% means roughly 36 out of every 100 positive results are false positives. In practice, confirmatory laboratory testing or repeat hemoglobin measurement may be warranted before initiating long-term treatment, especially when iron therapy carries side effects or when resources are constrained [3][4].

Calculation steps for the exam

1. Identify true positives: 85 (point-of-care positive and lab-confirmed anemia).

2. Identify all positive tests: 85 + 48 = 133.

3. Divide true positives by all positives: 85 ÷ 133 = 0.639.

4. Multiply by 100 and round to one decimal place: 63.9%.

The other options represent common errors: 26.6% is the false positive rate among all positive tests (48 ÷ 180 would be incorrect; actually 48 ÷ 133 = 36.1%, which is option 2), and 88.0% is the negative predictive value (352 ÷ 367). Option 2 (36.1%) is the complement of PPV—the proportion of positive tests that are false positives—so selecting it reflects a misunderstanding of which row to read.

PPV is always read across the test positive row: true positives divided by the entire positive row total.References (research sources)

- [1]Accuracy of on-site tests to detect anemia during prenatal care.Research articleSobhy S, Rogozinska E, Khan KS (2017) · DOI: 10.1002/ijgo.12289

- [2]Diagnostic accuracy of a non-invasive spot-check hemoglobin meter, Masimo Rad-67® pulse CO-Oximeter®, in detection of anemia in antenatal care settings in Kenya.Research articleKoech A, Mwaniki I, Mutunga J, Mukhanya M, Mwadime E, Ochieng M (2024) · DOI: 10.3389/fgwh.2024.1427261

- [3]Comparative Diagnostic Accuracy of Clinical Pallor at Different Anatomical Sites for Detecting Anemia in Pregnant Women Using HemoCue® as the Reference Standard.Research articleJegadeesan D, Rajendran V, Rajamanickam S. (2026) · DOI: 10.7759/cureus.114293

- [4]Diagnostic and analytic performance of four point-of-care hemoglobin testing devices used in routine HIV and maternity care in Uganda.Research articleSsuuna C, Nakawooya H, Muwanika R, Kankaka EN, Galiwango RM, Nyegenye W (2025) · DOI: 10.1186/s12913-025-13354-9

## 임상 시나리오

PPV in Anemia ScreeningInterpreting a Positive Point-of-Care Result
When a point-of-care hemoglobin test is positive in a pregnant woman, the positive predictive value (PPV) tells you the chance she truly has anemia. In this cohort, PPV is 63.9%, meaning about 2 out of 3 positive results are true anemia.

PPV is calculated only from the test positive row: true positives (85) divided by all positive tests (85 + 48 = 133). False positives are included because every positive result must be acted upon clinically.

CautionPPV is not fixed; it depends on anemia prevalence in the screened population. The same device will have higher PPV in high-prevalence settings and lower PPV where anemia is rare.

## 핵심 개념

- **Positive Predictive Value** — Probability that a person with a positive test truly has the disease; calculated as true positives divided by all positive tests.
- **True Positive** — A test result that correctly identifies a person with the disease.
- **False Positive** — A test result that incorrectly identifies a person as having the disease when they do not.
- **Prevalence** — The proportion of a population that has a specific disease at a given time; affects PPV.
- **Reference Standard** — The best available method for establishing the presence or absence of a condition, used for comparison.

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