Platelet-to-Lymphocyte Ratio (PLR)

What the PLR is and when it is used

The PLR is the ratio between the platelet count and the absolute lymphocyte count, both from the same complete blood count. It reflects, in a single number, two frequent changes in inflammatory states: an increase in platelets and a fall in lymphocytes.

Gasparyan and colleagues, in a review article published in the Annals of Laboratory Medicine in 2019, describe the PLR as a marker of changes in platelet and lymphocyte counts in acute inflammatory and prothrombotic states. The ratio has been widely studied in neoplastic diseases and in inflammatory rheumatic diseases.

In oncology, the meta-analysis by Templeton and colleagues (Cancer Epidemiology, Biomarkers & Prevention, 2014) pooled 20 studies with 12,754 patients and associated a high PLR with shorter overall survival in several solid tumors. The PLR is a close relative of the neutrophil-to-lymphocyte ratio (NLR), which uses the same denominator, and both come from the same blood count as the red cell indices.

How to use the calculator: inputs and result

The calculator asks for two absolute counts from the same blood count:

• Platelets (absolute count). Example: 250000 or 250. The field does not accept negative values.
• Lymphocytes (absolute count), greater than zero. Example: 1500 or 1.5.

The examples show two report formats: in cells/µL (250000 and 1500) or in ×10³/µL, equivalent to ×10⁹/L (250 and 1.5). Both counts must be in the same format.

Zero lymphocytes, negative values or counts that appear to be in different units (for example, 250000 and 1.5) produce an error message. The tool shows the PLR, unitless, with one decimal place.

There is no classification into ranges, because no published normal range exists for the PLR. A text explains that cutoffs such as 150 and 300 come from prognostic studies in specific populations, and a note reminds you that the marker is nonspecific. With the example values in the fields, the PLR is 166.7.

PLR formula and worked example

The PLR is the platelet count divided by the lymphocyte count:

PLR = Platelets ÷ Lymphocytes

Both counts must be in the same unit, and the result is unitless.

Didactic example (not an interpretation of a patient): 300,000 platelets/µL and 1,500 lymphocytes/µL.

1. PLR: 300,000 ÷ 1,500 = 200.0.
2. Comparison with the literature: the value lies between the cutoffs of 150 and 300 used in the studies by Templeton and colleagues, which apply to patients with solid tumors.

The same blood count reported in ×10³/µL (300 and 1.5) gives the same result: 300 ÷ 1.5 = 200.0.

Unlike the NLR, the PLR cannot be calculated with percentages from the white cell differential, because platelets are not part of the leukocyte differential count. You need to use the absolute lymphocyte count, obtained from the report or calculated as total leukocytes × lymphocyte percentage ÷ 100. For example, 6,000 leukocytes/µL with 25% lymphocytes correspond to 1,500 lymphocytes/µL.

How to understand the PLR: cutoffs used in studies

The PLR has no single reference value, and the cutoffs depend on the study and the population. In the meta-analysis by Templeton and colleagues, the cutoffs that defined risk groups ranged from 150 to 300. Twelve studies used a single cutoff, and eight divided patients into three groups: below 150, from 150 to 300 and above 300.

That is why the calculator shows only the value, without normal or elevated labels. In the meta-analysis, the groups were used to estimate prognosis in patients with cancer, not to define normality in healthy people.

Templeton's results also show that the association varied with the type of cutoff: it was significant in studies with a single cutoff and not significant in studies with three groups. According to Gasparyan and colleagues, the value of the PLR increases when it is read together with other indices, especially the NLR. Individual interpretation is the responsibility of the professional.

Common errors, units and checklist

The most common error with the PLR is mixing units between platelets and lymphocytes. Examples:

• Platelets in ×10³/µL and lymphocytes in cells/µL: 250 ÷ 1,500 would give 0.2 instead of 166.7; the calculator detects this pattern and shows an error.
• Platelets in cells/µL and lymphocytes in ×10³/µL: 250,000 ÷ 1.5 would give 166,666.7; this also produces an error.
• Lymphocyte percentage instead of the absolute count: 250,000 ÷ 25 gives 10,000, which is meaningless.
• Different blood counts: both counts must come from the same sample.
• Platelet clumping in the sample: clumps can lower the automated platelet count, and the result should be confirmed by the laboratory.

Gasparyan and colleagues point to preanalytical errors, lack of standardization of laboratory measurements and inadequate selection of participants as the main limitations of PLR studies.

Checklist before using the result:

• Are platelets and lymphocytes in the same unit?
• Are the lymphocytes an absolute count, not a percentage?
• Are both counts from the same blood count?
• Does the cutoff used for comparison come from a study with a similar population?

When the PLR may be inappropriate

The PLR depends on two counts that change for many reasons, and this limits the reading of an isolated value. Any condition that alters only the platelets or only the lymphocytes changes the ratio, unrelated to inflammation.

Situations that call for caution:

• diseases that reduce or increase platelets through their own mechanisms, such as hematological diseases;
• conditions and treatments that reduce lymphocytes;
• populations and conditions different from those studied: Templeton's cutoffs come from patients with solid tumors;
• children, for whom no cutoffs have been established.

Gasparyan and colleagues report that longitudinal studies in rheumatic diseases observed a fall in the PLR with anti-inflammatory treatment, which suggests usefulness in monitoring. Even so, the PLR is a nonspecific marker and complements, without replacing, clinical assessment and other tests.

PLR, NLR and other platelet indices

The PLR is almost always analyzed alongside the NLR, because both share lymphocytes in the denominator. The table summarizes the differences:

According to Gasparyan and colleagues, PLR and NLR have high predictive value in rheumatic diseases with predominantly neutrophilic inflammation, and the NLR adds information on disease activity and infectious complications. Calculate the NLR with the same blood count in the NLR calculator. The red cell series can be checked with the red cell indices, and the marrow response to anemia with the reticulocyte production index.

Frequently asked questions about the platelet-to-lymphocyte ratio (PLR)

References

1. Templeton AJ, Ace O, McNamara MG, Al-Mubarak M, Vera-Badillo FE, Hermanns T, et al. Prognostic role of platelet to lymphocyte ratio in solid tumors: a systematic review and meta-analysis. Cancer Epidemiol Biomarkers Prev. 2014;23(7):1204-12. doi:10.1158/1055-9965.EPI-14-0146. View
2. Gasparyan AY, Ayvazyan L, Mukanova U, Yessirkepov M, Kitas GD. The platelet-to-lymphocyte ratio as an inflammatory marker in rheumatic diseases. Ann Lab Med. 2019;39(4):345-57. doi:10.3343/alm.2019.39.4.345. View
3. Zahorec R. Neutrophil-to-lymphocyte ratio, past, present and future perspectives. Bratisl Lek Listy. 2021;122(7):474-88. doi:10.4149/BLL_2021_078. View